Effects of volume irradiated on the function of the canine ureter.

This study was designed to investigate the influence of the volume irradiated on the probability of ureteral complications and to provide data for volume modeling. One hundred thirty-four purpose-bred beagle dogs received single intraoperative doses of 6 MeV electrons ranging from 12 to 54 Gy to three lengths of ureter: 2, 4 or 8 cm. The response was evaluated by excretory urography. The ED50 was 21.9 Gy (95% CI 13.3-30 Gy) for 8 cm 3 years after treatment. The estimated ED50's were greater than 43 Gy for 4 cm and 85 Gy for 2 cm. Reducing the length of ureter irradiated from 8 cm to 4 cm increased the ED50 for ureteral dilation by at least a factor of 2, while reduction from 8 cm to 2 cm increased the ED50 by at least a factor of 4. The ED50 for renal injury secondary to stenosis was 30.5 Gy (95% CI 17.2-232 Gy) when an 8-cm field was irradiated. There was a significant effect of volume irradiated on the frequency of ureteral stenosis. Reducing the length of ureter included in the treatment field should allow delivery of higher doses to tumors without increased complications.