Relative Biological Effectiveness of Cyclotron Fast Neutrons for Late Hepatic Injury in Rats

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Abstract
Surgically exteriorized left anterior liver lobes were exposed to single graded doses of fast neutrons (0-2250 rad) or .gamma. rays (0-9000 rad). A dose-dependent decrease in liver function, as measured by 131I-rosebengal uptake in the exposed liver, was observed 1 yr after exposure. Fibrosis in the liver, as measured by hydroxyproline levels, increased 1 yr after irradiation and was dose-dependent. Using these 2 endpoints, a neutron RBE [relative biological effectiveness] of 4-6 at a neutron dose of 950 rad was estimated and corroborated by histological examination of the irradiated liver. Of 96 animals, 13 developed neoplasms within 1 yr after exposure. Of the neoplasms, 11 occurred in the neutron-irradiated animals. The tumors were squamous cell carcinoma (5 animals) or mammary adenocarcinoma (8 animals). [Hepatic injury is of concern during radiotherapy of human tumors of the upper abdomen and lower thorax].