INDIRECT EFFECTS OF RADIATION ON THE TUMOR GROWTH

1. Pretransplantation irradiation with a dose of 500R delivered locally to the right thigh before the intra-muscular inoculation of a tumor cell supension delayed the growth of Yoshida sarcoma in Wistar strain rat.The degree of delay of the tumor growth measured on the sixth day and ninth day after inoculation were 38 % and 50 % of the tumor weight in the unirradiated control group, respectively.The mechanism of this action might be considered that an increase in capillary permeability and exsudation of inflammatory cells in the irradiated normal tissue inhibit the lodging of the transplanted tumor cells.2. The growth inhibition of the tumor irradiated with 500R immediatly after inoculation were higher than summation of the tumor bed effect and direct cytocidal effect.This mechanism might be due to a disturbance of the repair of sublethal damage and/or potentially lethal damage in the irradiated tumor cells.