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

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Abstract
Chinese hamster lung (V-79) and human kidney (T-1) 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 Pb (translational) ridge filter and a brass (spiral) ridge filter designed to produce extended peaks of .apprx. 4 and 10 cm, respectively. Stationary-phase and G1-phase populations of Chinese hamster cells had different absolute radiosensitivities which, in turn, were different from that of asynchronous human kidney cells. The increase in relative biological effectiveness (RBE) observed carbon ions were slowed down and stopped in water was similar for the 3 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 .apprx. 2.0 and 1.7 for the 4 and 10 cm extended peaks, respectively. O2 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 varied between values of 2.4 to 1.55 from the proximal to distal positions.

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