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A total of 38 patients with 81 multiple neck node metastases from squamous cell carcinoma of head and neck were treated with radiotherapy alone or with radiotherapy plus hyperthermia. Irradiation was delivered following a three fractions per day schedule of 2 + 1.5 + 1.5 Gy/day, with 4 h intervals between fractions, up to a total dose of 60 Gy. Heat was applied by means of a 500 MHz apparatus. Temperature data were converted to equivalent minutes at 42.5 degrees (Eq 42.5). Initial complete response rates and local control distribution were compared for subgroups of tumour volume and thermal dose. The data indicated that the volume effect was less pronounced in the combined modality than in the radiation alone arm, suggesting that the addition of heat was more damaging to the large than to the small lesions. A striking thermal dose-response relationship was shown, although complete response rates increased only after a certain thermal dose was accumulated, clearly indicating the presence of a threshold dose.

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Site-and tumor-specific data obtained from two groups of patients with head and neck and melanoma lesions, respectively, showed that both immediate response and response duration were enhanced by the addition of heat. Two important variables, however, such as tumor volume and "isoeffect thermal dose" appeared to influence local tumor control. The volume effect was less pronounced in the lesions treated with radiotherapy plus heat than in those treated with radiotherapy alone, suggesting that the addition of heat was more damaging to the large than to the small lesions. Furthermore, a striking isoeffect thermal dose-response relationship was shown in head and neck lesions. Those data were collected and used to design a mathematical model relating the probability of local control to clinical and treatment variables. The analysis shows that, by using the same radiation parameters, the probability of local tumor control is a function of both "isoeffect thermal dose" and tumor volume. Cancer 60:950-956,1987. HE CLINICAL EXPERIENCE accumulated in recent T years has clearly shown the potential of using hy-perthermia in addition to radi~therapy.'-~ Despite the inhomogeneity of patient population under treatment with regards to tumor size, location and histology, the results of all published studies have been surprisingly consistent in showing a constant therapeutic benefit of the combined modality over radiation alone.2 However, the information on specific tumor site and histology as well as the duration of the heat improved radiation response is limited5-' and deserves more careful investigation. The aim of this report is to discuss the results of the various treatment schedules, and to examine the mechanisms and factors affecting tumor response in general, as well as to provide site-and tumor-specific data with respect to initial response and response duration. Materials and Methods This study comprised 38 patients with 81 multiple neck node metastases from squamous cell carcinoma of

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