Response of mouse intestine after fractionated doses of accelerated carbon-ion with spread-out bragg peak

For the clinical trial of heavy ion radiation therapy, it is necessary to know the effects of the fractionated dose of accelerated heavy ions on various biological systems. The response of mouse intestines to the fractionated dose of carbon beam was examined. The carbon beam of 135 MeV/u accelerated with the RIKEN ring cyclotron was modulated to have a spread-out Bragg peak of 3 cm width. The flatness of biological effect for the spread-out Bragg peak was investigated. C3H female mice of 16 - 22 weeks age were used. The mice were subjected to the whole body irradiation with unmodulated carbon beam at different depth in spread-out Bragg peak (SOBP). The SOBP was designed for 135 MeV/u carbon beam so that V79 cells were uniformly killed in the peak. The responses to the γ-ray of a 137Cs unit for the reference and the neutron beam of the NIRS cyclotron were also used. The equal dose of three fractionated exposures was given at 4 h intervals. The number of surviving ileum crypt cells was examined three and a half days after the irradiation. The effects of anesthesia in the γ-ray and neutron irradiations, the surviving crypt stem cells and the biological dose for SOBP are reported. (K.I.)