Clinically derived dose effect relationship for hyperthermia given in combination with low dose radiotherapy

Avoiding Pitfalls in Thermal Dose Effect Relationship Studies: A Review and Guide Forward

The challenge to explain the diffuse and unconclusive message reported by hyperthermia studies investigating the thermal dose parameter is still to be unravelled. In the present review, we investigated a wide range of technical and clinical parameters characterising hyperthermia treatment to better understand and improve the probability of detecting a thermal dose effect relationship in clinical studies. We performed a systematic literature review to obtain hyperthermia clinical studies investigating the associations of temperature and thermal dose parameters with treatment outcome or acute toxicity. Different hyperthermia characteristics were retrieved, and their influence on temperature and thermal dose parameters was assessed. In the literature, we found forty-eight articles investigating thermal dose effect relationships. These comprised a total of 4107 patients with different tumour pathologies. The association between thermal dose and treatment outcome was the investigated endpoint in 90% of the articles, while the correlation between thermal dose and toxicity was investigated in 50% of the articles. Significant associations between temperature-related parameters and treatment outcome were reported in 63% of the studies, while those between temperature-related parameters and toxicity were reported in 15% of the studies. One clear difficulty for advancement is that studies often omitted fundamental information regarding the clinical treatment, and among the different characteristics investigated, thermometry details were seldom and divergently reported. To overcome this, we propose a clear definition of the terms and characteristics that should be reported in clinical hyperthermia treatments. A consistent report of data will allow their use to further continue the quest for thermal dose effect relationships.

Procedure for creating a three-dimensional (3D) model for superficial hyperthermia treatment planning

PURPOSE

To make a patient- and treatment-specific computed tomography (CT) scan and to create a three-dimensional (3D) patient model for superficial hyperthermia treatment planning (SHTP).

PATIENTS, MATERIALS, AND METHODS

Patients with recurrent breast adenocarcinoma in previously irradiated areas referred for radiotherapy (RT) and hyperthermia (HT) treatment and giving informed consent were included. After insertion of the thermometry catheters in the treatment area, a CT scan in the treatment position was made.

RESULTS

A total of 26 patients have been, thus far, included in the study. During the study period, five types of adjustments were made to the procedure: (1) marking the RT field with radioopaque markers, (2) making the CT scan after the first HT treatment instead of before, (3) using an air- and foam-filled (dummy) water bolus, (4) a change to radiolucent catheters for which radioopaque markers were needed, and (5) marking the visible/palpable extent of the tumor with radioopaque markers, if necessary. With these adjustments, all necessary information is visible on the CT scan. Each CT slice was automatically segmented into muscle, fat, bone, and air. RT field, catheters, applicators, and tumor lesions, if indicated, were outlined manually using the segmentation program iSeg. Next the model was imported into SEMCAD X, a 3D electromagnetic field simulator.

CONCLUSION

Using the final procedure to obtain a patient- and treatment-specific CT scan, it is possible to create a 3D model for SHTP.

A literature survey on indicators for characterisation and optimisation of SAR distributions in deep hyperthermia, a plea for standardisation

PURPOSE

To evaluate the predictive value of SAR indicators by assessing the correlation of a SAR indicator with the corresponding predicted temperature. Ultimately, this should lead to a number of verified SAR indicators for characterization and optimization of a predicted SAR distribution.

METHODS

A literature survey is followed by an evaluation of the SAR indicators on their functionality, using a set of heuristic classification criteria. To obtain an objective assessment of the predictive value for SAR characterisation, all SAR indicators are evaluated by correlating the value of the SAR indicator to the predicted target temperature when heated with the BSD2000 Sigma 60 applicator. Two methods were followed. First, the specificity of the SAR indicator to target temperature was assessed for each of the 36 patient-specific models, using 30 randomly chosen phase and amplitude settings. Secondly, each SAR indicator was used as a goal function to assess its suitability for optimisation purposes.

RESULTS

Only a selected number of SAR indicators correlate well with tumour/target-temperature. Hence, for target-related properties, an adequate set of SAR indicators is found in the literature. For hotspots, modifications are desirable. For optimisation purposes, improved objective functions have been defined.

