RESPONSE OF MOUSE INTESTINE AFTER SINGLE AND FRACTIONATED-IRRADIATIONWITH 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 b eam (135 MeV/nucleon), accelerated by the RIKEN ring cyclotron facilit y, was modulated to have a spread-out Bragg peak (SOBP)3 cm wide. In t he SOBP the biological dose (relative physical dose x RBE) was designe d in earlier studies to be flat at the 10% survival level of Chinese h amster V79 cells. The numbers of surviving crypt clonogenic cells afte r single and fractionated irradiation with the carbon-ion beam were ob tained by a microcolony assay method. The composite single-dose surviv al curves for the crypt clonogenic cells were calculated and fitted by a linear-quadratic (LQ) model. An analysis with the LQ model for cryp t clonogenic cells showed that the alpha coefficient increased along w ith increasing LET, and that the beta coefficient was relatively const ant, even for high-LET radiations. The biological dose distributions f or the crypt clonogenic cells at the 10% survival level were flat in t he SOBP. The isoeffective design of the SOBP for the 135 MeV/nucleon c arbon-ion beam, based on biological data from a mammalian in vitro cel l system, appears to be applicable to the response of murine intestina l tissue in vivo. (C) 1997 by Radiation Raearch Society.