PHISICAL, TECHNOLOGICAL AND BIOLOGYCAL BASE OF RADIOTHERAPY.
RADIATION THERAPY OF MALIGNANT TUMORS.
The Austrian physician Hugo Gliazer wrote: “Medicine, serving the people, consists of science and art and over them stretches a wonderful covering of heroism”. It’s hard to think up another definition for radiation therapy. This clinical discipline has traversed comparatively short but glorious historical path – from the first timid attempts of treatment the dermal diseases by X-rays (1896 ) to the widely-recognized method of treatment the patients with malignant tumors and some non-malignant diseases.
Nowadays the history of radiation therapy embodies “the drama of ideas”. On the early stage the usage of X-rays was based on the empiric data. The method was applied for treatment of dermal diseases and mycotic lesions (with the purpose of removing the hair – epilation). In 1902-
The third period of radiation therapy is connected with the name of French radiologist Clode Rego. Contrary to the conception of the second period he and his collaborators aimed to avoid necrosis and burn as well as to obtain the selective tumor destruction with the least damage of surrounding structures. In classic experiments (1919) the repeated irradiation courses in comparatively small doses were shown to be much more effective than momentaneous influences. In 1922 C.Rego presented to the International Congress of Otorhinolaryngologists 6 patients with larynx cancer who showed the excellent results of radiation therapy. Three of them felt themselves well even 15 years after the treatment. From that time it became clear that radiation therapy is an independent speciality and neither surgeons and gynecologists nor oncologists must be involved into it because, besides the technical knowledge, it was required the special attention to the problems of radiobiology. It should be mentioned that French and Russian radiologists of that time put the principle of individual approach to the patient on the first place. They were more interested in the patient’s state than in volume of irradiation dose. “Here is our scalpel and here are X-rays.
Soon, we’ll probably get one more biological or chemical factor. This is a destiny of all the coming and passing traditions. Let us separate ourselves from them, and before leaving we’ll continue to serve our God, which is Care and Love” (C.Rego).
The third period was characterized by treatment in the conditions of careful clinical examination but without any premediated plan. This period was changed by the fourth one. The group of English physicians and radiologists (so called
Basing on the conceptions of previous stages, the modern fifth period of radiation therapy began. It was marked by cooperation of specialists, combination of physico-dosimetric, technical, clinical and radiobiological approaches to the treatment of each patient with tumoral or non-tumoral disease.
I. PRINCIPLES OF RADIATION ONCOLOGY (STRATEGY OF RADIATION THERAPY OF MALIGNANT TUMORS)
The early diagnostics of tumoral process is the main strategic basis of successful surgical, radiation and medicamentous treatment. Modern oncology is a multi-disciplinary science. The treating strategy is defined by interaction of surgeon (oncologist), radiotherapeutist and chemotherapeutist. The proper choice of treatment method is, in fact, the critical moment for the patient. It is said that the first chance of cure the malignant tumor is often the last one and it can’t be missed. The mistaken choice can be fatal for the patient.
Three main variants of the patient’s treatment: surgical, radiation and medicamentous (chemotherapy) are used in oncological clinic. Treatment can be only surgical, radiation or medicamentous. It can include combination of surgical intervention and irradiation or combination of chemotherapy course and irradiation (combined treatment).
The purpose of combination of radiation and surgical methods is the destruction of radiosensitive cells in the tumor and in the zone of its subclinical distribution by means of irradiation and operative removing the central tumor nucleus, where the radioresistant hypoxic cells are concentrated. At last, the complex, consisting of surgical operation, irradiation and chemotherapy courses (complex treatment) is often used. Radiation therapy plays an important role in this complex. So, according to L.P.Simbirtseva’s data (1987) radiotherapy is applied at the tumors of cervix uteri in 98%, oral and pharyngeal cavity – in 93%, larynx – in 82%, skin – in 78%, mammary gland – in 52,3%. In general, radical or palliative radiation treatment is used in 50-60% of all the oncological patients.
In the basis of medical application of ionizing irradiation is their biological action, i.e. the ability to cause changes in the cells, tissues, organs and in the whole organism. This action is always injuring by its nature and it is marked in functional and anatomical changes in irradiated organs and in the whole organism.
The level of injuries, occurring because of irradiation, is different. Small injuries cause the intensification of regenerative abilities of the tissues and in some cases they result iormalization of disturbed functions, while the high level of injury stipulates such changes which are followed by the dystrophic processes and the destruction of cells and tissues.
Biological action is rendered by that part of radiation energy, which has been passed to the tissues. It is called the absorbed radiation dose. In the case of oncologic disease tumor serves as “a target”. The strategy of radiation treatment is based on the knowledge of physics of ionizing irradiation, especially, their interaction with biological substrate and on the data of clinical radiobiology.
Ionizing radiation is the powerful medical factor and it should be accurately dosed and brought to the tumor in strictly measured portions and in definite time intervals. It’s carried out with the help of different methods and technical devices.
Existing methods of patients’ irradiation are divided into two groups: 1) distance; 2) contact. At the distance methods the source of radiation is located at the distance from the patient. At the contact methods the source of radiation adjoins to the pathological nidus. It is carried out by means of location of radioactive preparations on the surface of irradiated zone (application method), their administration into the organ’s cavity (intracavitary irradiation) or directly into the tumor tissue (intratissue method).
Distance gamma therapy.
Contact radiotherapy.
Intracavitary radiotherapy (Cancer of the cervix).
Intratissue radiotherapy
The variety of contact method is the application of radioactive preparations in liquid aggregate condition (true or colloid solution) for peroral or intravenous administration. It should be also marked that for the treatment of some diseases combine simultaneous or consequent distance and contact irradiation. Such methods is called a combined radiotherapeutics. The indications for radiotherapeutics are defined both by the clinicist and radiotherapeutist basing on the detailed evaluation of the condition of the patient’s organs and their systems as well as the characteristic of the revealed tumor lesion. Here exists the main principle: “ to treat not the tumor but the patient with the tumor disease”.
Hence it’s the necessity of complete individual diagnosis. “It’s impossible to treat the irrecognizable disease”. Irradiation is the powerful factor of influence both on the tumor and on the human organism. That’s why, with the help of clinical, radiation, instrumental and laboratory methods determine the condition of the patient’s organs and their systems, localization and the nature of the tumor’s growth, the stage of its development. When it is possible, the stage is ascertained by TNM system, where T – tumor parameters, N – presence or absence of involving the lymphatic nodules, M – presence or absence of the removed metastases. In the most cases it is demanded the morphological confirmation of clinical diagnosis by means of biopsy, cytological study of punctuates and washings off.
In all the cases of radiation therapy application the treating complex is directed to the damage of the tumor, preserving the surrounding healthy tissues and strengthening the organism’s defense system.
The treatment of malignant tumors can be radical, palliative and symptomatic. The radical treatment provides the complete destruction of tumor elements both in the primary nidus and in the zones of possible metastases. Such a treatment can be carried out at accurately delimited tumors in the absence of metastases or with solitary ones in the regional lymphatic nodes and at the absence of the removed metastases. The aim of palliative treatment is to prolong the patient’s life, to dilay the tumor’s growth and spreading.
Symptomatic therapy is the variety of palliative treatment. It is carried out to remove the most severe signs of disease, for example, pain in the bones due to cancer metastases or circulation disturbance and tissue edema at the vena cava superior squeezing by the tumor.
The indications and contra-indications to radical, palliative or symptomatic therapy are determined basing on the patient’s examination (individually).
The indications to the radical therapy are mainly those cases when the tumor can’t be removed by operative method. At the radiosensitive tumors it is used the course of irradiation, often combined with chemotherapy. At radio resistant neoformation’s, especially within early stage, the combination of irradiation course with surgical intervention is preferable. Radiotherapeutics is often used independently at cutaneous carcinoma, cancer of the oral cavity, tumors of gullet and larynx, tumors of hypophysis, esophagus, mammary gland, small-cellular forms of pulmonary cancer, carcinoma of uterine cervix and body, urinary bladder, rectum and some other localizations. Radiotherapeutics of malignant lymphomas, seminomas, Yuing’s tumor is of great importance. It is also indicated at tumor relapses after surgical or combined treatment as well as at the local metastases into lymphatic nodes, bones and lungs.
Radiotherapeutics shouldn’t be used at the very severe patient’s state, severe exhaustion, anemia and leucopoenia, acute septic conditions, decompensated injuries of cardio-vascular system, liver, kidneys. Relative contra-indication is active pulmonary tuberculosis. Tumor spreading onto neighboring hollow organs and its germination into large vessels belongs to the local contra-indications. The treatment always complicates accompanying inflammatory process, which should be treated medicamentously.
After decision concerning the necessity of radiotherapeutics application it should be made the plan of patient’s treatment. It consists of three main items: 1) clinical and radiobiological substantiation of influence; 2) dosimetric planning of irradiation; 3) technological providing of the course of radiotherapeutics.
2. CLINICAL AND BIOLOGICAL BASES OF RADIATION TREATMENT OF TUMORS
Radiation treatment of patient is based on the principles of experimental and clinical radiobiology. They allow planning the necessary total dose of irradiation and optimum regimen of radiation influence. The irradiation effect on the tumor tissue is quite appropriate to be studied here, because tumor is the object of radiation energy.
2. 1. Effect of Ionizing Irradiation on the Tumor.
Tumor is a complex cellular system with definite internal structure. Both cellular population and non-cellular components of connective tissue are combined in it in different ratios. This system reacts on irradiation in accordance with general radiobiological regularities.
