The effect of irradiated volume on the chronic radiation damage of the rat large bowel.

PURPOSE

The dependence of the structural and the functional chronic radiation damage in the large bowel of rats was investigated in order to develop criteria for optimising treatment plans.

MATERIAL AND METHODS

Rats were locally irradiated to different volumes of their rectum. The resulting chronic damage was determined by clinical observation, by rectoscopy and by histopathology.

RESULTS

The structural damage as well as the functional damage depend very much on the dose distribution in the large bowel, however, this influence is different for structural and for functional damage expression. Much less field size effect was seen for the structural damage of ulceration than for the functional damage of rectal obstruction when the length of whole circumference irradiation was reduced or when only half of the circumference was irradiated.

CONCLUSIONS

Different criteria are likely to apply for different types of damage even in one particular organ. The volume or the proportion of an organ which receives the target dose is not always a useful criterium for optimizing treatment plans.