Modification of radiation damage in the canine kidney by hyperthermia: A histologic and functional study

The purpose of the present study was to evaluate the effect of hyperthermia on the histologic and functional response of the canine kidney following bilateral renal irradiation and hyperthermia. A preliminary investigation also documented renal temperature during whole body hyperthermia (WBH). Thirty-six Beagles were randomized to the following 6 treatment groups: control, WBH alone, 10 Gy alone, 10 Gy + WBH, 15 Gy alone, and 15 Gy + WBH. Whole body hyperthermia was used to produce hyperthermia to insure renal temperatures of 42.0 to 42.5C. These temperatures were reached approximately 90 minutes after completion of radiotherapy and were maintained for 60 minutes. Radiation was delivered as a single fraction. Renal histologic and functional changes were assessed at 1, 2, 3, 4, 6, and 9 months posttherapy. A modified Chalkley point count technique was used to estimate renal tubular, interstitial, vascular, and glomerular volumes. Glomerular filtration rate (GFR) which indicates renal function was measured by clearance of m99Tc-DTPA using a gamma camera. No changes were seen in GFR or renal tissue volumes in control or WBH alone groups. Renal vascular and glomerular volumes were not affected significantly by any combination of hyperthermia and radiation. In all groups receiving radiation, GFR decreased, percent renal tubular volume decreased and interstitial volume increased significantly over time posttherapy. The magnitude of these changes in the functional and histologic response of the kidney and the latency period before expression of this damage was radiation dose-dependent. Hyperthermia did not modify radiation damage in the kidney as measured with functional and histologic endpoints chosen for this study