The effects of single and fractionated doses of X-rays and neutrons on the oesophagus

Abstract

Damage to the oesophagus of mice after irradiation with single doses, 2, 5 or 10 equal fractions of X-rays or fast neutrons was measured by estimating ld 50 values for death between 10 and 40 days post-irradiation of the thorax. The slope of the isoeffect curve for X-irradiation was 0.40 and for neutrons was 0.29. RBE values obtained for oesophaged damage are close to those previously observed for intestinal injury and are among the highest observed with normal tissues. If, therefore, the RBE for oesophaged tumours follows that of the tissue of origin then oesophageal tumours would respond well to neutron therapy. However, the high RBE for the normal oesophageal damage may limit treatment at this site. Irradiation with single doses of X-rays of animals breathing oxygen or in normal air breathing conditions but after administration of the anoxic radiosensitizing drug misonidazole (Roche Products Ltd. Ro- 07-0582) both gave enhancement of damage relative to air breathing anaesthetised mice, indicating that hypoxia in these anaesthetised animals affects the sensitivity of the oesophagus to large doses of radiation.