CONCLUSIONS

From the correlation of the SAR indicators with tumour temperature, a preferred set of SAR indicators is derived: For target heating, 'average SAR ratio', 'Hotspot-target SAR ratio', and 'homogeneity coefficient' provide suitable objective criteria, while for hotspot reduction, 'Hotspot-target SAR ratio' is considered the most useful indicator. For optimisation procedures, 'Hotspot-target SAR ratio' is currently the most suitable objective function.

Factors influencing the outcome of radiotherapy in malignant mesothelioma of the pleura--a single-institution experience with 189 patients

PURPOSE

To determine the factors influencing the response to palliative radiotherapy (RT) in malignant mesothelioma of the pleura (MM).

METHODS AND MATERIALS

A retrospective review was conducted of the records of all patients with mesothelioma who were referred to our institution between 1979 and 1996. A total of 227 RT series were administered to 189 patients with MM. Of these, 21 patients with chest wall nodules also received concomitant local hyperthermia.

RESULTS

The median survival was 5 months from the start of RT and only 17% of patients were alive at 1 year after treatment. Chest pain and painful chest wall metastases were the main indications for RT. A higher local response rate was seen for patients treated with a 4-Gy per fraction scheme, vs. those receiving fractions of less than 4 Gy (50% vs. 39%). Pain recurrence occurred predominantly within the previous RT field, and pain recurred after a median of 69 days (range 32-363) in the group treated using 4-Gy fractions. When compared with a matched group, patients treated with combined RT and hyperthermia had higher response rates and fewer in-field recurrences.

CONCLUSIONS

RT provides local palliation in at least 50% of patients with MM who were treated using a 4-Gy/fraction scheme to a median dose of 36 Gy. The low response rates with RT alone suggest that combined RT and local hyperthermia should be further evaluated in MM.

Changes in muscle blood flow distribution during hyperthermia

Blood flow is a critical parameter for obtaining satisfactory temperature distributions during clinical hyperthermia. This study examines the changes in blood flow distribution in normal porcine skeletal muscle before, during and after a period of regional microwave hyperthermia. The baseline blood flow distribution during general anaesthesia and after the insertion of the thermal probes was established independently in order to isolate the changes due to hyperthermia. General anaesthesia alone and thermocouple insertion during anesthesia had no significant effect on the muscle blood flow distribution. Regional microwave heating generated a non-uniform blood flow distribution which was a function of the tissue temperature distribution. Blood flow was greater in those tissues samples in which higher temperatures were recorded and less in those sampled further from the applicators peak SAR (Specific Absorption Rate). The increase in blood flow appears to be primarily a local phenomenon. Although muscle blood flow may be considered to be uniform prior to heating, this does not hold during hyperthermia treatment. Therefore, the non-uniform nature of the blood distribution during heating should be incorporated into any practical bioheat transfer model.

Some characteristics of the glutathione cycle revealed by ionising and non-ionising electromagnetic radiation

The cyclic reaction of GSH-->GSSG-->GSH (designated R(exp) or R(e)) obeys the three specific features of life by producing energy in exponential quantities relative to time, is in effect irreversible and is inherited from generation to generation. In multicellular life, this reaction produces the energy for mitosis and is kept in controlled inactivity until needed to maintain perfection of form and function by energising mitosis. The immediate control of Re appears to be feedback process-dependent on the concentration of GSSG. Ultra high-frequency electromagnetic radiation of 434 MHz (UHF) will change Re from inactive to active and, in so doing, it causes resonance and/or fluorescence of the glutathione cycle which changes its radiosensitivity. Re is the primary direct target of ionising radiation and produces the energy for mitosis. Clinical observations suggest that, in the normal cell, Re is inactive and is not killed by 3 x 2700 rads or 6 x 1650 rads yet, when active, its sensitivity value (DO) is approximately 160 rads. Using the standard radiobiological equation of response to ionising radiation, it can be deduced that radiosensitive cancers have two or three Re units active per cell and radioresistance increases in proportion to the number of potentially active Re units per cell. Re appears to be the main cause of cancers' increased conductivity of electricity compared with normal tissue. In cancer therapy, UHF is the best radiosensitiser ever discovered (up to two or more decades). Re is also intelligent compared with non-exponential reactions but cannot be the basis of intellectual brain functions which must be based on non-electrical chemical processes.

