Heavy ion beam model for radiobiology

Abstract

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.

Some Comments on the Concepts of Dose and Dose Equivalent

“…For cellular survival, track structure theory has been shown to represent an adequate model for cell killing by high-LET radiations of demonstrated predictive value (Katz and Sharma, 1973;Roth and Katz, 1980). Although mechanisms leading to other biological end points may be more complex, experimental data suggest that the general pattern of radiation response is similar to that for cellular inactivation.…”

“…These spectra are presently only available for neutrons (Caswell and Coyne 1972) and are presently being studied for heavy ion beams (Schimmerling et al 1983). Where the particle-energy spectra and the low-LET contamination are known, the equations of Table 1 make it possible to calculate cellular survival from cellular radiosensitivity parameters (Katz and Sharma, 1973;Katz and Sharma 1974;Roth and Katz, 1980).…”