Radiation tolerance of the XXXX rectum to fractionated X-rays and pi-mesons.

@entity697 @entity82 @entity12478 @entity1317 @entity1066 @entity33 @entity292 @entity35 @entity8638 @entity130
A 2.5 cm segment of the rectum of female F344 @entity35 was irradiated with up to 10 fractions of X-rays or pions. Transient signs of @entity697 were followed by chronic @entity130 starting at about 2 months. @entity12478 were frequently observed in animals with severe @entity8638 . Two patterns of @entity8638 were observed, an early type consisting of deep @entity1066 and @entity292 , and a late type characterized by @entity1317 , @entity82 and @entity33 . In a 4-fraction X-ray experiment, the influence of a low-residue diet was compared with a regular diet, showing no significant differences in pathology or survival. Isoeffective doses were determined for the occurrence of severe @entity130 at 250 days. Fitting the data to an LQ-model yielded an alpha/beta ratio of 13 Gy for pions, and 6.5 Gy for X-rays. Increasing the overall treatment time from 9 days to one month gave a significant rise in isoeffective doses for @entity8638 . This suggests that the more delayed types of injury did not develop independently from the acute mucosal changes. The RBE of pions for @entity130 at 250 days was 1.2 for single doses, increasing to about 1.4-1.5 at a dose per fraction of 4 Gy. These values are similar to those obtained in other acute and late responding tissues.
