Cyclotron fast neutron RBE for various normal tissues.

The relative biological effectiveness (RBE) values of fast neutrons as a function of dose in the range of dose per fraction being used clinically are reported for effects on several normal mouse tissues. The specific tissues examined were: thymus, spleen, white blood cells (WBC), testes, and small intestine. The RBE values for damage to the thymus (1.2), spleen (1.2), WBC (1.0), and testes (3.0) were independent of neutron dose size. In contrast, the RBE for the small intestine varied between 2.7 and 3.4 and was dependent on the size of the neutron dose. The RBE for intestinal death (2.4) and hematopoietic death (1.1) also is reported.