Microwave-induced hyperthermia and ionizing radiation. Preliminary clinical results

Clinical research into hyperthermia treatment of cancer using a 430 MHz microwave heating system with a lens applicator

Tokyo Metropolitan Komagome Hospital, Kyoto University Hospital, and Aichi Cancer Center used a lens applicator microwave equipment, the HTS-100, to treat 90 patients with a total of 96 tumours. The results were analysed, and the following conclusions reached. Three clinical cases have been presented to illustrate the features of the HTS-100. (1) The results of 383 heating sessions using the HTS-100 were analysed. Even tumours larger and deeper than 5 cm could be heated above 42 degrees C. The heating area is much wider than that of the other 2450, 915, 430 MHz microwave heating equipments. (2) Hyperthermia treatment using the HTS-100 was combined with radiotherapy. The percentage effectiveness in terms of CR+PRa was 66.3% for the 89 cases which could be evaluated. Even for tumours larger than 5 cm, and deeper than 4 cm, local control was achieved in 60.7%. Thus, the indications for microwave heating have been significantly expanded. (3) Combination of microwave heating and RF heating is a new protocol which also expands the indications for hyperthermia therapy. (4) The percentage of patients experiencing the side-effects of pain, a sensation of heat, and burns was 15.6%, 6.3%, and 3.6%, respectively. Most of these side-effects were mild and temporary. The percentage of patients experiencing pain was higher than in conventional microwave heating, probably because the area of heating was wider. (5) In the future, the HTS-100 can be expected to play an important role in clinical cancer hyperthermia.

Arterial rupture after microwave-induced hyperthermia and radiotherapy. With reference to two patients treated for recurrence in previously operated and irradiated areas

Two patients who developed frank arterial bleeding after combined microwave-induced hyperthermia and radiotherapy are described. One patient received re-irradiation and hyperthermia for recurrent metastatic neck nodes of a mesopharyngeal carcinoma. Full course radiotherapy had been given 6 years previously and a right-sided radical neck node dissection had been performed 4 months earlier because of recurrent neck node metastases. Six weeks after the combined therapy for a second recurrence, which achieved complete remission, a fatal rupture of the carotid artery occurred. The other patient received re-irradiation and hyperthermia for a chest wall recurrence of a breast carcinoma, treated 5.5 years previously by sector resection and tangential beam radiotherapy, and treated again 2 years earlier with extensive surgery for a local recurrence. A frank arterial bleeding from the treated region was seen after 7 months, but could be arrested with surgery. This important complication in combined hyperthermia and radiotherapy does not seem to have been recognized before. Different explanations are discussed, such as the previous local treatment as well as high temperature and atherosclerosis per se.

Results of a non-controlled trial of hyperthermia combined with radiation for superficial tumours

Fifty-four patients with 65 superficial malignant lesions were treated by local hyperthermia combined with radiation therapy at the National Cancer Center Hospital, Tokyo. Hyperthermia was delivered with an Aloka Model HMS-020 (2450 MHz) or with a horn-type applicator of BSD-1000 (80-90 MHz). Relatively small tumours, those less than 4 cm in thickness, were treated by using 2450 MHz while 80-90 MHz delivered through the horn-type applicator was used for tumours exceeding 5 cm in thickness. The radiation dose was 4 Gy twice a week or 2 Gy five times a week, the total dose being 40-60 Gy. A total of six to 10 hyperthermia treatments ranging from 40 to 60 min each, with the tumour heated to more than 42.5 degrees C, were given twice a week within 1 h following radiation therapy. Complete response was achieved in 16 of the 30 patients (55 per cent) treated with the 2450 MHz microwave, and partial response in seven others (23 per cent). Tumours treated with the BSD-1000 achieved complete response in 10 out of 33 patients (30 per cent) and partial response in nine others (27 per cent). In five out of nine patients classified as partial responders, however, complete disappearance of tumour cells was noted by post-treatment histological examination. Complete plus partial response rates were thus essentially the same with the Aloka HMS-020 and the BSD-1000, though the rate of complete response was apparently higher with the Aloka unit, probably because it was used on smaller tumours.