Both photons and corpuscular irradiation cause various injuries in DNA molecules of tumor cells type mono- and difilamentous ruptures, changes of nitrous bases, saturations DNA- protein. Swelling and vacuolation of the nucleus, mitochondria, cisterns and ductules of endoplasmatic reticulum and Golgi complex, exfoliation and lacerations of membranes are determined at electronic microscopy. The cells perish after a number of divisions because of genic mutations and chromosomal aberrations, caused by damage of nucleoproteins. A lot of giant cells also appear in the tumor. These are the cells which have lost the ability for fissiparity but they still continue to grow. Cell nuclei take the unusual shape. They accumulate chromatin in fettle of separate blocks. Vacuoles appear in cytoplasm. The tumor is lacerated into separate fragments by expanding granular tissue. This tissue contains surplus quantity of capillaries, epithelioid and lymphatic cells, histiocytes, fibroplasts. Significant changes occur in the vessels, nourishing the tumor. Small vessels obliterate and disturb the tissue trophicity. Endophlebitis and endoarteritis in large vessels develop, that also leads to disorders of tumor supplying. At the sufficient radiation dose all tumor cells perish and granular tissue gradually transforms into cicatricial one. The large number of factors determines radio sensitivity of the cell, i.e. its reaction on irradiation. It depends on the patient’s age and condition, condition of surrounding tissues, histological type of neo formation, correlation of content of cellular and stromal elements, velocity of cellular repopulation, availability of necrotic areas, amount of cells with low content of oxygen. Among all the factors obviously predominate two: the number of hypoxic cells and the number of non-proliferating resting clonogenic elements. The tumors of any and even the same histological structure always contain both undifferentiated, and differentiated cells. Vascularisation and oxygenation of these cells is not similar: there are the cells, normally saturated by oxygen, with lowered saturation (hypoxic) and sharply lowered saturation (anoxic). The quantity of different cells depends on blood supply, stroma development, condition of vascular bed in tumor etc. The appearance of hypoxic cells is promoted by the lowered perfusion pressure and local expansion of the vessels, as well as by the presence of multiple аrteriovenous anastomoses through which the arterial blood is thrown into venous bed of blood flow not having saturated tumor tissue by oxygen. On early stages of tumor development the percentage of hypoxic cells is small, but it significantly increases with the tumor’s growing. At the tumor irradiation the cells with high content of oxygen perish, while the hypoxic cells survive and serve the source of the further growing. For destruction of these cells is required a very high dose of radiation (approximately three fold higher, than for oxygenated cells), which exceeds the endurance of surrounding normal tissues. Healthy tissues of human organism and tumoral tissue don’t differ a lot by their radio sensitivity. The reasons of tumoral radio resistance are, as it was above mentioned, a great number of hypoxic cells and ability of tumor to fast repopulation. The success of radio therapeutics depends on the largest concentration of radiation dose in tumors and directed change of tumor radio sensitivity and surrounding it normal tissues by means of different facilities and methods. Consequently, the central problem of radio therapeutics is artificial management of radiation reactions of normal and tumoral cells with the purpose of maximum tumor damage and preserving the normal tissue elements. The facilities, which intensify the tumor defeat or weaken the radiation reactions of healthy cells, are called radio modifying agents.
2.2. Management the radiation reactions of the tumors and normal tissues.
The oldest way of management the radio sensitivity of tumoral and normal tissues is the change of irradiation conditions – variation of total and single doses, rhythm and time of irradiation, i. е. mode of irradiation conditions.
2.2.1. The choice of irradiation mode. The first problem is leading to the tumor the optimum total dose. The optimum is considered to be the level, under which is reached the top possible percentage of curing under the acceptable percentage of radiation damages of normal tissues. Actually, optimum is the total dose, under which more than 90% patients with the tumors of given localization and histological structure are cured and the damages of normal tissues occur io more then 5% patients. The importance of localization is underlined because of great variety of complications. At the treatment of tumors in vertebral region even 5% radiation myelitis and at larynx irradiation – even 5 % necrosis of its cartilages are inadmissible. Basing on experimental and clinical studies the approximate efficient absorbed doses has been determined. The microscopic units of tumoral cells in the zone of sub clinical tumors spreading can be liquidated at irradiation dose 45-50 Gy of separate fractions during 5 weeks. Approximately the same irradiation volume and rhythm allow to destroy such radiosensitive tumors as typical malignant lymphomas. For deleting the cells of planocellular cancer and adenocarcinoma is required the dose 65-70 Gy during 7-8 weeks and radio resistant tumors – sarcomas of bones and soft tissues – over 70 Gy approximately during the same period. In the case of combined treatment of planocellular cancer or adenocarcinoma the irradiation is limited by dose 40-45 Gy during 4-5 weeks with the following surgical removing the tumoral residual.
At the dose choice it is necessary to take into consideratioot only the histological structure of the tumor, but also the peculiarities of its growth. The fast-growing neoformations are more sensitive to ionizing radiation, than the slowly growing ones. Exophytic tumors are characterized by the greater radiosensitivity than endophyticones, infiltrating the surrounding tissues.
The efficiency of biological action of various ionizing radiations is not similar. The above- mentioned doses are specified for “standard” radiation. The action of X-ray radiation with limited energy 200 keV and with average linear energy loss 3 keV/mkm is taken for standard. The relative biological efficiency of such radiation (RBE) is taken for 1. The gamma-radiation and the bunches of fast electrons have approximately the same RBE. The RBE of heavy charged particles and fast neutrons is much higher tube about 10. The account of this factor, unfortunately, is rather difficult, since the RBE of different photons and particles is not similar for different tissues and fractional doses.
The biological action of radiation is defined not only by the value of total dose, but also by the time of its absorption. Choosing the optimum correlation “dose – time”, it is possible to obtain the best effect in each special case. The given principle is realized by means of crushing the total dose on separate fractions (the single doses). Under the fractionated irradiation the tumoral cells are irradiated in different stages of growth and0 reproduction, i. е. at the periods of different radioaffection. Here it is used the ability of healthy tissues to renew their structure and function more completely than this occurs in tumors. Consequently, the second problem is the choice of correct fractionating mode. It is necessary to define the single dose, the number of fractions, the interval between them and, accordingly, the general duration of radio therapeutics. The mode of classical small fractionating has got actually the most practical spreading. The tumor is irradiated by the dose 1,8-2 Gy 5 times per week to the achievement of intended total dose. The general duration of treatment is nearly 1,5 months. This mode can be used for the treatment of majority of tumors with high and moderate radio sensitivity.
At the large fractionating the daily dose is increased to 3-4 Gy, and irradiation is carried out 3-4 times per week. Such mode is more preferable for radio resistant tumors, as well as for neoformations, the cells of which have high ability to renewal of sublethal injuries. But at the large fractionating the radiation complications occur more often than at the small one, especially within the remote period. With the purpose of increasing the efficiency of treatment the fast-proliferating tumors is used the multifractioning. The irradiation is conducted twice a day in dose 2 Gy with the interval not less than 4-5 hours. The total dose decreases by 10-15%, but the course duration shortens by 1–3 weeks. The tumoral cells, especially hypoxic ones, do not have time to be restored after sublethal and potentially lethal damages. The large fractioning is used, for instance, for treatment of lymphomas, midget-cellular cancer of the lungs, tumoral metastases into the cervical lymphatic nodes. The mode of hyperfractioning is used for treatment of slowly growing neoformations. The daily dose of irradiation 2,4 Gy is divided into 2 equal fractions. The irradiation is conducted, accordingly, twice a day, but the daily dose is more than at the small fractioning. The radiation reactions are not marked strongly, in spite of increase the total dose by 15-25 %.
The special variant is so-called split course of irradiation. After brining the half of total dose (usually about 30 Gy) to the tumors do the break for 2-4 weeks. Within this time the cells of healthy tissue are restored better, than tumoral ones. Besides, in connection with tumors reduction the oxygenation of its cells increases.
At intratissue radiation influence, when the radioactive sources are implantated into the tumor, it is used the unceasing mode of irradiation within a few days or weeks. The advantage of such mode is an influence of radiation on all the stages of cellular cycle. It is known that the cells are the most sensitive to irradiation in the phase of mitosis and a little less in the phase of synthesis. In the phase of rest and at the beginning of postsynthetic period the cellular radio sensitivity is minimum. At the distance fractioning irradiation is also used the different sensitivity of the cells in different phases of the cycle. With this purpose the chemical preparations (5-fluoruracil, vincristan), were injected to the patient for delay of artificial cells in the phase of synthesis. Such an artificial accumulation of the cells in the tissue in the same phase of cellular cycle is called the cycle synchronization. Thereby, many variants of crushing the total dose are used and it is necessary to compare them basing on the quantitative indices. For estimation of biological efficiency of different fractioning modes F.Ellis has offered the concept of nominal standard dose (NSD). NSD is the total dose within the complete course of irradiation, at which the essential damage of normal connective tissue does not occur. The NSD volume is fixed empirically at each medical establishment and for each radio therapeutic device.
2.2.2. Physical and chemical means of radiomodifiction.
The efficiency of radiation influence can be raised by means of amplification of radioaffectioning the tumor or weakening the radiation reactions of normal tissues. A number of physical and chemical factors is used for this purpose. They are radiomodifying agents.
The success of radiotherapeutics of the tumors is closely connected with above-mentioned oxygen effect. The oxygen effect is considered as the dependence of radiation biological reactions on the oxygen supply of the cells, and exactly the lowering of their radio sensitivity at the reduction of oxygen content. At the irradiation by heavy charged particles or neutrons the oxygen effect practically is of no importance, but for the rest types of ionizing radiation it is highly essential. There are two ways of the oxygen effect application in radio therapeutics: the increase of tumor oxygenation or reducing the oxygen content in healthy tissues (their hypoxia). The first way causes the increase of tumor radio sensitivity, and the second one – causes the aggravation of stability (radio resistance) of the normal tissues. For increasing of tumor oxygenation the patient is irradiated under the conditions of high oxygen pressure. It is by realized placing the patient into altitude chamber. The healthy tissues are optimum oxygenated. So, the increase of its content in blood plasma does not intensify their radio sensitivity. As concerning the hypoxic tumoral cells, the oxygen diffusion in these cells occurs and their radio sensitivity increases.
The technical realization of oxybaroradiotherapeutic methods requires the combination of altitude chamber and radio therapeutics device, since the oxygen shows sensibilizating action only at the moment of radiation influence. Oxybaroradiotherapeutics turn out to be especially efficient at the treatment of tumors of the head and neck. For reduction of radio sensitivity of the normal tissues during irradiation resort to inhalation by the patient the hypoxic mixtures, containing about 10% oxygen. The patient inspires the mixture by means of common mask, connected with anesthesia device. The gas analyzer constantly checks the mixture composition. Such strategy of treatment is called hypoxic radio therapeutics.
As radio modifying agents are used chemical compounds raising the tumor sensitivity to radiation. To such compounds belong the electronoacceptor substances; among them metronidazole and misonidazole are practically used. Imitating such oxygen function as its relationship to electron, these compounds selectively sensitize the hypoxic tumoral tissues, raising their radioaffection. Unfortunately, both remedies have high toxicity (especially mizonidazole).
However, even per oral taking of metronidazole in dose 6 gr/m2 provides such its concentration in the blood at which it is marked the radio sensitizing effect. As far as possible the application of tampon with metronidazole is added on the tumor area. The artificial short-term hyperglycemia and hyperthermia turned out to be the more perspective modifiers at radio therapeutics. The best effect is obtained at their combination: primarily is carried out the irradiation, after which immediately follows glucose loading, and then is accomplished the tumor hyperthermia. The main factors of increasing the irradiation efficiency are the blood flow suppression, the reduction of intracellular рН, leveling of the cells by the phases of cellular cycle. The tumoral cells, as compared with normal ones, have the ability to intensive glucolysis, i. е. biological splitting of glucose with formation of the lactic acid. The microcirculation disbalance also promotes the retention of lactic acid in the tumor. As tumor exceptionally actively absorbs glucose from the blood, its introduction into the patient’s organism causes its more rapid accumulation in tumor – the temporary tumor hyperglycemia. For maintaining of hyperglycemia during 3 hours is required 230-520 gr of glucose at average glycemia level about 25 mmol/l.
