A comparative study of dose distribution of a high-energy electron beam and chromosome aberration frequencies

Electron beam therapy is usually employed for the treatment of tumours located at or near the surface of the body, because the electron beam gives a high dose near the surface, but falls off rapidly with increasing depth beyond the level of the 80% depth dose. Isodose curves for radiotherapy have been obtained using physical methods, but have rarely been investigated on the basis of living human cells. In the present study, lymphocyte chromosome analysis was employed as a biological dosemeter for comparison with the isodose curve measured physically. The peripheral blood was exposed to a 14 MeV electron beam in a plastic tube set in a specially made test-tube stand immersed in a water tank. The chromosome aberration frequencies induced by irradiation of about 95% of peak dose at a depth of 31 mm were found to be higher in value than those induced at a depth of 17 mm where the peak dose had been determined physically. Three gray of irradiation given to whole blood in the presence of contrast medium gave rise to a slight enhancement of radiation-induced chromosome aberration frequencies in the lymphocytes exposed at a depth of 17 mm, but a slight decrease at 31 mm.