Heavy ion beam model for radiobiology.

An ad hoc model of energetic heavy ion beams, including secondary and tertiary particles, has been constructed for predicting radiobiological experiments. While the beam model is relatively primitive, it yields depth-dose and depth-radiobiological calculations in good agreement with experiment upstream of the Bragg peak. Beyond the peak, the model is somewhat coarse grained and seems to underestimate low-LET fragment production. These defects can be repaired at some cost in computer time. Presently a complete set of depth-dose and radiobiological results (RBE, OER, aerobic and hypoxic survival) is obtained in 4–8 min, for a single beam, at a cost of $10. The model can be extended to mixed radiation fields, or to explore the design of ridge filters. These predictions are based on cellular radiosensitivity parameters extracted from track-segment irradiations at about 8 MeV/amu. Their success implies that no new radiobiological results arise from irradiation with beams at 500 MeV/amu.