Hyperthermia also belongs to the agents, potentiating the radiation effect. The first International symposium covering this problem was held in Washington in 1975. During the last years were developed the systems of tumor heating and checking of its temperature. The local heating is carried out by means of generators of electromagnetic radiation in MW-, UHF- and HF-ranges. The radiation with frequency 3-16 MHZ is practically used for deeply located tumors. It is possible to warm up both superficial neoformations, and those ones located on any depth. Aerials-radiators were created for intracavitary heating (for instance, rectal tumors). The tumor temperature is supported at the level 42-440 С during an hour. Thermocontrol is realized by means of catheter semiconductor sensors or invasive thermosensors-termistors on the base of injectioeedle. Heated during the hyperthermia skin surface is cooled by means of special gaskets. The independent therapeutic potential of hyperthermia and hypoglycemia is not big. Besides, at MW-hyperthermia the reactions are marked slightly better. But in combination with irradiation it is reached the essential effect, especially at radio resistant tumors, not surrounded with thick fatty layer (to avoid its overheating). Combining the irradiation (under the usual conditions or at the inhalation of hypoxic gas mixtures) with short-term hypoglycemia (2-3 hours) and local microwave hyperthermia and if it is required complementing this complex by surgical interference, it’s possible to obtain the best result even in patients, which were recently considered incurable.
The combination of various radio modifying influences, so-called polyradiomodification, is the perspective way of the further development of radio therapeutics of malignant tumors.
3. THE CLINIC-DOSIMETRIC PLANNING OF RADIOTHERAPEUTICS
Numbers do not control any world, but indicated how to control it.
V. Hеtе
Many factors effect the result of treatment: localization and stage of tumor development, its structure, applied type of ionizing radiation, selected total dose of radiation and its distribution in time. But independently on the type of technical device and the origin of used radiation exists the only defining principle of radio therapeutics. Basing on it the treating tactics and the ways of its realization are chosen.
The main rule of radio therapeutics of the tumors consists in maximum concentration of irradiation energy in tumoral tissue at maximum reduction of dose in surrounding unaffected tissues and in the whole organism. So, the main clinic-dosimetric task is the creation of the most favorable spatial distribution of intended absorbed radiation doses in the patient’s body both for the whole treatment course, and for the each separate irradiation.
Developing the dosimetric plan of treatment, radiotherapeutist and engineer-physicist have the information of two types: a) data concerning irradiated volume and desired absorbed dose in it; b) radio physical features of available radio therapeutic devices.
3.1. The choice of absorbed dose and its distribution in irradiated volume.
For each neoformation radiotherapeutist marks the necessary dose of radiation, following the above-mentioned radiobiological regularities and the results of the patient’s examination. Striving to irradiation optimization, exportable the maximum tolerant dose (D) is usually calculated. It is determined for any irradiation rhythm by special formula.
The knowledge of anatomy of irradiated area and the tissue structure in irradiated zone is necessary for planning the treatment. The tumor position in the patient’s body is exactly defined by means of roentgenography, sonography or CT.
Then the schemes of body section at the “target” level, so-called topometric scheme, are made (i. е. clinical topometry is performed). Basing on roentgenograms in direct and lateral projections it is possible to make transverse (axial), sagital and frontal topometric scheme. In majority of cases are used the schemes of transverse body section. The transverse “cut” is made at the level of the tumor centre, but at the extensive neoformations it is made on two or three levels. To reproduce the body sizes and outlines on the selected level, it is possible to mark the projections of the tumor centre on patient’s skin in two mutually perpendicular projections at roentgenography and then by means of leaden tape to model the body perimeter and to mark the points of projection son the tape. Received drawing is copied onto the paper. Special simple instruments have been developed with the same purpose.
But, certainly, the best way of topometry is the performance of computer tomograms of irradiated area. The specialist, creating the dosimetric plan, has to know not only the tumor localization and volume, but also the tissue structure by the whole body section. Computing complex (CT-+- COMP.) gives three-dimensional picture of dose field and imitates the dosimetric plan of treatment with total inaccuracy not more than 5 %. The image of all the tissues, surrounding neoformation and, in particular, the most sensitive to radiation organs, so-called critical organs is the best advantage of tomograms. The critical organs for head and neck are considered brain and spinal cord, eye, organ of tumor, for thorax – spinal cord, lungs and heart, for abdomen – kidneys and spinal cord, for pelvis – urinary bladder and rectum. Besides, for all body areas the critical organ is skin.
To have an imagination concerning the distribution of the absorbed doses in irradiated medium, the isodose curves are inflicted on topometric schemes and, thereby, the isodose chart is obtained. Isodose lines connect the points with the similar indices of absorbed dose. Usually not absolute indices of absorbed doses (they, as it is known, are expressed in greys), are registered but the relative indices – percentage of maximum absorbed dose, taken for 100%. In radiotherapeutical practice the dose distribution is considered to be acceptable if the whole tumor is concluded into the zone 100-80 % of isodose. Zone of sub clinical tumor spreading and regional metastatic spreading is within 70-60 %, and healthy tissues – not more than 50-30 % of isodose. There are atlases of standard dosimetric plans for distance, intracavitary and combined irradiation in radiological departments. These atlases give the standard isodose charts, drawn basing on measurements in homogenous tissue-equal medium. Water is reasonable to be used as such a medium due to its similarity to soft tissues of human body. But standard dose distribution is always corrected according to the patient’s isodose chart to carry out the individual calculation. It is clear that the dose distribution in the body of each patient differs from phantom one because of different anatomotopographical correlations, tissue density and size, tumor configuration and other individual deviations.
3.2. Radiation-physical description of radiation pencils
When scheduling the irradiation plan an engineer-physicist takes as the basis the primary dosimetric information concerning radiation of radio therapeutic devices available in the department. All these devices are always provided with the set of isodose chart for typical geometric conditions of irradiation. For the description of radiation output of radiator use the definition “exposure dose”. It means the amount of energy to be absorbed from the given bunch in the unit of air mass.
The comparative analysis of isodose charts of different radio therapeutic devices allows to make a number of conclusions to be important for irradiation planning. So, X-ray radiation of low and average energy, i. e. generated at the anode voltage 30-200 kV, causes the maximum of absorbed dose on the surface of human body. Consequently, skin is irradiated most of all. In the deep tissues the dose continuously and fast decreases. At the anode voltage 40 kV the dose at the depth of 3 cm only 10 % of the surface dose. Naturally, at the anode voltage 200 kV radiation penetrates deeper. But here exists quick and sharp reduction of absorbed dose: at the depth of 10 cm remain only 20 % of surface dose. At the deeply located tumor the main part of energy is absorbed not in “the target”, but also in the healthy tissues. Additionally, many diffused rays to be absorbed in healthy tissues appear because of small energy of photons.
The X-ray radiation is intensively absorbed in the bone tissues that can cause the damage of bone and cartilage. So, roentgenotherapeutic devices are used only for irradiation of superficial neoformations.
The Gamma-devices, charged with 60Co, emit nearly homogenous bunch of photons of relatively large energy (1,17 and 1,33 МeV). Maximum of absorption moves 0,5 cm deeper that reduces the skin irradiation. Not less then 50 % of the surface dose remains at the depth of 10 cm. Consequently, the relative depth doses are higher than at the usage of roentgenotherapeutic devices. Additionally, the absorption of gamma-radiation in soft and bone tissues differs a little. The inhibitory radiation of high energy has many advantages as compared with gamma-radiation. In particular, at the energy of photons 25 МeV maximum of absorbed dose is at the depth of 4-6 cm from the surface of the patient’s body. Tissues, disposed before this level, get not more than a half of maximum dose. But the inhibitory radiation has one disadvantage comparatively slow decline of dose after maximum. This means the essential irradiation of tissues behind the tumor. The linear accelerators also produce the bunches of high-energy electrons. In this case maximum of absorbed dose is defined at the depth of 1-3 cm, after that the dose rapidly decreases and at the depth of 10 cm to the tissues are practically not irradiated. This is very farouble for neoformations, disposed not very deeply. But for irradiation of the deeply located tumors the special value possess the bunches of heavy charged particles (the protons, alpha-particles, negative py-mesons – pions). The protons of high energy up to the stop moment move in tissues practically rectilinearly. They are gradually slowed in the substance. Moreover, the linear loss of energy (LLE) increases, reaching maximum at the end of the run. If the bunch consists of protons of approximately similar energy, they have the equal length of run and maximum of energy absorption develops at the end of the way. This sharp maximum is called the Breggs peak. As protons are slightly scattered in the tissues, it is possible to conduct the irradiation with very thin bunch. Such bunch can selectively destroy the areas less than 1 cm3 inside the human body (for instance, hypophysial tumor). Orientating on the intended absorbed dose and the chosen type of radiation, the engineer-physicist plots on the topometric scheme of the body section calculation data – percent deep doses in “the target” and surrounding tissues and organs. As compared with the standard charts of isodoses from the atlas he has to introduce a number of adjustments: for “target” volume and its configuration, curvature of body surface in the given area, heterogeneity of the tissues. In particular, it is necessary to take into account the presence of air accumulation (for instance, in pulmonary tissues, in larynx), etc. A choice of direction of radiation bunches, number and volume of input fields an important is moment. Only at the small surface formation it is possible to obtain the necessary absorbed dose through one field (by means of laser radiation or low-voltage roentgenotherapeutics). It is reasonable to treat some tumors of small volume by means applicators with set of radioactive preparations located above them. But in most cases roentgenotherapeutics is carried out by means of “target” irradiation from several fields. Sometimes the fields of complex configuration (“figured”) are chosen.
In this connection the engineer-physicist has to fulfill a number of calculations, choosing the optimum direction of radiation bunches, distance from the source to body surface, subsidiary devices, forming the required bunch section.
The creation of computer programs was a significant step in dosimetric planning. They allow defining the optimum irradiation conditions basing on the clinical task, adapted personally to each patient. Computer enables to determine the minimum of irradiation fields and their most profitable orientation. At the combination of computer and tomograph the calculation of dosimetric plan is performed in the fractions of a second. Moreover, the engineer-physicist or radiotherapeutist can interact with computer by means of the light “pencil” matching the different variants of irradiation.
4. TECHNOLOGICAL PROVIDING OF RADIOTHERAPEUTICS
There are a great variety of technical facilities in radiological centers and departments. They are intended for treatment of patients by various quantum and corpuscular radiation. According to the nature of radiation source these facility are divided into two large groups: 1) electro physical devices; 2) radioactive preparations of the locked and open type. The complex of technical devices and adjustments for reception of radiation and for their implementation into medical practice is called radiation therapeutic technique. Radio therapeutics is conducted in specialized radiological departments and radio therapeutic cabinets. Radiological departments are functioning in the network of international and republican ontological and radiological research institutes, as well as at the large oncological dispensaries and in regional hospitals.