Clinical experience using 8 MHz radiofrequency capacitive hyperthermia in combination with radiotherapy: results of a phase I/II study

PURPOSE

Since 1985, the University of Minnesota Hospital and Clinic has investigated the efficacy and safety of 8 MHz radiofrequency (RF) capacitive hyperthermia using the Thermotron RF-8. This study reports the thermometric and clinical results of 119 patients treated with RF hyperthermia in combination with radiotherapy (RT).

METHODS AND MATERIALS

Of 119 patients, 69 received high-dose RT and 50 patients received low-dose RT because of previous irradiation to the treatment site. The most common anatomic sites treated were within the pelvic cavity or head and neck area. Thirty-three percent and 24% of tumors treated were > 7 cm and > 10 cm in largest diameter, respectively. Forty percent of the patients had deep-seated tumors (depth > 6 cm). Hyperthermia was given as soon as possible after RT twice weekly, allowing at least 72 h between treatments. The objective was to raise intratumoral temperatures to 42-43 degrees C or above for 30-50 min while keeping normal tissue temperatures below 40-41 degrees C.

RESULTS

Of 119 patients, 40% achieved a Tmax tumor temperature of > 42 degrees C and 40% achieved 40-42 degrees C Tmax. Higher Tmax) tumor temperatures were observed as tumor size increased. Tumors > 10 cm in largest diameter had a Tmax of 42.2 degrees C. Tumor depth was not a significant factor for the tumor temperatures achieved. Of 119 patients, 11% achieved complete response and 38% achieved partial response. Of the no-response patients, 34% had symptomatic palliation and 15% had stable disease for at least 12 months after treatment. We were able to treat tumors of patients with subcutaneous fat as thick as 3 cm by precooling the fat for 20 min with 10-15 degrees C saline-filled boluses prior to the initiation of heating. During treatment, 60% of patients complained of varying degrees of pain and 19% had pain that was a factor in limiting treatment. Vital signs were relatively stable and not a factor in limiting treatment.

CONCLUSION

The Thermotron RF-8 is a useful hyperthermia device that can raise tumor temperatures to a therapeutic level (i.e., 42 degrees C) in a significant proportion of patients with superficial, subsurface, and deep-seated tumors, with minimal adverse effects, complications, and systemic stress. Further clinical studies using improved thermometry systems are warranted.

Response of 145 spontaneous canine head and neck tumours to radiation versus radiation plus microwave hyperthermia: results of a randomized phase III clinical study

The results of a phase III, clinical trial of local microwave hyperthermia (target = 2 x 44 degrees C for 30 min) and megavoltage radiation (4 x 9 Gy fractions) in the treatment of 145 naturally occurring canine head and neck cancers are reported. Patients were re-examined at regular intervals following treatment until death. The median follow up time was 90 weeks. Tumour response, patient survival and normal tissue toxicity were analysed by treatment allocation. There was no significant difference in best tumour response nor patient survival between the two treatment groups. There was no difference in acute normal tissue toxicity but there was a suggestion that patients receiving RT and HT may suffer a higher incidence of late skin reactions. Histological type and tumour volume were of prognostic significance with smaller tumours and carcinomas showing higher response rates. There were also positive associations between minimum tumour dose and best tumour response and percentage of tumour heated and best tumour response. The results of this study must be interpreted in the knowledge of limitations on the dose and fractionation schedule for radiation therapy, the small number of hyperthermia treatments applied and the variation in tumour type and size that is inevitable in a clinical study. It is concluded that the quality of hyperthermia in terms of intra-tumour temperatures and the uniformity of heating is of paramount importance in governing response to adjuvant hyperthermia.

Some practical notes on documentation of superficial hyperthermia treatment

A detailed and accurate documentation of the treatment setup of each individual hyperthermia session is extremely important for retrospective data analysis as well as treatment quality control. In this paper the relatively simple and cheap documentation system developed by the Hyperthermia Department of the Dr Daniel den Hoed Cancer Center, is presented.

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.

