The relative biological effectiveness of fractionated doses of fast neutrons (42 MeVd----Be) for normal tissues. III. Effects on lung function.

The effect of single and fractionated doses of fast neutrons (42 MeVd----Be) on the early and late radiation responses of the pig lung have been assessed by the measurement of changes in lung function using a 133Xe washout technique. The results obtained for irradiation schedules with fast neutrons have been compared with those after photon irradiation. There was no statistically significant difference between the values for the relative biological effectiveness (RBE) for the early and late radiation response of the lung. The RBE of the neutron beam increased with decreasing size of dose/fraction with an upper limit value of 4.39 +/- 0.94 for infinitely small X-ray doses per fraction.