Radiological departments is the complex, containing blocks for distance irradiation, for using the locked radioactive sources, for diagnostics and treatments by open radioactive preparations, cabinets for planning the radiation treatment and radiation dosimetry, as well as the hospital for patients. In big radiological centers it is advisable to have several medical accelerators, allowing to obtain the inhibitory radiation and bunches of fast electrons of different energy. One medical accelerator provides the attendance of the region with 1,5 mln. inhabitants according to calculations of R. V. Sinitsyn.
The organization of radiological departments is connected with great expenses for complex radiological equipment and defensive buildings. So it is advisable to organize the departments with big bed fund. As concerning the special cabinets of radio therapeutics they exist only in some clinical institutions to perform the radiation treatment of non-tumoral diseases. In any case radio therapeutics should be carried out only in conditions of well-adjusted radiation control. It must provide the standards of radiation safety and constant information concerning radiation situation in the working premises of the departments, sanitary-defensive and observed zones, as well as strict keeping to the established rules of work with sources of ionizing radiation.
4.1. The distance irradiation
Electrophysical generators of ionizing radiation (the medical accelerators), gamma- and roentgen therapeutic devices are used for the distance irradiation of the patients. The block of distance irradiation is disposed in separate building or in isolated part of medical building. The special requirements of radiation defense should be followed at the construction and equipping the cabinets for radio therapeutic activity. Exploitation of devices is allowed at the registration of sanitary passport, which is given by the local organs of State sanitary control.
All radio therapeutic devices provide simple and accurate direction of the working bunch onto irradiated object. Computers allowing conducting the irradiation by the given program in automatic mode equip many of the devices. The front door of the cabinet has electric blocking; it is impossible to open it at the moment of patient’s irradiation. There are telephone and television devices for relationship with the patient. There is a light indicator panel with the sign of radiation danger at the entrance, and the sensors of dissymmetric control are placed inside the cabinets. During the last years medical linear accelerator becomes the leading instrument for distance irradiation. It generates the bunches of photons or electrons of high energy. Accelerator is provided with radiation head, which allows forming the irradiation fields. With this purpose are used special devices – collimators, which have tungsten targets and filters of radiation for brake radiation, and diffusing foil for electronic bunch. There is a diaphragm, consisting of tungsten bars in the lower part of radiation head. Moving them it is possible to create the field of irradiation of different size. As it was already mentioned, the treatment by bunches of high energy from electro physical generators, has a number of advantages. With their help it is possible to convey much larger dose of energy to the target, surrounding healthy tissues are saved from undesirable irradiation. So gamma-therapeutic devices gradually change linear accelerators. But gamma-devices still dominate in oncological dispensaries.
At present two types of such devices: “Rocus-M” and “Rocus-АМ” for mobile methods of radiation therapy and devices of series “Agate” for static, mobile and intracavitary therapy are manufactured by national industry. Gamma-device consists of the following main parts: radiation head, stand, on which it is fastened, table for the patient and control panel. The source of radiator – preparation 60Co with high activity is located in radiation head. There is a diaphragm, consisting of tungsten blocks in the lower part of the head. By means of diaphragm distance control an operator forms the necessary fields of irradiation. Depending on device construction the head allows realizing both static and mobile irradiation. The table for patient has the mobile cover, which can be easy moved in all directions manually or automatically. This allows directing accurately the working bunch on any area of surfaces of patient’s body. The radioactive preparation moves into on-position by the signal from control panel and the process of irradiation begins. The time relay automatically switches off the device and stops the irradiation at the expiration of the planned period. The radioactive preparation is simultaneously transferred into position of keeping. For programme management the gamma-devices are created the special systems (for instance, system “Altay-МТ”). In these cases the whole mode of irradiation is assigned and checked for each patient individually. The main type of roentgenotherapeutic devices, used in radiation therapy is shot-focal one. Such devices are intended for irradiation of pathological centers, mainly tumors, located on the body surface or on mucosa of hollow organs, from short distance. The shot-focal devices are provided with two or three X-ray tubes, which work at voltage from 8 to 100 kW. So, the device RUМ-21 has three tubes. Anode in the main tube has lateral outlet of the radiation bunch through beryllium window. Irradiation is conducted from the distance 1,5-5 cm. There is a set of tubuses of different shape and sizes, by means of which the size of irradiated field is limited and the constancy of distance from source to body surface is provided. Two other tubes with caring-out devilled anode and with carried-out cone anode are used for intracavitary therapy. It is possible to introduce caring-out anode into the hollow organs: oral cavity, rectum, vagina for irradiation the focus on mucous. In some scientific and medical centers for radiation therapy are used the accelerators of heavy charged particles: synchrocyclotrons for reception of protons and cyclotrons for neutron radiation. Such accelerators are the complex engineering-technical construction, equipped by special electro physical equipment. They fulfill the independent medical program besides of different physical investigations. The medical tract is created for realization of this program.
4.2. Contact methods of irradiation
Contact methods of irradiation mainly are carried out by means of locked radioactive sources and in very limited boundaries – open radioactive preparations. Under the locked radiation source (the locked radioactive preparation) is meant the radioactive substance, comprised in such membrane or existing in such physical condition, under which is excluded the substance spreading into surroundings.
The needles and drains with 137Сs (the energy of gamma-radiation is 0,66 MeV, period of half-life is 30 years) and preparations 60Co (the energy of gamma-radiation is 1,17 and 1,33 МeV, period of half-life is 5,26) are most often used as locked sources. Radium preparations, radioactive iridium wire, cesium balls, preparations of radioactive gold etc. are also used. As open sources use per oral application of 131I, intravenous introduction of 32Р and intracavitary introduction of the colloidal solution of radioactive yttrium.
The block of locked radiation sources includes the special premises and hospital rooms (physicians’ and nurses’ cabinets, pantries etc.). The depository of radioactive preparations, radio manipulation room, procedural room, radiological operating, roentgen diagnostic room, room for hose gamma-therapeutic device, permanent establishment for patient (with “active” beds), discharging room belong to special premises. The premises for work with radioactive preparations are marked with the sign of radiation danger. We’ll analyses the whole chain of technological providing of the contact methods of irradiation. The defensive safes, containing the radioactive preparations, are located in the depository. By means of transport tape they are sent from here into manipulation room, where they are prepared to application. By means of distance instrumentation the preparations are introduced into radio carrying device on defensive manipulation table. The adjustments, beloning to the last, (applicators), endostats and colpostats, moulages and masks, made from plastic, are placed on the skin or mucous surface. The personnel works in manipulation room behind the defensive screens, in defensive aprons and gloves. Antiseptics sterilize applicators. Radio carrying devices are sent by pipeline or on defensive truck and in defensive boxes from manipulation room into procedural room, where the radiation courses are fixed on the patient. For performing the intratissue irradiation preparations are transported into radiological operating room. Both procedural room and operating one are provided with all the necessary defensive equipment. After installing or introduction of radioactive preparations their location in tissues or body cavities is checked by means of roentgen television X-raying. The X-ray device is better to be assembled with procedural or surgical table. Then the operator can control the introduction of preparations on television screen. Otherwise, the patient is taken into nearby X-ray cabinet. Having made sure in the right location of radio carrying devices, the patient is transported into hospital. There he is accommodated in a separate defensive ward or in a small general ward with defensive fence of the bed. Each bed is equipped with the telephone or video television device for controlling the patient. Removing the sources of irradiation is carried out in special discharging room. In accordance with “Main sanitary rules of work with radioactive substances and other sources of ionizing radiation the requirements of radiation safety are strictly kept in blocks of locked and open sources. The collection, keeping and nuclear disposal are well organized. In the departments with open radioactive substances the air from closets and boxes is purified on special filters.
Maximum possible dose of radiation, equal 50 мZv/year, got by the whole body, gonads, red bone marrow, was established for personnel.
Intracavitary gamma-therapeutics, as well as applicative and intratissue radio therapeutics is performed in the block of locked sources. Intracavitary method of irradiation is intended for bringing of high-absorbed dose to the tumor, located in the wall of caval organ, at the maximum sparing of surrounding tissues. The main preparation for intracavitary gamma-therapeutics is 60Co. The preparations of this radionuclide have the form of cylinders or balls, covered with a thin layer of gold, which absorbs beta-radiation of cobalt, but misses its gamma-radiation.
The special adjustments – applicators or endostates are used for fixation of preparations in irradiated cavity (the oral cavity, cavities of rhino pharynx, uterus, vagina, rectum). Each applicator consists of one or several hollow metallic tubes. Gynecologic applicator, for instance, has 3 tubes. The central tube is curved according to the uterus form and is introduced into its cavity. Two other tubes, finishing iozzles, made of organic glass, are introduced into the lateral vault of the vagina. The correct location of applicator is checked at the X-ray examination. Then the radioactive preparations are introduced in to applicator manually or by means of automatic devices. They are placed linearly or in volume (“linear” and “volumetrically” sources). After that the roentgenologic study is performed once again to make sure in optimum location of preparations. Besides radioactive cobalt, being the source of gamma-radiations radio nuclide californium – 17Сf is used for intracavitary therapeutics. It is a source not only of gamma-radiation, but also of neutrons with energy 2,35 МeV. The neutron irradiation has a high biological activity. Besides, the oxygen effect is of no importance at the interaction of neutrons with tumor tissues. The results of irradiation doses not depend on oxygen concentrations in tumor cells. So, neutron intracavitary therapeutics is especially useful at the tumors, resistant to gamma and inhibitory radiation.
At present the optimum variant of performing the intracavitary irradiation is the application of hose therapeutic devices. The variety of such devices has been created for treatment of tumors of uterus, rectum, urinary bladder, oral cavity and esophagus. The hose device enables to perform the procedure of treatment in two stages. At first into the organ cavity is administered the applicator and is checked its location by roentgenological method, and then the radioactive sources are administered into applicator through the hoses (the method of consequent introduction). Consequently, the irradiation of personnel during this procedure does not occur. Such a method of irradiation has got the name auto loading. An application method is one of the types of contact irradiation. The locked radioactive preparations are placed on the superficially disposed centers of affection. The preparations are located in the moulage in that way the tumor would be irradiated uniformly.
60Co, 137Сz, 192Tr are used as radioactive sources. The system of location of radio bearing tubes has been elaborated by the English scientists and is known as Manchester system. The method is used for small skin and mucous tumors spread in the tissues no deeper then 1-2 cm. The other type of contact influence is intratissue method of irradiation at which the radioactive preparation is introduced directly into the tumor tissue. Its irradiation occurs continuously and because of that the influence on tumor cells seizes all the phases of cellular cycle, including the most radiosensitive ones. Additionally, the preparation localization in the tumor provides the high dose ieoformation at relatively small irradiation of surrounding tissues. According to the type of radiation distinguish intratissue gamma-, beta- and neutron therapeutics. For constant implantation use radionuclides with short half-life – 198Аu, 90U, 125I, with relatively low radiation energy. The preparations are manufactured as granules, covered with gold or platinum. They are introduced into the tumor by special installators. The implantation of radioactive preparations into the tumor for temporary irradiation is carried out in two ways: manual introduction or above-mentioned method of consequent introduction at which intrastate (plastic tubes of different shape) are primarily introduced into the tumor. Having disposed the tubes in the intended order, the active sources (60Co, 137Сz and others.) are introduced into their lumen manually or by means of the hose device. The suitable source for intratissue therapy is made of radioactive iridium, which is introduced into preliminary implantated nylon tubes. The radio bearing tubes with californium are used for treatment of radio resistant tumors, as a source of neutron radiation.
