The potential benefit from a perfect radiosensitizer and its dependence on reoxygenation

Abstract

The potential benefit of a perfect radiosensitizer was assessed by computing the sensitization ratios that would be observed in a mixed population of oxic and hypoxic cells if different reoxygenation rates existed. The sensitizer was assumed to be as effective as oxygen, completely non-toxic and freely diffusible to all hypoxic cells within the tumor. The calculations were made for several different clinical fractionation regimes, namely 30, 20, 9 or 6 fractions all with the same ret dose (NSD [nominal standard dose] = 1700 rets). The sensitization for differing rates of reoxygenation and for the different fractionation schemes was calculated. The size of the extrapolation number is seen to be an important parameter in these calculations. How much reoxygenation would be needed to abolish the benefit from (and hence the need for) a perfect radiosensitizer was indicated.