Cancer that recurs after surgery and radiation therapy remains a major problem. The claimed effectiveness of thermobrachytherapy in patients with this problem prompted the present study. Forty-six lesions (20 head and neck, 18 pelvic, seven chest wall, and one limb sarcoma) in 38 patients were treated with interstitial hyperthermia that sandwiched the use of Ir-192 with the aim of delivering 2,000-6,000 cGy, depending on prior dose and tissue tolerance. Complete regression occurred in 19 (54%) of 35 evaluable cases. More than 58,000 measured temperature points were analyzed to develop a representative quantitative measure, the "modal thermal dose," that represented the temperature reported most often during heating sessions. The pattern was plotted in each case. No significant relation was found between heating patterns and tumor response. Of all the prognostic factors studied, the radiation dose was the most significant, with a complete response rate being 78% when the total radiation dose exceeded 6,000 cGy, compared with 8% when the dose was lower than 5,000 cGy (P less than .005). The tumor volume also was important, with smaller lesions responding much better than larger ones (P = .1).