Introduction of radioactive preparations into the tumor tissue is a surgical interference and it should be performed in aseptic and antiseptic conditions. The strict keeping to above-described rules of radiation defense is necessary. But there is a special method of intratissue irradiation directly on the operating table. At such a radio surgical method the tumor is removed within the healthy tissues, and intrastate is left in the wound for the following introduction of radioactive preparation. If surgical removing of the tumor is impossible, the radioactive sources with short half-life are introduced into its tissue after opening the caval organ, laparotomy or thoracotomy. In the last years the other strategy of intraoperative irradiations develops. After preoperative course of distance or combined irradiation the intraabdominal tumor is exposed (for instance, the intestinal cancer). The resection of neoformation is performed and then the patient is transported into the cabinet of distance radiotherapeutics. The irradiation should be carried out by electronic bunch. There is a set of applicators of different diameter. To see the tumor residue or its bed, the tubuses are made from plastic. This method provides good dose distribution, as the stomach and intestinal loops can be moved from “the target” and the dose from electronic bunch rapidly decreases, behind the tumor residue or zone of its sub clinical spreading.
At the tumor dissemination on pleura or peritoneum it is possible to apply the introduction of colloidal solution of radioactive yttrium or gold into serous cavity. Such a palliative treatment is mainly directed on the annihilation accompanying pleurisies or ascites.
5. THE COURSE OF RADIOTHERAPEUTICS
Different physicians send the patients to the radiation treatment: oncologists, surgeons, therapeutists, dermatologists, endocrinologists, gynecologists and others. The patient must have a direction or case record. These document contain the short clinical data, diagnosis, instructions on the previous treatment, as well as indications for radio therapeutics. The radiotherapeutist internist must be sure in proper diagnosis. For this he is obliged to study carefully the case record, to examine the patient, to compare the data of study with laboratory ones, to pay a special attention on the condition of blood and bone marrow. In the case of insufficient information the radiotherapeutist prescribes the additional examination. It should be ascertained if the patient had been undergone radio therapeutics before. If it took place it’s necessary to know all the details (time and method of radiotherapeutics, irradiated parts of the organism, the total dose complications). It is impossible to rely only upon patient’s information. The extract from case record or written health certificate from medical institution is needed. This is important because the repeated irradiation is possible only after 60-70 days after the first one with regard for conditions of the previous irradiation. However, it was already indicated above that the efficiency of the repeated courses is low. The first course should be maximum radical and as far as possible a single one.
As a result of a detailed patient’s examination the oncologist, radiotherapeutist and chemotherapeutist (and often therapeutist and hematologist) elaborate the coordinated strategy of treatment. It depends on tumor localization, its sizes, histological origin and stage of development.
The small tumor can be successfully removed both by the surgical and the radiation method. The choice here depends mainly on localization of neoformation and possible cosmetic consequences of the operation. Additionally, it should be taken into account that tumors in different anatomical areas differ by their biological features.
Carcinomas of skin, lip, rhinopharynx, larynx, mammary gland, uterine cervix, endometrium, prostate as well as retinoblastomas, medulloblastomas, seminomas, ovarian dysgerminomas localized lymphomas and lymphogranulomatosis belong to radiocurable tumors. Of course, the success can be reached on the relatively early stages of tumor growth. Radiation destruction of the big tumor runs across almost insuperable difficulties because of radiation damage of its vessels and stroma with the consequent radiatioecrosis. Combined treatment is used in these case. The combination of radiation influence and surgical treatment has the good results at Wilm’s tumor and neuroblastomas in children, at the treatment of cancer of sigmoid colon and rectum (so-called colorectal cancer), at embryonic ovary cancer, rhabdomyosarcomas, sarcomas of soft tissues.
Surgical treatment is very important for removing the tumor residue after radiation treatment. On the other hand, radiation therapeutics is indicated at the relapse of malignant tumor after surgical or combined treatment (the relapse of carcinomas of skin, lower lip, uterine cervix), as well as at the local metastases into lymphatic nodes, bones and lungs.
5.1. Preradiation Period
Preradiation period is a period of the patient’s preparation to the treatment. It should be started with psychological preparation. The patient is explained the necessity of radiation influence, its efficiency, pointed the possible changes of general state and some radiation reactions, regimen dietary peculiarities. The сconversation with the patient must inspire him with hopeness and confidence in the results of treatment. The further stages of the patient’s preparation are high-caloric diet with intensive drinking, the organism’s saturation with vitamins (in particular, not less 1 gr of vitamin C per day), sanation of irradiated surfaces and cavities. The skin in irradiated areas must be clean, without excoriations and pustules. All the physiotherapeutic procedures and external medicamentous preparation, ointments, mashes etc. are abolished. At the irradiation of facial parts of the head perform the sanation of oral cavity. Alcohol drinks and smoking are forbidden. At the accompanying inflammatory process the antibiotics are prescribed, but at the anemias prescribe the remedies of its correction. Clinical topometry is the next main stage. It is described above. It is necessary to emphasize once again that computer and magnetic-resonance tomograghy create new possibilities of the maximum accurate laying of radiation bunches onto “targets”. The transition from the analysis of “targets” location on the plane to three-dementional apprehending of the tumor, from anatomical information – to geometric imagination, to development of complex dosimetric distribution provided by computer programs take place.
Basing on clinic radiobiological analysis and topometry choose the proper type of radiation and physic technical conditions of irradiation for absorption of intended amount of energy in tumor at maximum dose reduction in surrounding tissues. In other words, it is determined the optimum total absorbed dose of radiation, single dose (the dose from each irradiation), general duration of treatment.
The clinicist and engineer-physicist has to solve many problems during the preradiation period. They choose the distance, contact or combined irradiation taking into consideration the topographoanatomic peculiarities of the tumor and its histological structure. It is defined the technology of irradiation and the types of applied device, to be used. The condition of the course (dispensary or stationary) is discussed with the physician. The physicians on dosimetric planning together with engineer-physicist mark the optimum distribution of the fields for distance irradiation. The static irradiation can be conducted through one inlet field on the body surfaces (the single-field irradiation) or through several fields (the multi-field irradiation). If the fields are located above the different sides of irradiated area such a way that the tumor is in the crossing of radiation bunches, it is considered the multi-field cross irradiation. It is the most spread method of irradiation. It allows raising significantly the focal dose as compared with the dose iearby organs and tissues. The choice of amount, localization, form and value of the fields is strictly individual. It depends on the type and energy of radiation, required single and total doses and tumor size, size of the zone of its subclinical spreading. Two opposite fields, three fields (one anterior or posterior and two lateral), four fields with crossing in the center bunches are used more often. At the mobile irradiation the source of radiation moves relative to the patient. Three ways of mobile irradiation: rotatory, sectional and tangent are the most spread. At all these ways a bunch of radiation is directed onto the tumor. In the case of rotation the irradiation is performed on the whole perimeter of the patient’s body. The advantage of this method is a concentration of absorbed dose in the focus of affection with simultaneous decrease of the dose in surrounding tissues and especially in skin. But integral absorbed dose in the patient’s organism is significant. The rotatory method should be conditionally considered as the final variant of multi-field cross irradiation, when the amount of fields is extremely large. The method is indicated at the tumor localizatioearby the mean body axis (for instance, at the esophageal cancer). At the section irradiation the source moves relative to the patient’s body by arc within the chosen corner – 900, 1200, 1800. Such method is reasonable to be used at the eccentric tumor location in the patient’s body (for instance, at the cancer of the lung or urinary bladder). At the tangent irradiation the center of system rotation is on the small depth under the body surface. So, the bunch from the moving source all the time is directed by tangent relative to the irradiated part of the patient’s body. This is reasonable at the irradiation of superficially located focus with large length (for instance, at the dissemination of cancer nodules in the skin of thoracic wall after the mammary gland removing). Preradiation period is completed by the final registration of medical plan. The medical plan is the set of documents of clinicoradiobiological and clinicodosimetric planning, containing both the chart of dose distribution in the patient’s body, and roentgenograms, performed through inlet fields and confirming the correctness of direction of radiation bunches on the focus. Before the beginning of radiation period it is necessary to fulfill the marking-out of the irradiation fields on the patient’s body. For this purpose the patient occupies such a position in which he will be during the medical irradiation. Then the direction of radiation bunch onto the tumor is performed (of course, the device herewith is not switched on and irradiation does not occur). The central axis of the bunch must pass through the center of inlet field and the tumor center. So, the laying onto the focus at the static methods of irradiation is called centration. Centration is possible to be realized by means of mechanical device (tubus localizator, arrows-indicators or pivots connected with radiation head). The more suitable are the optical methods of centration: light bunch is rejected by the mirror toward the bunch of ionizing radiation and illuminates the field on the surfaces of the patient’s body. This light field is combined with marked on the skin planned field and light reflection, directed perpendicularly from additional centrators. But the most reliable are such roentgenologic devices of laying, at which is done the aiming picture on the film, placed behind the irradiated area by means of working bunch of the device or additional roentgenologic tube. On such a picture the tumor imagination must be in the center of the irradiation field.
During the last years have been created the special devices – simulators for roentgenologic centration. They are called so because they have to imitate (simulate) all the motions of the radiation source. Simulator is the X-ray device, provided with the amplifier of X-ray imaginator and display for the demonstration of imagination. The tube can move by the circumference around the patient. The roentgenologic bunch exactly imitates the medical bunch. The source of light marks the borders of X-ray bunch on the surface of the patient’s body. The physician has an opportunity to control the correctness of the laying onto the focus by imaginaton on the screen. If the computer is available it can correlate the correct direction and the size of radiation bunch by means of a light “pen”.
5.2. Radiation period
The radiation period is a period of the irradiation under the constant medical control. Clinical management of the patient during the radiation and postradiation periods is not less important than the irradiation itself. It allows to mutate the medical plan and to define the necessary accompanying treatment. For the irradiation of each field the patient is in the comfortable position (as a rule it is a horizontal position on the back). Immobilization of the patient is very important. Even his slight motion causes the change of dose distribution. The immobilization is performed by means of different devices. The polyfoam head-supporter is used for the head and neck fixation. The fixing devices should be made of the thermoplastic material individually for each patient. This material is softened in hot water and then is modified for the patient and it hardens quickly.
