O47. Dose-volume effects in acute reacting mouse jejunum

Abstract

Introduction Dose-volume effects imply that the tolerance of healthy organs increases when the irradiated volume decreases. These effects are important for uniform and non-uniform dose delivery in acute reacting organs like the intestinal tract, considering optimization constraints in human radiotherapy treatment planning. It is expected that other mammals, such as rodents, could exhibit similar response to radiation as humans and aid in understanding such effects. We investigate this effect in rodent jejunum. Materials and methods Mice (NIH strain & female) were sedated and had a section of jejunum extracted and irradiated. A Perspex jig allowed immobilization of the mice during irradiation. Mice were divided into groups where some received whole-body exposures, while others received a circular 5 mm or 1 × 1 cm2 field of 6 MV X-rays to the jejunum. This was done at dose levels of 8–20 Gy. Eighty-four hours later the mice were euthanized and the irradiated sections of jejunum were removed. Cross-sectional cuts of the sections were made and set onto glass slides. The number of regenerated crypts per circumference were counted and compared. Results Crypt regeneration decreased with increasing dose levels. Significant differences in the number of regenerated crypts were found in the 5 mm field compared to the whole-body and 1 × 1 cm2 field. The recovered dose (Dose1-Dose2) expressed at the level of 50 regenerated crypts, was 3.55 Gy. These results demonstrated the presence of a critical local migration distance for cells in the regeneration process. Conclusion The 5 mm field irradiations appeared to have had a greater regeneration capacity compared to the larger fields. This suggests that a non-local repair mechanism, acting from the surrounding non-irradiated tissue, may aid in the repair of small irradiated volumes. However the 1 × 1 cm2 field results suggests that repair capacity is greatly reduced beyond a certain critical distance.