ROLE OF RADIOADAPTATION ON RADIATION-INDUCED THYMIC LYMPHOMA IN MICE

Thymic lymphoma (TL) was observed in different stages of development i n 46% of male mice (23/50) following exposure to an acute challenge do se of 2 Gy Co-60 gamma-rays. With an adapting dose of 1 cGy 24 h prior to the challenge dose of 2 Gy, similar growth of TL was seen in 42.5% of mice (17/40). TL was not found in unirradiated control mice (0/50) or in the group treated with 1 cGy (0/50). Multiple adapting doses fo r 5 or 10 consecutive days induced TL in 8/50 and 9/50 mice, respectiv ely (17% in average). When multiple adapting doses were followed by th e challenge dose, the yield of TL was much lower, 16% (8/50) and 30% ( 15/50), respectively. By 15, 30, 60, 90, and 120 days after exposure w ith 3 Gy of Co-60 gamma-rays, TL developed in 30, 70, 70, 80 and 85% o f the female mice, respectively. When mice were conditioned with an ad apting dose of 1 cGy 24 h prior to the challenge dose, TL was not foun d 15 days post-irradiation, while about a 25% reduction in the occurre nce of TL was noticed at all other intervals. The results suggested th at an adapting dose could play a role in bringing about a change in te rms of delay and inhibition of the acute effects of radiation, i.e., t he onset of TL in mice.