The correctness of bunch laying is checked by means of simulator or roentgenography (at the last case the roentgenocontrast thin catheters or leaden marks are plotted on the edges of intended field to get their imagination in the pictures). In the process of irradiation the physician or laboratory assistant supervises the patient on the telescreen. The telephone device provides the intercommunication between the physician and the patient. After irradiation the patient is prescribed two-hour rest in the open air or in the ward with good ventilation. The data concerning each irradiation are registered in the case record. So, in the process of treatment a greater attention is paid to the forming of working bunch and its aiming onto the patient. The various subsidiary devices: compensators, clinoid and lattice filters, shielding and splitting blocks are used fos this purpose.
The standard charts of isodoses show the distribution of absorbed energy in tissues when the radiation bunch falls on the irradiated surface perpendicularly to it. But the real surface of the human body in the majority of areas is of spherico-convex shape. To avoid the distortion of the calculated dose distribution, use the compensators, made from tissue-equivalent material (for instance, paraffin). Compensator is put to the body surface to form the flat surface, perpendicular to the axis of radiation bunch.
The clinoid filter allows to change the dose distribution in tissues, as under the thin part of the wedge the absorbed dose is significantly higher than under its extended part.
At the wide-spread tumors the irregular irradiation by means of lattice filters is sometimes used. Such filter is a leaden plate with multiple holes. The radiation hits only on these areas of body surface, which are located under the holes. Under the areas covered with the lead the dose is 3 – 4 times less and is conditioned only by diffused radiation. But at the depth the difference in dose values under the open and locked areas decreases because of the rays dissipation and their dispersing nature. The irragular irradiation promotes the renewal processes in the tissue at the expense of less irradiated areas. It allows to bring relatively large dose to the tumor and at the same time to reduce the reaction of skin and subcutaneous fat on irradiation. At irradiation of the irregular-shaped objects occurs the necessity in the complex configuration of irradiation fields. Such “figure” fields can be obtained with the help of leaden or tungsten shielding blocks . They are placed on the special stands, attached to the radiation head of device. Figure shielding diaphragm made of the leaden blocks used with the same aim. This method manages to protect especially sensitive to irradiation organs: eyes, spinal cord, heart, gonads and others, which can be located nearby the irradiation zones. Sometimes the defensive leaden block is disposed in the central part of the working bunch. It splits the dose field into two half’s. This is reasonable, for instance, at irradiation of the lungs, when it is necessary to protect a spinal cord and heart from irradiation.
5.3. The reactions of the organism on medical radiation influence. Postradiation period.
Radiotherapeutics of the tumors is accompanied by general and local reactions. At the modern technology of irradiation these reactions, as a rule, do not reach the severe stage. However, the physician must know their manifestations and is obliged to take all the measures for their prevention and treatment.
6. BASES OF RADIATION THERAPY OF MAXILLOFACIAL MALIGNANT TUMORS
The cancer of red border of lower lip, mucous membrane of oral cavity, pharynx makes up a little more than 4% of all malignant neoformations. 90% cases of cancer make up planocellular forms and 10% – the other forms of malignant tumors (the cancer of salivary glands, sarcomas, lymphomas, melanomas and others). In patient with the cancer of oral mucosa the radiation therapeutics as independent method is used in approximately 70% cases in combinations with surgical interference – in 15% cases. Only the operative treatment is used in 10% patients. Radiation therapeutics is a method of choice in patients with cancer of red border of lower lip.
At the planning of radiation therapeutics as independent method of treatment in each individual case it is defined the nature of course – radical or with palliative purposes. In the last case it allows to remove or relieve the severe clinical manifestations of disease (pain, disorders of chewing, dysphagia, ahylia, speech, bleedings, scent from the mouth, lockjaw). The total focal dose of palliative course is usually not less than 75% of radical course dose. The majority of patients, even with late stages, but in satisfactory general status, are usually prescribed the radical course. The relative indications to the choice of radiation therapeutics with palliative purposes are senile age, extensive tumoral infiltration of tongue, fundus of the mouth, massive destruction of the jaw by tumor, metastasis, cachexia, recent vascular disturbances (the infarct, insult). However, even in these cases at the favourable response reaction of the tumors on irradiation and its good endurability, the tactics is changed and the radical course is performed.
Sanation of oral cavity should be carried out in the shortest terms before radiation therapeutics. Correct sanation reduces the severity of local radiation reactions of oral mucosa and frequency of such complications, as aspirative pneumonia and radiation osteonecrosis. Peculiarities of sanation in each case are defined depending on method of radiation therapy. So, when planning the radical course of distance gamma-therapy in zone of intensive radiation influence the teeth, treated on cause of pulpitis and periodontitis, are liable to removing .
Radiation therapy can be started within 7-10 days after teeth removing, at intratissue method – after 2-3 days.
During the preoperative course in patients with malignancies of upper and low jaws only teeth rootson on the side of tumor are liable to removing.
Sometimes it is necessary to remove one or more healthy teeth for bringing the tubus of roentgenotherapeutic device.
The radical irradiation is usually conducted from two contrary fields, disposed on both sides of the face, with inclusion of clinically defined tumor.
Split radical course of radiation therapy consists of two stages, separated by fortnightly break. The local radiation reactions on mucosa reduce during the break.
The repeatedly split course of distance gamma-therapy is preferable for softening of local radiation reactions. The total number of stages is determined by the response reaction of tumor and irradiation endurability.
Radiomodifiers or local MW-hyperthermia is prescribed for raising the efficiency of treatment. If during 6 weeks (but not earlier) after completion of radical course the histologically verified tumor remainder is revealed, the specialists discuss the question concerning operative interference.
The combined method of treatment unites the radiation influence and operative interference. The preoperative course, causing the reduction of tumor at the expense of the most sensitive peripheral part, reducing the mitotic activity of tumor cells and the risk of arising the preoperative relapses and metastases is preferable.
The postoperative course is prescribed in the cases when during the operation it was not possible to remove the tumor completely. In such situations radiation treatment considerably reduces the frequency of arising the relapses. The interval before the radiation treatment must not exceed 6 weeks. Otherwise, the efficiency of course reduces.
During the conduction of radiation therapy teeth are covered with protective occlusive blocks made of high hardening plastic for absorption of secondary radiation from teeth and metallic construction appearing at distance gamma-therapy.
Removable dentures are permitted to be used only during the meals before the appearance of local radiation reactions on mucosa.
At the cancer of red border of lower lip is preferable the radiation method of treatment. It is not inferior to operation in efficiency and exceeds it in cosmetic results. The surgical interference and cryodestruction are resorted to at the tumor relapses or at the rare radioresistant forms. The combined method with preoperative course is preferable at germination into the jaw.
At the cancer of different parts of oral mucosa (tongue, fundus, cheek, gingiva, stomatopharynx) in cases of infiltration of only sub mucous layer radiation therapy is conducted as an independent method of treatment. Intracavitary methods (X-ray therapy, treatment on AGAT-B) are preferable.
The combined method, including distance gamma-irradiation with the following introduction of radio bearing needles with 60Co or intracavitary irradiation is preferable at tumor infiltration of below-lying muscles no more than by 2 cm. The combined method of treatment with preoperative course of distance gamma-therapy with the following operation after 4-5 weeks is planned at the more wide-spread tumoral process with involvement the muscles and destruction of bone tissue of the jaw.
At the radiation treatment both the primary tumor and the paths of regional metastasing are affected.
The tactics of treatment of cancer metastases is defined by their sizes, amount, unity with nearby tissues, localization and clinical form of growing and stage of primary tumor.
The combined method with preoperative course, essentially reducing the frequency of relapses, is prescribed to the patients with multiple metastases.
RADIATION THERAPY OF NON-TUMORAL DISEASES
The radiation therapy is rather seldom applied for treatment of non-tumoral diseases. Business isn’t in its small efficiency; on the contrary, it concerns to a number of valuable medical methods. But, first, many non-radiation ways of treatment (antibiotico-, hormonotherapy etc.) have appeared. And, secondly, radiologists collected the data about possible adverse somatic and genetic consequences in the patients who have been especially undergone to irradiation at infant age. Certainly, the probability of the serious remote defeats is insignificant, but it has to be considered at the treatment of diseases, dangerous for the life and can be controlled by means of others therapeutic methods.
But it would be wrong to exclude an irradiation from an arsenal of modern medical means in general. It is proved to be rather useful, and sometimes even indispensable at the treatment of furuncules, carbuncles, hidradenitis, panaritiums, sub acute and chronic trombophlebitis, erysipelatous inflammation, post-operative inflammatory complications (anastomositis, pancreatitis etc.), neuritis and neuralgia, arachnoiditis, postamputating pain syndrome, scapulohumeral or ulnar periarthritis, deforming arthrosis with pain syndrome, calcanel bursitis and some other diseases). The radiation therapy of non-tumoral diseases is used only according to the strict individual indications if the other methods of treatment are inefficient. The radiation therapy of non-tumoral processes at children, teenagers and pregnant women is contra-indicated. At medical application of radiation ionizing radiation are used only the sparing ways of irradiation. The radiation bunch is directed precisely on the pathological center, and radiation is selected so that as little radiation energy as possible would be absorbed in surrounding tissues. The single and especially total dozes should be small in comparison with treatment of malignant tumors. In most cases the radiation influence is supplemented with medicinal and general roborant remedies.
The direct local irradiation of the pathological center to be carried out by a distance method or, much more rarely, by means of beta-applicators is the basic method of radiation therapy of non-tumoral diseases .
Beta-applicators are the flat or bent by the shape of irradiated surface plates covered with a layer of radionuclide or flat boxes containing radionuclides. Beta-radiators: 32Р, 90У, 204Т are applied as radioactive source. For influence on the deeply located centers are used beta-plants, and on superficially located ones — an electronic bunch of the accelerator or short-focus roentgenotherapeutic device. Localization of the center, its sizes and relation to the nearby organs and tissues before the beginning of distance irradiation are precisely determined.
The irradiation fields are marked by the borders of the center, and at inflammatory infiltrates — 0,5-1 сm more. The healthy tissues are protected by special screens or lead coated rubber.
7.1. Inflammatory processes
At inflammatory injuries the irradiation causes local plethora of tissues with increase of permeability of capillaries, amplified migration of blood elements into tissues, decomposition of leukocytes and especially of lymphocytes with formation of biologically active substances.
It is possible to obtain the cessation of the process in initial phase of inflammation. The pain decreases or stops, edema and tissue infiltration disappear.
Accelerated melting of infiltrate and its delimitation are observed at irradiation in the phase of necrosis and suppuration. As a result the tissue decomposition involves the smaller area and the large defects and cicatrices do not appear. The surgical opening the abscess with the following irradiation of surrounding inflammatory swell is reasonable at the suppurative process after one or two irradiations. The irradiation in the phase of regeneration results in more rapid epithelization of the wound.
