Response of Chinese hamster ovary cells to fast neutron radiotherapy beams. I. Relative biological effectiveness and oxygen enhancement ratio

The relative biological effectiveness (RBE) and oxygen enhancement ratio (OER) were determined for fast neutron beams produced by both 16-MeV and 50-MeV 2H on Be at the Texas A and M Variable Energy Cyclotron (TAMVEC). These beams have average neutron energies of 7 and 21 MeV, respectively. The biological system used in these experiments was Chinese hamster ovary cells in tissue culture. The results indicated that although the RBE of the 21-MeV beam was about 15 percent lower than that for the 7-MeV beam at 0.1 percent survival there was no change in RBE for either beam with depth in a tissue-equivalent phantom. The OER of the 7-MeV beam was found to be 1.5 +- 0.3 and the 21-MeV beam had an OER of 1.2 +- 0.2, which resulted in gain factors of 1.7 and 2.1, respectively, when compared to 60Co gamma rays (OER = 2.5). No variation in OER with depth was detected. It was concluded that the 21-MeV TAMVEC beam should be as applicable to radiotherapy from the radiobiological point of view as a 7-MeV beam