Loss of reirradiation tolerance in the kidney with increasing time after single or fractionated partial tolerance doses

The aim was to determine the influence of initial dose and dose per fractionation on retreatment tolerance of the kidney. Mouse kidney was bilaterally irradiated with various single or fractionated X-ray doses equivalent to about 12-70% of a defined response dose. The mice were retreated with a range of single dose after 2 or 26 weeks. The development of functional kidney damage was followed by monthly testing of clearance of 51CrEDTA until the animals expressed overt renal dysfunction (maximum follow-up 70 weeks after retreatment). Doses required to give a 50% incidence of damage (RD50) were compared for animals that had received previous single dose or fractionated irradiations, or that were previously unirradiated. Multivariate analysis of time to expression of renal damage (latency) was also done using the Cox Proportional Hazards model. (author)