Comparison of the effects of neutron and/or photon irradiation on spontaneous squamous-cell carcinoma in mice.

The effect of 30MeV D+ leads to Be NIRS cyclotron neutrons on a spontaneous NR-S1 squamous-cell carcinoma was studied. The TD50 (number of tumor cells required for transplantation in half the sites) and tumor growth delay time (TGD) were determined. The RBE of 200-kVp x rays at the 10% survival level was 1.9 for aerobic cells and 2.0 for hypoxic cells; the OER at the same level was congruent to 1.7. Tumor cells irradiated with neutrons were unable to repair potentially lethal damage, in contrast to x-irradiated tumor cells. The RBE of 50-MeV D+ leads to Be neutrons was inversely related to deuteron energy for hypoxic cells. The relationship between TGD and peak skin indicated no benefit from mixed beams or 5 neutron doses.