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 B6C3F1 mice were compared. Six-week-old animals were divided into 6 groups and exposed to 0.426 Gy heavy ion irradiation of 290 MeV/u carbon-ion beam (LET 60-210 KeV/micron) 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 incidences in the males were 30, 56 and 13% respectively in the heavy ion, 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 than for 0.5 Gy and 5 Gy X-ray irradiation (P < 0.05), the respective incidences, mainly ovary one, being 73%, 17% and 41%. Non-cancerous lesions, 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-irradiation and higher carcinogenicity than that of 0.5 Gy X-irradiation in male mice.