GAMMA THERAPY (scale [-radiation] + grech, therapeia treatment) — the type of radiation therapy based on use of gamma radiation.
Natural isotopes — radium and mesothorium and artificial — cobalt, caesium, iridium and tantalum are sources of gamma radiation.
Long half-life of these isotopes ( 226 Ra — 1620, 228 Msth — 6,7 years, 60 With — 5,25 years, 137 Cs — 30 years, 192 Ir — 74,4 days, 182 They are 111 days) causes their use only for outside radiation; into fabrics they are entered in the bottletight metal tubes filters made or from heavy metal (for 226 Ra and 228 Msth), or from nickel, stainless steel or a thin coat of gold (for 60 With, 137 Cs, 192 Ir, 182 That).
G.'s technique - t. (an arrangement of a source of radiation in relation to the irradiated body) depends on localization, volume and gistol, structures patol, educations.
Remote gamma therapy
Remote gamma therapy (telegamma therapy) is applied in a combination with a surgical method of treatment — before operation — and independently to treatment according to the radical plan or with the palliative purpose. Under the influence of preirradiation change biol, properties of a tumor, mitotic activity of tumor cells decreases, anaplastic cells, the most inclined to dissimination therefore the frequency of a recurrence and metastasises decreases collapse. The purpose of postoperative radiation — impact on the cells disseminated during operation, and at not radical operations and on residual tumoral fabric. As an independent method of treatment remote G. - t. apply for the purpose of achievement of full regression of a tumor by destruction of the tumor cells, permanent disturbance of processes of reproduction of less sensory cells, most sensitive to radiation, and strengthening of reaction of surrounding connecting fabric, edge, expanding in the tumor and around it, divides a tumor into separate complexes and breaks its blood supply.
Source of radiation ( 137 Cs, 60 With) is at distance of 6 — 75 cm from a body surface of the patient. For treatment patol, the processes located at a depth of 3 — 5 cm from a body surface (throat cancer, almonds, a thyroid gland, metastasises of cancer in peripheral limf, nodes), it is possible to make radiation as on small, and at a great distance; at localization patol, process at a depth more than 5 cm — only at a great distance. Radiation can be static and mobile. In the first case a source of radiation and the patient are in the fixed situation. At mobile radiation the source of radiation moves concerning an axis of a body of the patient (long or short) usually on 90 — 360 °. The angle of rotation from 360 to 240 ° is shown at the central arrangement of a tumor, the longitudinal axis a cut matches or is parallel to an axis of a body of the patient. At an eccentric arrangement of a tumor the angle of rotation shall be less. Eccentric sector radiation is applied at a superficial arrangement patol, educations. Mobile radiation allows to concentrate a maximum of a dose in the area patol, the center and to reduce it by body surfaces. Rotation of a source of radiation can be made around one, two or four axes. Two - and eight-wheel radiation are applied at treatment extended patol, processes in bodies of a basin more often. The sizes of fields of radiation define so that primary tumor and regional metastasises entered a zone of 100% of an isodose, and in a zone of 80% of an isodose — area subclinical spread of a tumor. In process of reduction of the sizes of a tumor in the course of G. - t. fields of radiation, considering small tolerance of the healthy bodies and fabrics included in the radiation zone, and big radio sensitivity of a peripheral part of a tumor (see. Radiochuvstvitelnost ), respectively reduce. For movement of a maximum of a dose in patol, the center for protection of radio sensitive bodies against a radiation effect is applied by lead blocks and wedge-shaped filters. At G. - t. big tumors for increase in tolerance of hypodermic cellulose and close located bodies and fabrics it is necessary to use lead lattices or rasters. The size of the general focal dose at remote G. - t. is defined gistol. structure of a tumor or character patol, process, its distribution, localization, age of the patient, existence of associated diseases. Radiation is made fractionally. Doses and intervals between radiations depend on duration of a mitotic cycle of tumor and normal cells and on other factors. At daily fractional irradiation the single dose makes 150 — 250 is glad; at radiation with 2 — 3-day intervals — 300 — 500 I am glad; at large fractional irradiation at an interval of 7 days — 700 — 1000 I am glad. At increase in a single dose respectively reduce the general dose.
The choice of conditions of radiation (distance «a source — a tumor», the sizes and localization of fields of radiation) is based on detailed studying of topography of a tumor by means of a X-ray analysis, a tomography, a limfografiya (for the purpose of identification of a state limf, nodes), scannings and endoscopies. According to data of these researches for each patient on cards prepare the cross and sagittal cuts passing through the center of a tumor on which draw curves isodoses (see) under the chosen conditions of radiation. During the performing treatment consider the dose absorbed by a tumor and the nearest important bodies, an air dose on skin of each field and an integral dose. During the calculation of doses it is necessary to consider distinction of fabrics on density.
At cancer therapy of band bodies (a neck and a body of the womb, a rectum, a bladder, a nasopharynx, a gullet, etc.) remote G. - t. it is reasonable to combine about intracavitary.
Intracavitary gamma therapy
Intracavitary gamma therapy apply at small tumors of a rectum, bladder, a nasal cavity after removal of small exophytic tumors of these bodies or at any sizes of a tumor in combination with outside radiation (at cancer of a vagina, uterus, rectum, bladder, gullet, nasopharynx). Intracavitary G.'s use - t. it is caused by need of increase in a focal dose for the most resistant part of a tumor that is quite possible owing to bystry power loss of a dose of radiation at its distribution in fabrics (already at a depth of 2 cm there are about 40% of a dose). As a source of radiation use drugs 60Co of cylindrical or spherical shape (a so-called beads) covered with inactive gold.
