THERMORADIATION THERAPY FOR SUPERFICIAL MALIGNANT-TUMORS

Background. Between 1980-1990, 126 patients were treated with radiatio n therapy (RT) and hyperthermia using 915-MHz external microwave appli cators. All but 11 patients had failed to respond to previous therapy. Methods. The mean tumor volume was 73 +/- 13 cm3, and the mean radiat ion dose delivered was 45 +/- 1 Gy. Hyperthermia was administered biwe ekly in 83% of the fields in 5.5 +/- 0.2 sessions. Lesions were strati fied by depth. The predictive influence of pretreatment or treatment p arameters was analyzed for the probability of response by logistic reg ression and for the duration of local control by proportional hazards. Results. In tumors considered potentially heatable (i.e., less-than-o r-equal-to 3-cm deep), the complete response (CR) rate was 70%, wherea s the CR rate for patients with tumors deeper than 3 cm was 18% (P < 0 .0001). Among superficial lesions of less than or equal to 3-cm depth that exhibited a CR, 14 recurred (26%, 8.7 +/- 1.6 months), while 39 l esions were recurrence-free at last follow-up of 17.8 +/- 1.4 months. The 50% tumor-effective dose was 44 Gy. For superficial lesions that r eceived between 30-60 Gy, the CR rate was 55% when the fraction size w as less than 3 Gy, whereas it was 77% when the fraction size was 3-4 G y (P = 0.05). Multivariate logistic regression analysis indicated that the model best correlating with CR included concurrent radiation dose (P = 0.006) and tumor volume (P = 0.02; model P = 0.0001). Multivaria te proportional hazard analysis indicated that the model best correlat ing with duration of local control included tumor histology (P = 0.004 ; model P = 0.0007). The overall survival rate of patients with lesion s of less than or equal to 3-cm depth who were treated with thermoradi ation therapy was 16.1 +/- 1.2 months. For patients with lesions more than 3-cm deep, survival was 8.7 +/- 1.1 months (P < 0.001). Forty-two fields were treated without any skin reactions (33%), 59 exhibited er ythema (47%), and 25 experienced thermal blistering (20%). Conclusions . Treatment of superficial malignant tumors can benefit from the adjuv ant use of hyperthermia delivered with external 915-MHz applicators pr ovided tumors are less than 3 cm from the surface and the lateral marg ins are within the 50% specific absorption rate (SAR) on the surface.