Innovative techniques in radiation oncology. Clinical research programs to improve local and regional control in cancer

There is a growing importance in failure analysis in cancer management. In these analyses locoregional failure as the cause of death emerges as a significant problem in many tumor sites, e.g., head and neck cancer, gynecologic cancer, genitourinary cancer. Because of these data, the radiation oncology community has attributed high priority to research efforts to improve locoregional control. These efforts include the following: (1) brachytherapy alone or with external beam radiation therapy or surgery; (2) intraoperative radiation therapy; (3) hyperthermia with radiation therapy; (4) particle irradiation (protons, neutrons, stripped nuclei, and pions); and (5) routes of administration of the treatment, including infusional (intravenous) chemotherapy with radiation therapy, intraarterial monoclonal antibodies with radionuclides, and intraarterial chemotherapy with radiation therapy. Each area of investigation is discussed.

Retrospective analysis of hyperthermia for use in the palliative treatment of cancer: a multi-modality evaluation

Forty-two patients with local or superficial metastatic or recurrent malignant tumors were treated in a non-randomized Phase I/II study to assess the tumoricidal effects of heat combined with radiation and/or chemotherapy. Radiation doses administered averaged 3130 +/- 350 cGy; chemotherapeutic agents employed included bleomycin, mitomycin-C, adriamycin, and cis-platin, heat was induced by radiative or interstitial microwave applicators operating at frequencies ranging from 95 to 900 MHz. Forty-one of the forty-two patients were evaluated for initial therapeutic effects yielding the following response distributions: local hyperthermia with radiation--42% complete response (CR), 44% partial response (PR), and 15% no response (NR); local hyperthermia with chemotherapy--0% CR, 50% PR and 50% NR. Long-term response duration was evaluated for local hyperthermia with radiation, yielding mean time to recurrence of 9.4 months for CR's and mean time to progression of 3.4 months for PR's. In retrospective analysis, we examined the correlations of previously established response-predictor variables of tumor volume and minimum thermal dose with both initial and long-term response rates. Initial complete response rates were correlated directly with non-site-specific minimum thermal dose, varied inversely with tumor volume and exhibited a positive correlation for a limited histologic type/treatment site combination. Surprisingly, long-term response did not correlate either with tumor volume or thermal dose. The frequency of thermally induced complications, which did not correlate with any measured thermal parameters, was found to be 42%, expressed on a per-patient basis.

Measurement of tumor pH during microwave induced experimental and clinical hyperthermia with a fiber optic pH measurement system

The influence of hyperthermia on tissue pH was investigated using a modified version of the fiber optic monitoring system. This newly developed system was tested for use in tissues and found to be suitable for pH measurement during microwave induced hyperthermia. The fiber optic pH probe (0.7 mm diameter) could be easily used in the electromagnetic fields produced by the microwave applicators, whereas only the display unit required some shielding. Tissue pH of experimental and clinical tumors was measured concurrently with local microwave hyperthermia treatment. The mean initial intratumor pH of a rat rhabdomyosarcoma was 7.03 (SD 0.13, n = 19) and the pH of human subcutis was 7.45 (SD 0.02, n = 8). In rat tumor a primary pH decrease was observed during heating which was fully reversed during cooling. The coefficient of temperature dependence was -0.016 pH unit/degree C (SD 0.004, n = 12). After approximately 1 hr of heating at 43 degrees C a further pH decrease of 0.1-0.3 unit occurred which was not reversed directly after treatment. Measurements during clinical local microwave hyperthermia treatments after radiotherapy revealed similar changes in pH values, primary as well as secondary. The estimated coefficient of temperature dependence for the reversible pH change, which occurred in subcutis as well as in tumor tissue, was -0.016 pH unit/degree C (SD 0.004, n = 12). The fiber optic pH measurement system is expected to be a valuable tool in the thorough investigation of temperature and time related pH changes in tumor during experimental as well as clinical hyperthermia treatment.

