High-energy radiation as the chief weapon of the radiotherapeutist in malignant tumour therapy

A comparison is made of the sources of high energy radiation used in the radiotherapeutist malignant tumour. The orthovoltage X-ray therapy uses X radiation of a voltage of up to 250 kV. Such radiation very quickly decreases from its maximum at the surface of the irradiated field to the deep tissue layers owing to absorption and drops to 50% of the skin dose at the depth of 7 cm. The skin dose in X-ray therapy fractioned to 25-30 irradiation days should not exceed approximatety 3000 R. The use of the high energy electromagnetic radiation results in the manifestation of the buildup effect and the dose maximum is shifted more to the surface of the body the higher is its energy. The energy of the 137Cs gamma source is 660 keV and the dose decrease in the body is rather steep. The isodose curves show that the maximal dose is recorded in the depths of 1.5-3 mm, that the dose decreases towards the surface and that on the skin there remains but 80% of the maximal dose. For the gamma radiation of the 60Co source (having an energy of 1.25 MeV) the dose maximum is in the depth of 5 mm under the surface and of this dose only about 50% remains on the surface of the 100 cm2 area of the entrance field. X-ray therapy is today used mainly for the treatment of surface and subsurface diseases, for carcinomas in the vicinity of the body axis in those cases when a carcinolethal dose is not necessitated. The high-energy radiation of 137Cs and 60Co gamma sources has significantly lower skin and total reactions and simplifies and specifies irradiation techniques and planning. Cesium therapy is applied to tumours sited at medium depth and 60Co has become the main radiation source in the treatment of depth tumours. (B.S.)