Optimization of hyperthermia with CT scanning

An adaptive microwave phased array for targeted heating of deep tumours in intact breast: animal study results

It has previously been reported in phantoms, that an adaptive radiofrequency phased array can generate deep focused heating distributions without overheating the skin and superficial healthy tissues. The present study involves adaptive microwave phased array hyperthermia tests in animals (rabbits) with and without tumours. The design of the adaptive phased array as applied to the treatment of tumours in intact breast, is described. The adaptive phased array concept uses breast compression and dual-opposing 915 MHz air-cooled waveguide applicators with electronic phase shifters and electric-field feedback, to focus automatically by computer control the microwave radiation in deep tissue. Temperature measurements for a clinical adaptive phased array hyperthermia system demonstrate tissue heating at depth with reduced skin heating.

Biological rationale and clinical experience with hyperthermia

Hyperthermia (HT) as an adjunct to radiation therapy (RT) has been a focus of interest in cancer management in recent years there have been numerous randomized and nonrandomized studies conducted to assess the efficacy of HT combined with either RT or chemotherapy especially in the treatment of superficially seated malignant tumors. The major impact of HT is currently on locoregional control of tumor. Heat may be directly cytotoxic to tumor cells or inhibit repair of both sublethal and potentially lethal damage after radiation. These effects are augmented by the physiological conditions in tumor that lead to states of acidosis and hypoxia. Blood flow is often impaired in tumor relative to normal tissues, and HT may lead to a further decrease in blood flow and augment heat sensitivity. Three major areas of clinical investigation have borne the greatest fruit for HT as adjunctive therapy to RT. These include recurrent and primary breast lesions, melanoma, and head and neck neoplasms. Thermal enhancement ratio was increased in all cases and is approximately 1.4 for neck nodes, 1.5 for breast, and 2 for malignant melanoma. In general, the most important prognostic factors for complete response (CR) are RT dose, tumor size and minimal thermal parameters minimal thermal dose (t43min), mean minimal temperature (Tmin) or T90, i.e., temperature exceeded by 90% of thermal sensors]. The number of HT fractions administered per week appears to have no bearing on the overall response, which may be indicative of the effects of thermotolerance. The total number of HT fractions delivered also appears irrelevant provided adequate HT is delivered in one or two sessions. The major prognostic factors for the duration of local control were tumor histology, concurrent RT dose, tumor depth and Tmin. Although numerous single institution studies showed increased CR rates and improved local control, the efficacy of HT as an adjunct to RT should be assessed with well-designed multi-institutional randomized clinical trials. Such clinical trials are underway.

Predictive factors for skin reactions in patients treated with thermoradiotherapy

In this study we performed univariate analyses to analyse the predictive factors for skin reactions, i.e. erythema, thermal blisters and ulceration, that occur during thermoradiotherapy. One hundred and twenty-six fields in 126 patients were treated with thermoradiotherapy using 915 MHz external microwave hyperthermia. Mean age of patients was 62 years. All but 11 lesions received previous therapy. Prior treatment included surgery (75%), chemotherapy (60%) and/or radiation therapy (51%). The mean previous radiation dose was 54 +/- 2 Gy. The concurrent tumour radiation dose was 45 +/- 1 Gy, in 16 fractions, over 35 elapsed days (dose per fraction of 1.6-4.8 Gy). The mean number of heat sessions administered was 5.5 +/- 0.2 (range 1-14). In 83% of cases hyperthermia was administered biweekly. Forty-two patients were treated without any skin reaction (33%), erythema occurred in 59 fields (47%), transient thermal blisters occurred in 25 fields (20%) and ulceration occurred in 23 fields (18%). In 25 cases, two or more skin reactions (20%) were observed concurrently. Concurrent radiation dose correlated with skin reactions (p = 0.02). The incidence of skin reactions was inversely correlated with previous radiation therapy (p = 0.04) and previous radiation therapy dose (p = 0.04) possibly due to fibrosis. None of the tumour or skin thermal parameters correlated with the reaction rate.

Thermoradiotherapy for superficial tumour deposits in the head and neck

Tumour deposits in the head and neck region were treated with hyperthermia using 915 MHz external microwave applicators and radiation therapy between 1986 and 1990. The mean (+/- SE) radiation dose was 47 +/- 2 Gy (range 21-77 Gy). All but four patients had failed previous therapy. Mean tumour volume was 40 +/- 10 cm3 (range 0.3-276 cm3). Hyperthermia was administered biweekly in 80% of the patients in 6.0 +/- 0.4 sessions (range 1-10); thermometry involved 3.6 +/- 0.4 catheters (range 1-9) and 5.7 +/- 0.4 sensors (range 1-12) per tumour. Of the 50 lesions evaluable for response, 29 had a complete response (58%), and 20 had a partial response (40%). Lesions were stratified by depth. In tumours considered potentially heatable (i.e. depth < or = 3 cm and lateral dimensions at least 2 cm less than boundary of applicator), the complete response rate was 81% (26/32, 47 +/- 2 Gy, 15 +/- 3 cm3); whereas for patients with tumours deeper than 3 cm, the complete response rate was 17% (3/18, 48 +/- 3 Gy, 110 +/- 21 cm3), p = 0.0001. Among lesions < or = 3 cm depth that exhibited a complete response, six recurred (24%, 5.8 +/- 1.8 months) while 20 lesions were recurrence free at last follow-up of 11.9 +/- 1.2 months). The overall survival of patients with lesions < or = 3 cm depth was 11.5 +/- 1.3 months (range 2.4-32.3 months) while for patients with lesions > 3 cm depth survival was 6.7 +/- 0.9 months (range 2.1-18.6 months), p = 0.01. In superficial lesions with depth < or = 3 cm, multivariate logistic regression analysis indicated that the model best correlating with complete response included radiation dose (p = 0.08) and tumour volume (p = 0.08, model p = 0.004). Multivariate proportional hazard analysis indicated that the model best correlating with duration of local control included tumour depth (p = 0.03) and previous radiation therapy (p = 0.08, model p = 0.006). Twenty-two fields were treated without any skin reactions (39%), 23 evidenced erythema (40%) and eight thermal blistering (14%). Ulceration occurred in 11 treatment fields but in all but one of these cases the ulceration may have been due to tumour breakdown as there was direct invasion of the skin by tumour prior to the initiation of treatment. The maximal skin temperature was the best predictor of morbidity although the correlation was not statistically significant (p = 0.19).

Thermoradiation therapy for superficial malignant tumors

BACKGROUND

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.

METHODS

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.

RESULTS

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%).

CONCLUSIONS

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.