Quality assurance problems in clinical hyperthermia and their impact on therapeutic outcome: a Report by the Radiation Therapy Oncology Group

Since February 1981, 300 patients with superficial measurable tumors were randomized on an RTOG protocol (81-04) involving fractionated radiation therapy (4.00 Gy twice weekly for a total of 32.00 Gy), either alone or followed immediately by hyperthermia (42.5 degrees C, 60 min). This is a report of 218 eligible patients with single lesions: 107 treated with radiotherapy alone (RT), 111 with radiotherapy plus hyperthermia (RT + HT). Only 56% of the 24 tumors less than 3 cm and 36% of the 53 lesions larger than 3 cm received what was felt to be "adequate" therapy (greater than or equal to 29 Gy and 8 heating sessions). Overall complete response (CR) was observed in 28% of the patients treated with RT, and 32% of the patients receiving RT and heat. Response has been found in previous analyses of this and other RTOG studies to be significantly related to both maximum tumor diameter (less than 3 or greater than or equal to 3 cm) and site/histology (breast/adenocarcinoma, head and neck/squamous, or other site/histologies). In the head and neck tumors less than 3 cm in diameter there was no difference in CR with irradiation alone or combined with hyperthermia (46% vs 43%). However, in the breast, and trunk and extremities a better CR rate was noted with irradiation and heat (55% and 67%) than with irradiation alone (33% and 0). In lesions less than 3 cm treated with irradiation and heat the probability of remaining in response was 80% compared with 15% with irradiation alone. In lesions larger than 3 cm no difference in CR was observed in either treatment group. It has been hypothesized that the response rate is higher in patients with smaller lesions (less than 3 cm) and in breast/chest wall, trunk/extremity lesions because these tumors and anatomical sites are easier to heat adequately. Problems encountered in correlating tumor response with quality of heating include less than optimal heating in larger lesions and the limited ability of current thermometry to accurately represent the temperature distribution in a tumor. Furthermore, differences in equipment and treatment practices among institutions add to the variability in heat administration data collected. In addition, tumor response may be difficult to judge because of short survival of some patients and occasionally rapid tumor regression that may cause necrosis which may be misinterpreted as persistent tumor.(ABSTRACT TRUNCATED AT 400 WORDS)

The current and potential role of hyperthermia in radiotherapy

Current clinical experience strongly suggests that hyperthermia will become an important modality as an adjuvant to radiotherapy in the treatment of locally advanced solid tumors. Hyperthermia must therefore be considered a topic of general interest. Biologically, hyperthermia has two different types of interactions with radiation. Firstly, heat has a radiosensitizing effect. This is most prominent with simultaneous application, but is of the same magnitude in both tumor and normal tissue and will not improve the therapeutic ratio unless the tumor is heated to a higher temperature than the normal tissue. Secondly, hyperthermia exhibits a direct cytotoxic effect, and a moderate heat treatment alone can almost selectively destroy tumor cells in a nutritionally deprived chronically hypoxic and acidic environment. Because such cells are the most radioresistant, a smaller radiation dose is needed to control the remaining more radiosensitive cells. If critical, irradiated normal tissues are also heated, the cytotoxicity is best utilised if heat is given at least 3-4 hours after irradiation. The magnitude of both the sensitizing and the cytotoxic effect depends on temperature and heating time. Clinically, heating of superficial tumors (e.g. breast, neck nodes and malignant melanoma) has confirmed the biological rationale for using hyperthermia as an adjuvant to radiotherapy. An overview of available data gives thermal enhancement ratios of approximately 1.5 in several superficial tumor sites after external heating. From a practical point of view, true simultaneous treatment is almost impossible using external heating, and the major effect of the combined treatment will have to rely on hyperthermic cytotoxicity. This makes the design of clinical schedules less complicated since only a few heat fractions may be needed to achieve an optimal effect. On this basis, several randomized clinical trials have been activated with the aim to evaluate the role of adjuvant hyperthermia in the primary treatment of advanced (superficial) tumors. In addition, studies are underway to specifically elucidate the clinical relevance of thermotolerance and other biological issues. So far, the clinical evaluation has almost solely been limited to superficial tumors, or to situations where interstitial heating is feasible. External heating of "deep" seated tumors is still preliminary, and most studies are in Phase I-II, with emphasis on toxicity and feasibility. The initial results are promising with regard to improved tumor control and acceptable toxicity.