At the treatment of severe inflammatory foci the single doses are within 0,1 – 0,2 Hy, but the treatment of abscesses they are within 0,3-0,5 Hy. The more severe and diffuse the process is and the more earlier the treatment has been started, the smaller dose must be. Sometimes, it is enough 1-2 irradiations to obtain the successful result. In the other cases carry out 3-5 irradiations. In phase of infiltration the intervals between them are 1-2 days, but in phase of suppuration – 2-3 days. At the chronic current of inflammation the irradiation is repeated after 2-3 days to the total dose 2,5-3,0 Hy, sometimes a little more.
All the thermal and physiotherapeutic procedures, as well as salve dressing are abolished for the period of radiation treatment and rehabilitation. The procedures of irradiation are combined with medicinal treatment. Radiation therapy is not expedient at the developed limited abscesses. It is also contra-indicated at phlegmons in weakened patients.
7.2. Degenerative-dystrophic diseases of osteoarticular apparatus
Radiation influence can not result in patient’s recovering at the degenerative-dystrophic injuries of bone system. But it allows to remove or reduce the pain syndrome and thus to raise the patient’s ability to work. In most cases, the patients are elderly people, in which the danger of radiation genetic consequences is insignificant. The radiation influence upon immunospecific reactions of articular tissues and nerve receptors is in the basis of therapeutic effect. The procedures of irradiation are effective at the deforming arthrosis, vertebral osteochondrosis, bursitis, peritendinitis. They are indicated in those cases, when medicinal preparations, physiotherapy or balneologic treatment are not advisable or have been unsuccessful.
The distance irradiation by gamma-plants or roentgenotherapeutic devices is used for the treatment. The single doses are 0,3-0,5 Hy, the total ones – 3-5 Hy with interfraction interval 48 hours. Sometimes it is possible to use even smaller total doses. The value of fields must correspond to the sizes of irradiated joint or injured motor vertebral segment. Only the end of irradiation course usually reveals the therapeutic effect even during 4-6 weeks after its completion. It must be taken into consideration at estimation of the treating results. The initial exacerbation of the process or, on the contrary, rapid favorable outcome must be not considered as indication to reduction or increase the total dose.
7.3. Some neurological diseases
The problem of radiation treatment depends on the process nature. At the therapy of functional and inflammatory diseases of central nervous system expect the change of functional condition of nerve centers and nodes, reduction of concentration of biologically active substances in them, increase the permeability of hematoencephalic barrier. Due to these processes the status of patient improves, the treatment of inflammation speeds up. At neuritis, neuralgias and radiculites the irradiation of nervious nodes, roots of cranial and spinal nerves, as well as peripheric nervous receptors quite often have a good medical effect. The radiation therapy of syringomyelia requires a special attention. This is a chronic disease of spinal cord, revealing in its growing in gray substances of glial tissue.
New-formed tissue is inclined to disintegration and forming the cavities. As a result, the innervation’s of tissues and organs is disturbed. That is expressed in disorders of sensitivity, motions and trophicity. The young glial cells perish and the development of diseases stops under the influence of irradiation.
It is used the distance irradiation through narrow long fields, disposed by 3-4 cm to the sides from vertebral column at the level of injured parts of spinal cord. The bunch of radiation is directed onto the spinal cord with slopping from each field. The irradiation is conducted every day or every other day in dose 1,5 Hy. The total dose is carried to 10-12 Hy.
The radiation therapy of postamputating pain syndrome is of great importance. As it is well known, many patients after amputation of extremities suffer from severe pain in stump or phantom limb pain, which are perceived as those ones coming from nonexisting (amputated) limb. The stump, corresponding reflexogenic zones, and at the disorders of sympathetic nervous system – its nodes (for upper limb this level is Сз – D11, for lower – D10– S2) are undergone the radiation influence. The irradiation in single dose 0,3-0,4 Hy is carried out with 2-3 day interval. The total dose in the area of stump is 2-3 Hy, in reflexogenetic zones – 1,5-2 Hy, on sympathetic nodes – to 1 Hy. The medicinal facilities and surgical interference on thyroid gland are used at the treatment of thyrotoxicoses. But sometimes is used the radiation influence on thyroid tissue. With this aim the patient is prescribed strictly calculated dose of radionuclide iodine – 131I. To be accumulated in thyroid gland it causes the partial destruction of thyroid cells. The shortcoming of this method is a possibility of over dose 131I and development of steady hypothyrosis. As a result the patient will always need the substitution iodotherapy.
RADIAL REACTIONS AND DAMAGES
5.3. The reactions of the organism on medical radiation influence. (Postradiation period).
Radiotherapeutics of the tumors is accompanied by general and local reactions. At the modern technology of irradiation these reactions, as a rule, do not reach the severe stage. However, the physician must know their manifestations and is obliged to take all the measures for their prevention and treatment.
The expressiveness of the general organism reaction depends on the irradiation area, integral absorbed dose and irradiation rhythm. The greatest reaction is caused by the irradiation of the whole body or its large parts. Smaller changes appear at the same influence on the separate organs (the local irradiation). The reaction is intensive if the organs of abdomen, small pelvis and thoracic cavity are in irradiation zone, and they are much weaker at the influence onto extremities. Division of the total dose into fractions and at conducting irradiation with intervals promotes the reduction of radiation reactions. It should be noticed that the general reaction of the organism is connected not only with the direct action of ionizing radiation, but also with damage of the tumor and absorption the products of tissues disintegration. The general reaction is manifested in the tonus reduction, flaccidity and increased erythrism. The patient is disturbed by the absence of appetite, sometimes, nausea, insomnia or, on the contrary, sleepiness, vertigo, pain in joints. Sometimes occur cardiovascular damages: dyspnea, tachycardia, arrhythmia, hypotension. The symptoms of digestive disturbances: intensified salivation or, on the contrary, xerostomia, pharyngeal smarting, bitterness or metallic smack in the mouth, eructation, thirst, meteorism, stomachache, diarrhea are often registered. The loss of body mass is typical. The objective index of general radiation reaction is the reduction of leukocytes number in peripheral blood shelters. So, clinical blood test should be done every 5- 7 days.
For prevention and weakening the symptoms of general radiation reaction the patient is prescribed high-vitamin diet feeding with sufficient amount of liquids. The medical physical exercises are also of importance. The pharmaceutical complex including antihistamine preparations, antitoxic substances and stimulators of hemopoiesis, especially leucopoiesis, are used. The transfusions of small volume of the same-group blood (100-150 ml) or leukocytic are performed if it is required. The antibiotics are prescribed at the inflammatory complications. The distance irradiation is closely connected with local radiation reactions of the skin and mucosa. Skin reddening (erythema) and dry radiodermatitis belong to the skin reactions .
The light skin reddening is observed during the first hours and days after irradiations and it is explained by the vasomotor disturbances. The stable erythema appears in 1- 2 weeks after beginning of the treatment and is accompanied by the slight painfulness and skin edema in the area of irradiation field. After cessation of radiation influence the skin reddening decreases and it begins to desquamate. Then it is noted the pigmentation, which can exist for a long time.
At the more intensive and long-term irradiation erythema is brighter, edema is expressed better. Cuticle epidermis gets thinner. Dry radio dermatitis develops. It results in cuticle detachment by the whole layers. The skin continue to desquamate for a long time, it remains dry and pigmented.
At the correct strategy of radiation treatment humid radio dermatitis must not develop. The skin is infiltrated; the vesicles, filled with serous liquid, form on it. After cuticle rejection appears humid brightly rose surface with scanty discharges. It gradually epithelizes, but skin desquamates for a long time and it remains irregular pigmented.
For reduction of reactions the irradiation fields are powdered with indifferent powder. After the erythema development they are greased with cod liver oil or облепиховым oil. At intratissue gamma-therapeutics the skin reactions are expressed more intensively. Dermal papillas lose their integument; the vesicles with serous content appear on irradiated surface. Humid radio dermatitis appears. The area of defeat is quite often covered with the fibrin layer. Epithelization lasts for 2-3 weeks. Then the skin keeps its dark color, it loses its hairy integument. The dressing with boric liquid, prednisolone or methyluracil ointments is used for treatment of exudative radio dermatitis.
The reaction of mucous membranes on irradiation begins with hyperemia and edema, growing with the dose increasing. The mucous membrane loses its brilliancy, seems to be dimmed and densed. Then epithelium desquamation begins and the single erosions, covered with necrotic coating – film, appear. So, the islets of film radioepitheliitis appear. After that follows the phase of confluent film epitheliitis – the erosive surface, covered with white fibrinous coating is defined on bright red background. During 10-15 days after irradiation occurs epithelizaion of erosions, edema and hyperemia of mucous membrane are observed for some time. The radiation reactions of mucous membranes are painful. At irradiation of oral cavity eating is painful, at irradiation of pharynx and esophagus can appear dysphagy, at irradiation of larynx hoarseness is observed. At irradiation of abdomen quite often appears tenesmus, frequent fluid defecation with mucus. The fact is that mucous membrane of small intestines is especially sensitive to ionizing radiation. At the development of radiation cystitis patients complain of painful urination and pollakiuria. With the purpose of prevention and treatment of radiation reactions of mucous membranes the sanation of irradiated cavities is carried out; cancel the irritating components of food are abolished; smoking, alcohol drinks are forbidden. The cavities are irrigated with the weak disinfecting solutions and vitaminized oils (the cod-liver oil, vegetable oil etc.) are introduced into them alternately with 1% solution of novocain.
The radiation reactions inevitably accompany the radiation treatment. But, unfortunately, striving to radical therapeutics in a number of cases can result in local radiation damages. By M. S. Bardychev’s data (1988), their frequency nowadays reaches 10%. As a result of intensive courses of irradiation the radiation damages of different organs and tissues can appear. Subdermal radiation sclerosis, radiation ulcers, pneumonitis, enterocolitis, rectosigmoiditis, radiation dystrophic bone damages, extremely as a result of blood and lymph circulation disturbance and such a severe complication as radiation myelitis are met in medical practice.
The local radiation damages are divided into early and late ones. Damages developed in the process of radiation therapeutics or within 3 months after its completion belong to early ones. Damages, which appear at any period after the expiry of 3 month after radiation therapeutics belong to late radiation damages. The early damages are observed mainly in those cases, when the total radiation dose exceeds the tolerance of irradiated tissues by 30-50% . If the total dose does not exceed the tolerance of tissues or exceeds its slightly, the radiation damages can develop during the remote periods, especially under the unfavorable additional circumstances (the action of mechanical or chemical trauma on irradiation field, insolation etc.). The disturbances of vital activity of skin in these conditions result in arising of radiatioecrosis and then ulcer. The radiation ulcers are characterized by their stability and quite often require the surgical treatment – skin transplantation on the surface of granulations or dissection of injured area with the following plasty. The treatment of local radiation damages must be complex. It consists of generally roborant therapeutics and local application of anti-inflammatory and resorptive medicinal preparations. At the unsuccessful long-term conservative treatment apply the surgical interference. The strict clinic-dissymmetric and radiobiological substantiation and flexible planning of the process of radiation therapy allow avoiding the severe complications in most cases. But, taking into consideration the long period of rehabilitation, the radiation therapeutist together with physicians of corresponding specialties must observe the patients for a long time, realizing the measures, directed on prevention and treatment of possible consequences. The cost of radiation curing of the tumors must not be too high. After the rehabilitation period the patient can be in usual for him living home or working conditions, but he has to follow the doctor’s recommendations and recurrently examination.
