Oncogenic Transformation of C3H/10T½ Cells by X-rays, Fast-fission Neutrons, and Cyclotron-produced Neutrons

Lethality and oncogenic transformation were measured in C3H/10T1/2 murine fibroblasts exposed to neutrons and X-rays at doses between 0.5 and 11 Gy. Transformation results with X-rays and low-energy, reactor-produced neutrons were used as a baseline to compare and evaluate the results obtained with high-energy, cyclotron-produced neutrons. The radiations were 100-kVp X-rays at 0.49 Gy min-1, reactor fission neutrons at 0.10 to 0.31 Gy min-1 with an 8 to 20 per cent gamma dose component, and cyclotron-produced neutrons at 0.51 Gy min-1 with mean energy 38 MeV and an 8 per cent gamma dose component. The radiobiological effectiveness (r.b.e.) for cell lethality was 2.4 +/- 0.2 for fission neutrons and 1.7 +/- 0.1 for high-energy neutrons. The maximum proportions of transformants per thousand surviving cells were, respectively, 3.7 +/- 0.8, 6.5 +/- 0.7, and 2.3 +/- 0.6 for X-rays, fission neutrons, and cyclotron-produced neutrons. The maximum observed r.b.e. for transformation induction was 3.8 for fission neutrons and 1.2 for cyclotron neutrons. Thus, high-energy neutrons exhibit a higher r.b.e. for cell killing capacity than for oncogenic transformation in C3H/10T1/2 cells.