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The Utility of Thermal Dose as a Predictor of Tumor and Normal Tissue Responses to Combined Radiation and Hyperthermia¹

Division of Radiation Oncology, Department of Radiology, University of Arizona Health Sciences Center, Tucson, Arizona 85724

A total of 236 dogs and cats with a variety of cancers were randomized to receive radiation (XRT) or heat plus XRT. In those tumors which were heated, thermal gradients developed which varied in temperature minima and maxima. The influence of the thermal gradient characteristics on tumor and normal tissue responses was examined by correlation of response with the magnitude of gradient minima and maxima. Using multivariate analysis, the influence of other factors such as tumor histology, volume, site, heat treatment method, and number of heat fractions on tumor response was examined.

Of all factors examined, tumor volume and non-site-specific average minimum equivalent min at 43° emerged as consistent predictors of both complete response rate (p < 0.001) and duration response (p < 0.05).

No significant enhancement of moist desquamation or late fibrosis was seen for heat + XRT versus XRT alone. The incidence of direct thermal injury to skin was positively correlated with maximum intratumoral equivalent min at 43°. These results indicate that a therapeutic gain is achievable with heat + XRT, but successful application of the therapy is dependent on achieving high tumor thermal gradient minima and low maxima.

¹ Presented at the Workshop Conference on Hyperthermia in Cancer Treatment, March 19 to 21, 1984, Tucson, AZ. This work was supported by Grants CA 17343 and CA23074 from the National Cancer Institute, NIH.

² To whom requests for reprints should be addressed at: Duke University Medical Center, Radiation Oncology, Box 3085, Durham, NC 27710.