6.1. General and local radiation reactions and complications at radiation therapy of maxillofacial malignant tumors.
At radiation therapy of malignancies of maxillofacial area and neck aproximately 10% patients show general radiation reactions of severity degrees, which are mainly characterized by functional disorders and, as a rule, by reversibility of the process.
Such local radiation reactions as erythema, focal (insular) and diffuse (confluent) epithelitis (radiomucositis) appear on the mucosa.
Treatment burn.
All three stages, as a rule, exist at the distance gamma-therapy of mucous cancer of different parts of the mouth. The mucosa of lateral walls of stomatopharynx is the most radiosensitive.
Hyperemia, edema, increased keratinization of mucous membrane grow at continuation of irradiation, the areas of desquamation, erosions covered with whitish film, consisting of fibrin and leukocytes (focal epithelitis) appear.
At the increasing of dose separate erosions pour together. They are covered with whitish-yellow film (diffuse epithelitis).
The development of reaction, even during the first week, is accompanied by perverted taste (absence of perception of sweet, salty, the metallic smack appears), pain at speaking, swallowing, eating. Marked dryness of mucosa (xerostomia) and pain become so intensive that the patients cannot swallow and refuse from the food, persist on the stopping of treatment. Patients are prescribed the anesthetic preparations, antibiotics with nistatin, warm alkaline gargles, cleansing of the oral cavity by hydrogen peroxide, fluid defecation, abundant drinking. The mucosa dryness is especially expressed at irradiation of parotid glands.
The late radiation damages can appear on the part of all tissues, included into the zone of direct radiation influence.
At late periods after cessation of humid dermatitis and diffuse epithelitis the atrophy of skin and mucosa occur. The does not grow hairs on the thin, unbriliat skin its pigmentation is violated (alternation of de- and hyper pigmentation areas).
The mucosa is dry, thin, easy wounded. The tongue without papilla’s becomes varnish.
Radiation dermatitis
The changed areas of skin and mucosa are easily injuring, therefore it is necessary to avoid their mechanical, thermal, chemical trauma, sharp change of temperatures. Necroses with formation of prolonged radiation ulcers, increasing in sizes, uninclined to healing can arise as a result of trauma.
Resume
Radiotherapy uses radiation, usually X-rays, to treat cancer. A beam of radiation is targeted at part of the body where the cancer is. The aim of the treatment is to destroy cancer cells with minimal damage to the surrounding healthy tissue.
Your care may differ from what is described here as it will be designed to meet your individual needs. It’s important that you discuss your radiotherapy with your doctor.
About radiotherapy
Radiotherapy can be used to treat many different types of cancer. About four out of 10 people who have cancer will have radiotherapy as part of their treatment.
Radiotherapy works by destroying the DNA inside cancer cells, preventing them from reproducing and so shrinking cancerous tumours. Healthy cells will also be affected but they are better able to repair themselves.
Radiotherapy can be used for the following reasons.
· To destroy the tumour – this may include radiotherapy on its own or combined with other treatments such as surgery or chemotherapy. If the aim is to cure your cancer with radiotherapy, this is known as primary therapy or radical radiotherapy.
· To reduce the size of a tumour before surgery. This is called neo-adjuvant treatment.
· To make sure all the cancer cells are destroyed after surgery. This is called adjuvant treatment.
· In the emergency treatment of a cancer pressing on your spinal cord to reduce the size of the cancer and prevent damage to your nerves.
· In advanced cancer to slow down the progress of the disease, relieve pain and other symptoms. This is called palliative treatment.
Radiotherapy may be given as one or two treatments, or more often, as a course of treatment usually requiring daily visits on weekdays for between one and six weeks.
Preparing for radiotherapy
Planning a course of radiotherapy can take some time. To find the exact position of the cancer, your doctor will use X-ray pictures and CT scans, to make a three-dimensional image of your body. You may also have MRI scans, which uses magnets and radiowaves to produce images of the inside of your body. Before your treatment starts you will need to come to the radiotherapy department where a special machine called a simulator is used to help plan the exact location and dose of radiation.
The area to be treated has to be positioned accurately each time. To help this, you may have a few tiny dots tattooed on your skin. Occasionally, if the area has to be kept very still, you may need to have a mould made. For example, if your head and neck area is to be treated, you may need to wear a see-through plastic mask or brace to make sure your head remains in exactly the same position for each treatment.
You may have a blood test to see if you have anaemia (low amounts of red blood cells in your blood). If so, you may need to have a blood transfusion to increase the amount of oxygen your blood can carry around your body.
If you smoke, stop – research has shown that giving up smoking may make radiotherapy more effective and reduce possible side-effects of the treatment.
If you have had radiotherapy before to treat a previous cancer, it may be possible to have radiotherapy again to a different area of the body. However, this may differ from person to person so it’s important to discuss your treatment options with your doctor.
What happens during radiotherapy
In most hospitals, a number of different health professionals are involved in providing treatment. This is known as a multidisciplinary team. A clinical oncologist (a doctor who specialises in cancer care using radiotherapy and chemotherapy) will oversee your treatment. The radiotherapy equipment is operated by a therapy radiographer, a healthcare professional trained in using X-rays for treatment. A nurse specialist is often your key contact during treatment and will be available to offer you help and support. You may see other health professionals including a physiotherapist, dietitian and pharmacist. Behind the scenes, medical physicists are responsible for calculating safe and effective doses of radiation.
There are two main types of radiotherapy treatment – external radiotherapy and internal radiotherapy.
External radiotherapy
External radiotherapy is delivered by a machine known as a linear accelerator. It produces high-energy beams of radiation, either as X-rays or gamma rays.
The course of treatment will be planned by a clinical oncologist. He or she will plan your treatment by taking into account the size of your cancer, its likely sensitivity to radiation and the sensitivity of your surrounding tissues. He or she will also take into account your general health and fitness, and will discuss any possible side-effects that you may need to prepare for.
The number and duration of your radiotherapy sessions depends on the type of cancer and where it’s located in your body. A superficial skin cancer may need only a few treatments, whereas a cancer deeper in your body may need longer treatment. It may also depend on whether you’re having treatment to cure the cancer or treatment to reduce your symptoms.
External radiotherapy is given in daily doses called ‘fractions’. For each fraction of radiotherapy you will be asked to sit or lie down in a fixed position. The radiotherapy equipment can be positioned with great accuracy to target the beam of radiation exactly on the right spot. This may involve lying down while the machine rotates around you, or you may be asked to sit in a chair while the beam is directed at a tumour that is near the surface of your skin. The machine won’t actually touch you at any point, but it can be quite noisy, with whirring and buzzing sounds. There is an intercom so you can communicate with the radiographer at all times.
Radiotherapy won’t make you become radioactive during or after the treatment because no radiation-producing material gets inside your body. You will be able to carry on with many of your normal daily activities. However, you may feel tired during and after your treatment so it’s a good idea to ask friends and family for help and support if you need it.
External radiotherapy
Internal radiotherapy
Internal radiotherapy is where the source of radioactivity is put inside your body so it can get closer to the cancer. This can be done in two ways:
Brachytherapy
This is when a solid source of radiation is put next to a tumour to give a high dose of radiotherapy. This means the effect on healthy tissue around the cancer is as little as possible. Brachytherapy can be used to treat cancers of the cervix, womb (uterus), prostate and skin.
For women who have gynaecological cancers, such as cervical cancer, the radiation source is placed inside the vagina during the treatment. This means you may need to stay in hospital for a day or two during treatment.
For other cancers, you may need to have a minor operation under general anaesthesia to put the radioactive source into your body. This may be removed after several hours or even days. Hospital visiting may be restricted at this time because you will be radioactive while the source is in place.
For prostate cancer, small radioactive pellets, known as seeds, are placed into the prostate gland. These deliver a steady dose of radiation to the prostate. This type of source gradually loses its radioactivity and stays in your body permanently. This won’t cause you any harm.
Radioisotope therapy
This is when a radioactive substance, a radioisotope, is used to treat your cancer. It may be given either as an injection into a vein, capsules that you can swallow or as a liquid you can drink. Radioisotope treatment is often used for cancers of the thyroid gland.
After radioisotope therapy, your body will give off small amounts of radiation so you may need to stay in isolation for some time after treatment and then take precautions, such as not getting close to pregnant women or children, for several days afterwards. The radioactive material leaves your body in your sweat and urine. You may be given advice on safety precautions, such as flushing the toilet twice after urinating, to minimise any risk to other people.
Recovering from radiotherapy
After the treatment, your clinical oncologist will arrange a follow-up appointment to check how you’re recovering from any side-effects and what your response has been to the radiotherapy. This is a good opportunity to discuss any concerns or to ask about any long-term side-effects that you might expect to have after your treatment. Patient support groups can give you support and advice on recovering after radiotherapy.
What are the risks?
Side-effects
These are the unwanted, but mostly temporary, effects of a successful treatment. The side-effects may vary depending on what part of your body is treated and the type and dose of your radiotherapy. You will be given information about the side-effects specific to you before you start treatment. Depending on which part of your body is treated, possible side-effects immediately after radiotherapy may include:
· tiredness
· loss of appetite
· feeling sick and vomiting
· diarrhoea
· red, sore or itchy skin
· coughing and shortness of breath
· a dry mouth or sore throat, causing difficulty swallowing
· weight loss
· hair loss – usually temporary but it can be permanent (this only happens in the area of the body being treated)
· emotional symptoms – feeling low, depressed or anxious after treatment
· stiffness of joints and muscles
Radiotherapy can also cause some long-term side-effects such as:
· darkening of your skin
· your hair may grow back a different texture and colour
· hair loss that is sometimes permanent
· tiny red marks on your skin from broken blood vessels
· swelling of your arms and legs, due to the blockage of lymph vessels (this is called lymphoedema)
· shortness of breath – if you have had radiotherapy to your chest
· difficulty swallowing due to narrowing of your gullet (oesophagus)
· infertility – if your ovaries or testicles are within the treatment area
Some, but not all people who have radiotherapy to the pelvic region may have side-effects related to their bowel, bladder or sexual function. Your doctor and specialist nurse will be able to offer you advice and support.
Very rarely, radiotherapy can cause a second cancer that may develop several years after treatment. The benefits of the radiotherapy outweigh this risk but it may be something that your doctor will mention to you and is also one of the reasons patients are followed up after treatment.