Low dose reirradiation in combination with hyperthermia: a palliative treatment for patients with breast cancer recurring in previously irradiated areas

Ninety-seven patients with breast cancer recurring in a previously irradiated area (mean dose 44 Gy) were reirradiated in combination with hyperthermia and had evaluable tumor responses. In the reirradiation series, radiotherapy was given twice weekly in most patients, with a fraction size varying from 200 to 400 cGy, the total dose varying from 8 to 32 Gy. Hyperthermia was given following the radiotherapy fractions. The combined treatment resulted in 35% complete and 55% partial responses. Duration of response was median 4 months for partial response and 26 months for complete response, respectively. The median survival time for all patients was 12 months. Acute skin reaction was mild, with more than moderate erythema in only 14/97 patients. Thermal burns occurred in 44/97 patients, generally at sites where pain sensation was decreased, and therefore they did not cause much inconvenience. In the 19 patients who survived more than 2 years, no late radiation damage was observed. When patients who received a "high dose" (greater than 29 Gy and hyperthermia) were compared with those who received a "low dose" (less than 29 Gy and hyperthermia), a higher complete response rate was observed in the high dose group (58% vs. 24%), whereas no difference in acute toxicity was found. We conclude that reirradiation with 8 x 4 Gy in combination with hyperthermia twice weekly is a safe, effective and well tolerated method for palliative treatment of patients with breast cancer recurring in previously irradiated areas.

Hyperthermia improves local tumour control in locally advanced breast cancer

We report three patients with advanced breast cancer who received hyperthermia (43 degrees C over 1 h, weekly x 4) and radiotherapy as palliative treatment for chest-wall recurrence. The case reports demonstrate situations where hyperthermia may be beneficial. These include tumours where radiotherapy alone is not expected to achieve control, such as large fungating tumours, and in previously irradiated areas. In these patients, hyperthermia with radiation achieves better local control of the tumour and delays the need for systemic chemotherapy. This may improve the quality of palliation.

Stanford University institutional report. Phase I evaluation of equipment for hyperthermia treatment of cancer

From September 16, 1981, through April 4, 1986, a total of 21 radiative electromagnetic (microwave and radiofrequency), ultrasound and interstitial radio-frequency hyperthermia applicators and three types of thermometry systems underwent extensive phantom and clinical testing at Stanford University. A total of 996 treatment sessions involving 268 separate treatment fields in 131 patients was performed. Thermal profiles were obtained in 847 of these treatment sessions by multipoint and/or mapping techniques involving mechanical translation. The ability of these devices to heat superficial, eccentrically located and deep-seated tumours at the major anatomical locations is evaluated and the temperature distributions, acute and subacute toxicities, and chronic complications compared. Average measured tumour temperatures between 42 degrees C and 43 degrees C were obtained with many of the devices used for superficial heating; average tumour temperatures of 39.6 degrees C to 42.1 degrees C were achieved with the three deep-heating devices. When compared to the goal of obtaining minimum tumour temperatures of 43.0 degrees C, all devices performed poorly. Only 14 per cent (118/847) of treatments with measured thermal profiles achieved minimum intratumoural temperatures of 41 degrees C. Fifty-six per cent of all treatments had associated acute toxicity; 14 per cent of all treatments necessitated power reduction resulting in maximum steady-state temperatures of less than 42.5 degrees C. Direct comparisons between two or more devices utilized to treat the same field were made in 67 instances, including 19 treatment fields in which two or more devices were compared at the same treatment session. The analyses from direct comparisons consistently showed that the static spiral and larger area scanning spiral applicators resulted in more favourable temperature distributions. Three fibreoptic thermometry systems (Luxtron single channel, four channel and eight channel multiple [four] probe array), the BSD Bowman thermistor system and a thermocouple system were evaluated with respect to accuracy, stability and artifacts. The clinical reliability, durability, and patient tolerance of the thermometry systems were investigated. The BSD Bowman and third generation Luxtron systems were found clinically useful, with the former meeting all of our established criteria.

