Beam shaping for microwave waveguide hyperthermia applicators

PURPOSE

Hyperthermia treatments commonly use single element microwave waveguide applicators. The microwave beam patterns produced by these applicators are often non-uniform. As a result, hot spots are formed in the heated tissue and therapeutic temperatures are reached in only small areas of the treatment field. We have constructed new coupling boluses that improve the heating patterns of external microwave applicators.

METHODS

The microwave beam transmitted through the bolus is modified by microwave absorbing saline/gelatin pads. The pads can be designed to result in a uniform heating pattern over a large area or alternatively, complex heating patterns can be generated for specific clinical applications. An analysis of the effect of bolus design parameters on microwave absorption patterns is presented. The heating patterns of the MA-100 and MA-120 microwave waveguide applicators have been measured in muscle and fat phantom materials with both the manufacturer's boluses and the new boluses.

RESULTS

In the case of the MA-100, the area above the 70% heating level measured in a muscle phantom was increased by a factor of 2.3 by an absorbing pad bolus. Similarly, the heating area of the MA-120 was increased by a factor of 2.6 by an absorbing pad bolus. The boluses were tested in a clinical setting by measuring tissue temperature profiles in patients under different bolus arrangements. The area over which therapeutic temperature was achieved was increased considerably when the absorbing bolus was used. A second bolus was designed for the MA-120 to produce a ring heating pattern for the treatment of a breast cancer patient who had developed recurrences at the periphery of a skin graft. The heating pattern produced in a muscle phantom is compared with tissue temperature profiles measured during the hyperthermia treatment of this patient.

CONCLUSIONS

Microwave absorbing filters using saline pads significantly improve the heating patterns of microwave waveguide hyperthermia applicators. This improvement was confirmed in clinical application where much greater areas of homogeneous heating were observed. The technology was extended to produce complex heating patterns for special clinical applications.

Primary carcinoma involving the petrous temporal bone

Between 1975 and 1985, 29 patients with the diagnosis of carcinoma of the petrous temporal bone were seen at the Princess Margaret Hospital. Twenty-seven carcinomas were graded: 13 were well-differentiated; the remaining 14 were either moderately or poorly differentiated tumors. Fifteen patients were managed with a combination of surgery and radiotherapy, 13 were treated with radiotherapy only, and one patient was treated by surgery alone. Median follow-up time was 6.1 years, and the 5-year actuarial local control and cause-specific survival rates for the entire group were 40% and 50%, respectively. Age greater than 60 years, poor grade of tumor, and involvement of the facial nerve were three significant variables associated with poor outcome. A superior 5-year actuarial local control was achieved with surgery plus postoperative radiotherapy (54%) compared to other treatment approaches. Based on the results from this review, we would continue to recommend a combined modality approach of surgery followed by postoperative radiotherapy in the management of this rare, but life-threatening disease.

Postradiation dental extractions without hyperbaric oxygen

This study examined the incidence of osteoradionecrosis after tooth extraction with low-epinephrine or epinephrine-free, nonlidocaine local anesthetics and conservative surgical techniques. Estimates of the absorbed radiation dose on irradiated alveolar bone were made by reviewing radiotherapy records. This investigation included 72 patients ranging in age from 22 to 80 years (median 57.4 years). We removed 449 teeth. Analysis of radiotherapy check films revealed that only 196 teeth (44%) were included within the treatment volume. The median prescribed tumor dose was 50 Gy (range 25 to 84 Gy) in 20 fractions (range 10 to 37), with a median dose per fraction of 2.5 Gy (range 1.88 to 3.14 Gy). Follow-up time ranged from 68 days to 19.3 years (median 4.8 years). No instances of osteoradionecrosis occurred as a result of dental extraction with this conservative method.

A management approach to incompletely excised basal cell carcinomas of skin

There were 187 incompletely resected basal cell carcinomas (BCC) of skin referred to the Princess Margaret Hospital between 1970 and 1985. Median age at presentation was 62 years. The commonest location of these lesions was in the head and neck region (93%). One hundred twenty lesions were immediately treated: 119 were irradiated and 1 was excised. The remaining 67 lesions were managed expectantly. Follow-up time for the entire population ranged from 1 month to 17 years, with a median time of 2.7 years. The 5-year probability of remaining relapse-free in the group immediately treated was 91% versus 61% if managed expectantly (p = 0.0001). If only lateral margins were positive, the crude probability of local failure was 3/18 (17%), versus 9/27 (33%) if the deep margins were involved (p = 0.2). Once relapse occurred in the group of lesions treated expectantly, 17/20 (85%) of these relapses were salvaged by either radiation or surgery. The 10-year actuarial probability of local control for the lesions immediately treated and observed were similar: 92% and 90%, respectively (p = 0.5). An economic analysis revealed that immediate radiation treatment saved the health system only $223.00 per patient. Since there is no difference in the ultimate local control between these two approaches, and these elderly patients may be spared the morbidity of unnecessary treatments, it is suggested that a policy of observation may be adopted for basal cell carcinomas of skin which have been incompletely excised.

Important prognostic factors influencing outcome of combined radiation and hyperthermia

Clinical experience with combined local-regional hyperthermia and radiation therapy has been rapidly accumulating over the past few decades. Its superior efficacy to the use of radiation alone has been demonstrated in several retrospective and prospective reports in the literature. It is evident now that there are several important factors that will influence the final outcome of the treated patients. The parameters that will be discussed in this paper include: I. Pretreatments factors: 1. tumor dimension 2. tumor histology 3. tumor site. II. Treatment factors: 1. radiation therapy dose 2. hyperthermia parameters: (a) thermal variables (b) number of heat treatments (c) sequence of hyperthermia and radiation treatments (d) hyperthermic device. Finally, evaluation of response and complications will also be discussed. The importance of abiding by an accepted reporting system will be emphasized, and clarification of times at which response assessments were made will also be discussed. With the availability of longer term follow-up, use of an actuarial method of reporting becomes more important. The future of hyperthermia and radiation remains very promising but a lot of questions still need to be answered by well-conducted and reported clinical trials.

Bladder cooling in patients treated with regional hyperthermia of the pelvis using an annular phased array

Regional hyperthermia for the treatment of deep seated tumors is often limited by excessive heating of normal tissues, usually with associated patient pain and/or discomfort. The use of bladder cooling via perfusion of distilled water through a modified tri-lumen irrigation catheter as an aid to circumventing this problem in one anatomical region is described. This relatively simple technique provided rapid pain relief and permitted completion of the hyperthermia treatment in a satisfactory manner. Modifications of this technique may permit selective heating and/or cooling of the bladder during regional hyperthermia treatments in the pelvis.

Primary lymphoma of the breast

Primary lymphoma of the breast is a rare entity. This paper adds a further 16 cases to the world literature. Axillary nodal status appears to be an important prognostic factor for survival. Stage IE patients should be treated with an excisional biopsy followed by radiation to the breast and to the regional nodes. Combined treatment with systemic chemotherapy with local irradiation should be considered for patients with Stage IIE disease (breast and axillary nodes).