COMPARISON OF TUMORIGENESIS BETWEEN ACCELERATED HEAVY-ION AND X-RAY IN B6C3F1 MICE

The effects of heavy ion and X-ray irradiation on tumorigenesis in B6C 3F1 mice were compared. Six-week-old animals were divided into 6 group s and exposed to 0.426 Gy heavy ion irradiation of 290 MeV/u carbon-io n beam (LET 60-210 KeV/mu m) at the dose rate of 0.4 +/- 0.2 Gy/min; 0 .5 Gy of X-ray irradiation at 0.1 Gy/min or 5 Gy of X-ray irradiation at 1 Gy/min. The mice were killed and an autopsy performed 13.5 months after the whole body irradiation. Body weights were heaviest for both sexes in the 0.5 Gy group and Lightest in the 5 Gy one. Total tumor i ncidences in the males were 30, 56 and 13% respectively in the heavy i on, 5 Gy and 0.5 Gy X-irradiated groups, stomach tumors, lymphomas and adrenal tumors being the most common outcome of the high dose X-rays. Liver tumor induction did not differ significantly among the groups. In the females tumorigenicity was significantly lower for heavy ion th an for 0.5 Gy and 5 Gy X-ray irradiation (P < 0.05), the respective in cidences, mainly ovary one, being 73%, 17% and 41%. Non-cancerous lesi ons, such as graying of the hair, glomerular sclerosis and amyloidosis appeared in the 5 Gy group. These findings indicate that 0.426 Gy of heavy ion irradiation induced lower carcinogenicity than 5 Gy of X-irr adiation and higher carcinogenicity than that of 0.5 Gy X-irradiation in male mice.