Relationship between thermal parameters and tumor response in hyperthermia combined with radiation therapy

In hyperthermia for cancer therapy, thermal parameters related to tumor response have not yet been clarified. We investigated thermal parameters that could predict tumor response to hyperthermia combined with radiotherapy in locally advanced malignancies.

Fifty-four patients with locally advanced malignancies who were treated by hyperthermia in combination with radiation therapy were enrolled in this study. Local hyperthermia was induced by ultrasound heating equipment for 60 min, within 30 min after irradiation, twice a week, for a total of six to ten sessions. Radiation therapy was administered with a conventional fractionation regimen, at a total dose of 40-70 Gy. Multi-point thermometry results were obtained with every 10-s temperature data acquisition. An average of seven interstitial sites per tumor was monitored for each treatment. Univariate logistic regression analysis was used to investigate the relationship between tumor response and minimum, maximum, and average intratumor temperature (Tmin, Tmax, Tav); the cumulative minutes of treatment at temperatures exceeded by 90%, 50%, and 10% of the measured intratumoral temperatures (T90, T50, T10); and cumulative minutes of the temperature that achieved above the index temperature value in the tumor center ((Cum min T(center) > T(index)).

Complete and partial response rates were 32.6% and 46.2%, respectively. Univariate logistic regression analysis revealed that the temperature parameters with predictive probability were highest for Cum min T(center) > 42.5 degrees C, followed by > 42 degrees C and > 41 degrees C; and T90. Cum min T(center) > 42.5 degrees C was most significantly associated with complete tumor response (P < 0.001).

These results strongly suggest that hyperthermia is a useful adjunct to radiotherapy for increasing the local control of advanced malignancies, and that Cum min T(center) > 42.5 degrees C could be an important thermal parameter for predicting tumor response.