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.

[Chronic radiation sequelae in the rat rectum following intracavitary irradiation with different doses]. / Chronische Strahlenfolgen am Enddarm der Ratte nach intrakavitärer Bestrahlung mit unterschiedlicher Dosisleistung.

The dependence of chronic radiation damage of the rectosigmoid on dose, dose rate and irradiated volume after intracavitary irradiation with an oscillating iridium source was studied in rats. The incidence of large bowel stenosis increased with increasing dose, dose rate and volume. The nominal dose leading to 50% incidence of stenosis was 27 Gy at 2 Gy/min, 32.5 Gy at 0.2 Gy/min and 51 Gy at 0.05 Gy/min.

Radiation-induced heart disease in rats.

After local irradiation of the rat heart with X ray doses of over 10 Gy (single dose), animals developed symptoms of radiation-induced heart disease, which at higher doses would lead to fatal cardiac failure. The LD 50 at 1 year was between 15 Gy and 20 Gy. The pericardium and epicardium responded to irradiation with exudative pericarditis after 4 months. Focal myocardial damage was secondary to progressive capillary damage.

Large bowel stenosis in rats after fractionated local irradiation.

After local irradiation of the distal large bowel rats may develop fatal large bowel stenosis within 200 days. The incidence rises steeply with dose. The LD50 for single dose irradiation is 20 Gy. The tolerance of the large bowel to local irradiation depends strongly on dose fractionation. Extending the intervals between the fractions and decreasing the dose per fraction both have a pronounced dose-sparing effect.