Response of the R3327-AT1 Dunning prostate tumor to fast neutrons and cobalt-60.

Reasons why neutron therapy may be successful include tumor's rate of proliferation, state of oxygenation at time of onset of radiation and the efficacy of reoxygenation during therapy, inherent radioresistance and repair capacity. In an effort to better understand the action of neutrons on tumor tissues we started studies with the Dunning rat prostate tumor system. This tumor system has sublines available with differing histologies, doubling times, hormone dependency and metastatic potential. The present report pertains to anaplastic carcinoma R3327-AT1 subline. The tumors transplanted into the distal thigh received single doses of 8 through 15 Gy of 14.5 MeV neutrons and 18 through 30 Gy Co-60 after they had reached a volume of about 450 mm3. The tumors exhibited a dose dependent retardation in further growth. An RBE of 3 was estimated by comparing the time required for a tumor to reach a normalized value of five times the initial treatment volume. We plan to extend our studies to include a slower growing well differentiated subline.