Radiation Biophysical Studies with Mammalian Cells and a Modulated Carbon Ion Beam

Abstract

CHAPMAN, J. D., BLAKELY, E. A., SMITH, K. C., URTASUN, R. C., LYMAN, J. T., AND TOBIAS, C. A. Radiation Biophysical Studies with Mammalian Cells and a Modulated Carbon Ion Beam. Radiat. Res. 74, 101-111 (1978). Chinese hamster (V-79) and human kidney (T-l) cells were irradiated in stirred suspensions placed at various positions in the plateau and extended Bragg peak of a 400-MeV/amu carbon ion beam. The range of the ions was modulated by a lead (translational) ridge filter and a brass (spiral) ridge filter designed to produce extended peaks of -4 and 10 cm, respectively. Stationary-phase and Gi-phase populations of Chinese hamster cells were found to have different absolute radiosensitivities which, in turn, were different from that of asynchronous human kidney cells. The increase in relative biological effectiveness (RBE) observed as carbon ions were slowed down and stopped in water was similar for the three cell populations at doses greater than 400 rad. At lower doses the RBE was greater for the hamster cell populations than for the human kidney cells. The gain in RBE (at the 50% survival level) between the plateaus and the middle region of the extended peaks was -2.0 and 1.7 for the 4- and 10-cm extended peaks, respectively. Oxygen enhancement ratios (OER) were determined at the 10% survival levels with stationary-phase populations of hamster cells. Values of 2.8, 2.65, and 1.65 were obtained for the OER of 220-kV X rays, plateau carbon, and the middle region of the 4-cm carbon peak, respectively. Across the 10-cm carbon peak the OER was found to vary between values of 2.4 to 1.55 from the proximal to distal positions.