Enter into the affected cavity and fix in it special applicators, probes or cylinders. Situation them in relation to a tumor and the next bodies is controlled according to roentgenograms. Radioactive drugs from a container or automatically move in the manual way to applicators. Dosage rate is defined depending on character and distribution patol, process. Radiation with high dosage rate is carried out within 30 — 60 min. at an interval of 1 week (at cancer of a neck, a body of the womb and a rectum), with a low power — during 4 — 8 hours at an interval of 3 — 4 days (at cancer of a gullet, nasopharynx and rectum) or during 24 — 48 hours at an interval of 5 — 6 days (at cancer of a neck, a body of the womb and a nasopharynx). Depending on localization patol, the center and type of fractionation of application repeat 2 — 6 times.
Interstitial gamma therapy
Interstitial gamma therapy apply at treatment of accurately delimited tumors with a diameter no more than 5 cm, with average and small radio sensitivity (cancer of language, a mucous membrane of an oral cavity, an under lip, skin, a recurrence of tumors various gistol, structures, inoperable metastasises in limf, nodes, cancer of a bladder in the first stage, cancer in the field of the proctal channel). At interstitial G. - t. radioactive drugs in the form of needles or naylonovy tubules containing b0so, 182 That or 192Ir (see. Radioactive drugs ), enter directly into a tumor and around it, having their parallel ranks at distance 1 — 1,5 cm from each other or on a rectangle. For fixing of radioactive needles use devices from plexiglas or plastic. In addition to the gamma radiating drugs, it is possible to apply liquid isotopes with the mixed radiation (scale and a beta). At administration of drugs it is necessary to follow rules of an asepsis.
Radiation is made with a low power of radiation continuously within 6 — 8 days. The general dose depending on the volume irradiated patol the center — 5000 — 7000 I am glad at the power of radiation of 30 — 40 is glad in an hour. Distribution of a dose at interstitial radiation is characterized by bystry falling of its power at distance of 1 cm from drug thanks to what the local influence providing its high biol, efficiency is carried out.
At metastasises of cancer of oral cavity and throat in limf, nodes of submaxillary area and a neck, at a breast cancer, sarcoma of soft tissues and others the resectable and standing on a side of not operability malignant tumors, and also for the purpose of prevention of a recurrence and metastasises of a tumor on a peritoneum and limf, to ways after operation for a carcinoma of the stomach, intestines and ovaries apply a radio surgical method of interstitial G. - t.: the tumor is deleted, and in its bed and in surrounding fabrics administer the radioactive drugs or fabrics infiltrirut colloidal radioactive solutions. Colloidal solution 198Au, divorced in isotonic solution of sodium chloride, is entered into an abdominal cavity in 10 — 14 days after operation. Apply 0,25% to anesthesia of a peritoneum solution of novocaine: 200 ml before administration of radioactive drug and as much later.
Application gamma therapy
Application gamma therapy it is shown at high-quality (cavernous angiomas) and the malignant tumors of skin and mucous membranes extending on a surface and infiltriruyushchy fabrics deep into no more than to 1 — 1,5 cm. Sources of radiation (60so, 137Cs) have in one plane in the form of a rectangle, a square or a polygon. Drugs stack on previously prepared mold (model) of the struck area made of the plastic, hardening at the room temperature weight. In process of passing of radiation through tumoral fabric bystry power loss of a dose is noted: at a depth of 2 cm normal fabrics are not damaged. Radiation is carried out daily fractionally, a single dose — 200 — 600 I am glad during 4 — 10 hours a day. Due to the difficulties of radiation protection of sick and service personnel the application method is applied seldom.
Complications at G. - t., as well as at other types of radiation therapy (see. Beam damages ), arise at the decrease in tolerance of normal fabrics and bodies caused by associated diseases (a hypertension, hypotension, diabetes, allergies of various etiology, cardiovascular insufficiency, avitaminosis, proteinaceous starvation, obesity). Also mistakes can be the cause of complications during the scheduling of therapy and lack of the accounting of radio sensitivity of the next bodies; in rare instances — high individual radio sensitivity.
Character of complications is defined also by method G. - t. At remote G. - t. complications are more often shown by development of a sclerosis and atrophy of the irradiated fabrics and bodies (fibrosis of hypodermic cellulose, a pneumosclerosis, etc.); the most serious complications of intracavitary G. - t. — perforation of body, beam ulcers, fistulas; at interstitial G. - t. (in case of an arrangement of radioactive drugs it is close to a cartilaginous or bone tissue) — beam perichondrites, osteomyelitis and beam ulcers (in soft tissues).
Contraindications to G. - t.: 1) absolute — a cachexia, exhaustion, dekompensirovanny forms of heart diseases, a liver, kidneys, a hypoplasia of marrow, existence of fistulas in the next band bodies and the expressed sclerous changes in fabrics caused by the previous radiation therapy, the progressing forms of tuberculosis; 2) relative — the inflammatory processes accompanying development of a tumor, extensive tumoral processes, tendency of a tumor to disintegration and bleeding.
Bibliography: Kozlova A. V. Radiation therapy of malignant tumors, M., 1971, bibliogr.; P and in l about in A. S. Interstitial gamma and beta therapy of malignant tumors, M., 1967, bibliogr.; Ratner T. G. and Bieber g and l A. V. Formation of dozny fields at remote gamma therapy, M., 1972, bibliogr.
A. V. Kozlova.