Thermoradiation therapy for superficial malignant tumors

Between 1980-1990, 126 patients were treated with radiation therapy (RT) and hyperthermia using 915-MHz external microwave applicators. All but 11 patients had failed to respond to previous therapy.

The mean tumor volume was 73 +/- 13 cm3, and the mean radiation dose delivered was 45 +/- 1 Gy. Hyperthermia was administered biweekly in 83% of the fields in 5.5 +/- 0.2 sessions. Lesions were stratified by depth. The predictive influence of pretreatment or treatment parameters was analyzed for the probability of response by logistic regression and for the duration of local control by proportional hazards.

In tumors considered potentially heatable (i.e., < or = 3-cm deep), the complete response (CR) rate was 70%, whereas 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 lesions 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 received between 30-60 Gy, the CR rate was 55% when the fraction size was less than 3 Gy, whereas it was 77% when the fraction size was 3-4 Gy (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). Multivariate proportional hazard analysis indicated that the model best correlating with duration of local control included tumor histology (P = 0.004; model P = 0.0007). The overall survival rate of patients with lesions of less than or equal to 3-cm depth who were treated with thermoradiation 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 erythema (47%), and 25 experienced thermal blistering (20%).

Treatment of superficial malignant tumors can benefit from the adjuvant use of hyperthermia delivered with external 915-MHz applicators provided tumors are less than 3 cm from the surface and the lateral margins are within the 50% specific absorption rate (SAR) on the surface.