Response of mouse intestine after single and fractionated irradiation with accelerated carbon ions with a spread-out Bragg peak.

The responses of mouse intestine were examined after irradiation with accelerated carbon ions with a spread-out Bragg peak. The carbon-ion beam (135 MeV/nucleon), accelerated by the RIKEN ring cyclotron facility, was modulated to have a spread-out Bragg peak (SOBP) 3 cm wide. In the SOBP the biological dose (relative physical dose x RBE) was designed in earlier studies to be flat at the 10% survival level of Chinese hamster V79 cells. The numbers of surviving crypt clonogenic cells after single and fractionated irradiation with the carbon-ion beam were obtained by a microcolony assay method. The composite single-dose survival curves for the crypt clonogenic cells were calculated and fitted by a linear-quadratic (LQ) model. An analysis with the LQ model for crypt clonogenic cells showed that the alpha coefficient increased along with increasing LET, and that the beta coefficient was relatively constant, even for high-LET radiations. The biological dose distributions for the crypt clonogenic cells at the 10% survival level were flat in the SOBP. The isoeffective design of the SOBP for the 135 MeV/nucleon carbonion beam, based on biological data from a mammalian in vitro cell system, appears to be applicable to the response of murine intestinal tissue in vivo.