Daily D-T Neutron Irradiation of Mouse Intestine

The intestinal microcolony assay technique, for measuring damage to the progenitor cell population of mouse jejunal epithelium, has been used to demonstrate the following: Single doses of collimated 14-MeV D-T neutrons (10 to 30 rad min$sup -1$) are more effective than single doses of 300-kV x-rays or Cs- 137 $gamma$-rays (30 to 650 rad min$sup -1$) by a factor of 1.9 to 2.3 for a reduction in crypt numbers of 50 to 80 percent. For mice irradiated at 10 cm deep in a 30-cm-deep water phantom, the above RBE values are reduced by about 9 percent. The same reduction is applicable for single doses and for four daily dose fractions. With daily fractionated irradiations (up to 5), the iso-effect curves (for 50 percent or 80 percent crypt number depopulation) are linear on a log/log plot, with slope exponents of 0.57 to 0.58 ($gamma$-rays) and 0.32 to 0.34 (neutrons). Estimates of the RBE values for extended fractionated dose regimens are 3.3 (10 daily fractions) and 3.6 (15 daily fractions). (auth)