Microwave-induced hyperthermia and radiotherapy in human superficial tumours: clinical results with a comparative study of combined treatment versus radiotherapy alone

Eighty-five evaluable superficial recurrent malignant tumours, mainly adenocarcinomas (78 per cent), in 38 patients were treated with either combined local hyperthermia (41-45 degrees C for four sessions) and low dose radiotherapy (30.0 Gy) or the same low dose radiotherapy alone. The treatment was given for two weeks. Hyperthermia was induced externally with 2450 MHz or 915 MHz microwaves. Totally 57 tumours were given combined treatment with a complete and partial response rate of 46 and 30 per cent, respectively (duration 1-38 months). In 18 patients with 2-10 superficial tumours each, 56 tumours were used in a comparative study, comparing the effect of combined hyperthermia and low dose radiotherapy versus the same low dose radiotherapy alone, the patients acting as their own controls. The total response rates were 89 and 50 per cent, respectively, in the two treatment modality groups. The difference in response rates is significant (p = 0.0039) in favour of the combined treatment, and this is also found when comparing complete remissions only (p = 0.0027). Local pain and normal tissue reactions presented problems during and after 2450 MHz microwave-induced hyperthermia treatment, performed without a coupling water bag system. Introduction of 915 MHz microwave-induced hyperthermia with a coupling deionized water bag system and refinement of microwave applicators, as well as the temperature control system considerably reduced these problems.

Computer controlled microwave system for clinical hyperthermia

A hyperthermia system which has been developed for clinical use is described. Different direct-contact applicators working at the ISM microwave frequency of 915 MHz are used for inducing heat in superficial tumours to a depth of about 3 cm. The system is a further development of an earlier prototype which worked at 2450 MHz. The microwave generator is controlled by a microcomputer governed by temperature measurements with thermistor probes inserted into the tissue. To minimise the influence of the interaction between the microwaves and the temperature probes, a pulsed irradiation technique is used. Up to July 1984, 80 superficial tumours had been treated with radiotherapy combined with local hyperthermia applied using this system.

Absorbed power distributions from two tilted waveguide applicators

One major problem in microwave-induced clinical hyperthermia treatment of superficial tumours is to obtain therapeutic temperatures at the tumour periphery and adequate deep heating when using a single applicator. The use of multiple applicators has therefore been investigated in order to improve the power distribution. Anatomical surface topography often permits the application of two tilted applicators, e.g. in the head and neck area, on extremities and on large protruding tumours. Theoretical calculations of the absorbed power distribution from such an applicator configuration were performed in a homogeneous muscle equivalent medium. The power distribution from two conventional radiative apertures (TE10) was studied at different frequencies, aperture sizes, tilting angles and non-coherent or coherent fields in phase, both theoretically and with phantom experiments using a thermographic camera. With controlled phase relations between two tilted applicators excited at the lower microwave or upper radiofrequency band, the absorbed power distribution can be varied in a wide range. The theoretical calculations and thermographic phantom experiments in simple geometries give valuable information on absorbed power distributions and guidance for the location of temperature probes in clinical hyperthermia.

Response to heat treatment (42.5 degrees C) in vivo and in vitro of five human melanoma xenografts

The response to heat (42.5 degrees C) of five human melanoma xenografts was studied. Tumours grown subcutaneously in the hind leg of athymic mice were heated in a water-bath and specific growth delay was used as a measure of response. In other experiments, cells from the same xenografts were heated in vitro and the colony-forming ability was assayed in soft agar. The slopes of the in-vivo dose-response curves (specific growth delay versus heating time) varied within a factor of about three among the five melanomas. The Do values of the in-vitro heat survival curves ranged from 44 +/- 3 to 123 +/- 15 min. The response to heat in vivo was not positively correlated with the tumour volume-doubling time, the growth fraction, the cell loss factor or the intrinsic heat sensitivity of the tumour cells, i.e., the Do values of the in vitro heat survival curves. If the results obtained in the present work are representative for clinical practice, they indicate that the response to heat may vary considerably among tumours in different patients. This variability can probably not be predicted from measurements of cytokinetic parameters of the tumours. The lack of correlation between the response to heat in vivo and in vitro demonstrates that extrapolations of results from studies in vitro to tumours are highly speculative and, when attempted, should be executed only with extreme caution.

Technique for microwave-induced hyperthermia in superficial human tumours

In order to induce local hyperthermia in superficial tumours a computer system using a 2,450 MHz microwave generator connected to a circular (diameter 90 mm) direct contact applicator was constructed based on invasive temperature control. Small thermistor probes with a diameter of 0.6 mm are inserted in the tumour and surrounding tissues. Eight thermistors can be used simultaneously and one of them is chosen as the "master'. The automatic control system used a pulsed irradiation technique to avoid the problem with interactions between the metallic wires of the temperature probe and the electromagnetic field. With the system it was possible to control the temperature at the master thermistor within +/- 0.5 degrees C from the preset value.