Abstract
The effect of 30-MeV D+ .fwdarw. Be NIRS [National Institute of Radiological Sciences, USA] cyclotron neutrons on a spontaneous [mouse] 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 [relative biological effectiveness] of 200-kVp X-rays at the 10% survival level was 1.9 for aerobic cells and 2.0 for hypoxic cells; the OER [oxygen enhancement ratio] at the same level was .simeq. 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+ .fwdarw. Be neutrons was inversely related to deuteron energy for hypoxic cells. The relationship between TGD and peak skin reaction indicated no benefit from mixed beams or 5 neutron doses.

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