Radioresistance of mouse intestine induced by carbon-ion irradiation

The purpose of this paper is to report that gut crypt cells become radioresistant after single or fractionated irradiation with intermediate LET carbon ions. C3H female mice received whole body irradiation with 20 keV/mm carbon ions, and served the jejunum for crypt survival assay 3.5 days after irradiation. Dose-crypt survival relationship showed that the D0 value increased from 1.06 Gy to 1.94 Gy when the first dose of 9.0 Gy was followed by single graded doses of carbon ions with an interval time of 4 hr. The Increased D0 gradually decreased with a half decay time of 50 hr, and returned to 1.08 Gy, a similar value of single irradiation. When mice received 1 Gy carbon ions for 9 fractions with an interval time of 4 hr each, the D0 value of crypt cells surviving the preceding total dose of 9 Gy also increased to 1.89 Gy. The D0 increase was less prominent when the size of first or preceding dose was small. It is concluded that charged particles with intermediate LET produce a unique biological response, and would be beneficial for radiotherapy of visceral tumors