Response of mouse intestine to 14 MeV neutrons.

At the Hamburg-Eppendorf Hospital neutron facilities the relative biological effectiveness (r.b.e.) of d,T-neutrons was determined with respect to survival of mouse intestinal crypts. (CBA/Rij x C57BL/Rij)F1 mice were irradiated to the whole body at different depths inside a tissue-equivalent phantom. Irradiations were carried out with a collimated neutron beam at about 6 rad/min given in single doses ranging from 450 to 1000 rad. For reference, gamma-rays from a 60Co therapy unit were used. The number of surviving intestinal crypts per circumference of the jejunum was determined 3 1/2 days after irradiation according to the method of Withers and Elkind. The number of surviving stem cells was calculated on the basis of Poisson statistics. The doses necessary to reduce survival to ten crypt stem cells per circumference amounted to 689 +/- 19 rad for neutrons and 1449 +/- 29 rad for 60Co gamma-rays. From these figures an r.b.e. of 2 . 1 +/- 0 . 1 is obtained. Measurements at different depths in the phantom did not show any variation of r.b.e. with depth along the axis of the neutron beam.