Bath and Shower Effect in Spinal Cord: The Effect of Time Interval

Purpose To evaluate the time dependency of the sensitizing effect of a large low-dose field on a small high-dose field in the rat cervical spinal cord. Methods and materials Irradiation experiments with a relatively low dose to a large volume (bath, 2 cm, 4 Gy) were combined with high doses to a small volume (shower, 4.7 mm, 26–43 Gy) at intervals of 8 minutes and 3, 12, and 24 hours. Both a functional score defined as motor impairment and a histologic score characterized as white matter necrosis were used as end points. Results Application of the 4-Gy bath dose resulted in a significant decrease in 50% isoeffective dose (ED50 ) from 48.7 Gy (small field) to 40.8 Gy. If the interval was extended, the ED50 increased to 44.4 (3 hours) and 44.8 Gy (12 hours), whereas a 24-hour interval resulted in a significant increase to 51.9 Gy. If the histologic end point was considered, the ED50 for all dose–response curves decreased slightly with 0.2 to 2.6 Gy without significantly changing the kinetics. Conclusions The bath effect as applied in the bath-and-shower experiment lasted for at least 12 hours and disappeared in the 24-hour interval. This time scale clearly deviates from the repair kinetics in spinal cord derived from low-dose-rate and fractionated irradiations.