Response of canine oral carcinomas to heat and radiation

Thermal enhancement of radiation response improved the probability for local tumor control without increasing the risk for late complications in this study of relatively advanced stage tumors. Thirty-eight dogs with naturally occurring oral carcinomas were randomized to two radiation dose response groups to receive radiation alone or combined with local hyperthermia. Radiation was delivered in 10 fractions over 22 days. Heating was done 3 hours after seven of the radiation doses. The objective was to maintain a minimum tumor temperature of 42 degrees C and a maximum normal tissue temperature of 40 degrees C for 30 minutes. Normal tissue temperatures were usually 40 degrees C or less but there was great heterogeneity in tumor temperatures. Temperatures at tumor margins never exceeded 41.5 degrees C. The TCD50 for radiation was 38 Gy (32-46 Gy, 95% C.I.) and for radiation and heat it was 33 Gy (30-36 Gy, 95% C.I.). The slope of the dose response was much steeper for radiation and heat than for radiation alone indicating that the heterogeneity of tumor response was decreased with heat. All tumors were controlled at 40 and 45 Gy with heat whereas only 57% and 75% were controlled with 40 and 45 Gy radiation only. There were no late necroses for radiation and heat. The tumor control enhancement might be improved with different sequences, number of heatings or other time temperature relationships. It is not possible to predict the optimum treatment scheme because of the lack of knowledge of the influence of hyperthermia on subsequent heat or radiation treatments. That influence could be affected greatly by changes in tumor microcirculation, pH, and oxygenation as well as development and decay of thermotolerance in tumor and normal tissue.

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.

Clinical application of thermal isoeffect dose

Clinically, there is strong rationale for developing a method which will provide a scientific basis for comparing the efficacy of one hyperthermia treatment with another. In order to accomplish this goal, methods must first be developed which will allow the clinician to know the three-dimensional temperature distribution in heated tissue. In this paper, examples of how this goal can be achieved are presented. Techniques for compensating for various modifiers of hyperthermia effectiveness are proposed. The limitations and advantages of these approaches are described and directions for future research are discussed.

The use of implanted closed-tip catheters for the introduction of thermometry probes during local hyperthermia treatment series

In the past two and a half years custom-made closed-tip catheters have been used to allow extensive temperature monitoring with multi-junction thermocouple probes during local hyperthermia. Data from animal experiments indicate that the use of thermometry probes within such a catheter provides reliable temperature measurements. In order to reduce stress to the patient the catheters were fixed so that they could stay in place during the total treatment series. The catheters, outer diameter 1.22 mm, were introduced through hollow needles under sterile conditions before the first hyperthermia session, and fixed using Histo-acryl (tissue adhesive) and Tegaderm (transparent adhesive). Recently, the data concerning the first 180 catheters placed in 74 treatment areas were evaluated. In one patient, an abscess developed 10 days after removal of the (3) catheters, which required surgical intervention, but it was not clear whether these problems had developed as a result of catheter placement. There were no problems with 139 of the remaining 177 catheters (79 per cent) and in 50 treatment fields (68 per cent), respectively, for a duration of 9-55 (mean 23) days. Ten catheters (6 per cent) were lost during the treatment series after 1-22 (mean 10) days. With 28 catheters (16 per cent) infection was observed, 14-27 (mean 19) days after insertion, which necessitated catheter removal before the last treatment session in 11 cases (6 per cent). The complication rate decreased with increasing experience; from 29 per cent (25/85) in the early period to 14 per cent (13/92) in the later period. We conclude that the use of closed-tip catheters under proper control generally causes few, if any, problems. This results in the acquisition of a substantial amount of reliable temperature data at reproducible sites, and it is well tolerated by the patient.

Retrospective analysis of the response of tumours in patients treated with a combination of radiotherapy and hyperthermia

One hundred and twelve patients with various carcinomas were treated on 112 fields with radiotherapy and hyperthermia, using non-invasive techniques. Radiotherapy dose ranged from 13-70 Gy (except for one patient receiving hyperthermia alone) with a mean of 28.6 Gy. The combined treatment was primarily aimed at giving palliation; 79 per cent of the patients had received previous irradiation on the same area. Hyperthermia was given twice weekly following radiotherapy. From the temperature data collected, 12 different parameters expressing the hyperthermia 'dose' were derived. The various parameters for both treatment modalities, i.e. radiotherapy and hyperthermia, and some of the tumour parameters were statistically evaluated with respect to their influence on tumour response. The overall response rate was 87 per cent including 33 per cent complete response. The complete response rate increased with increasing radiotherapy total dose, i.e. from 23 per cent (14-25 Gy) and 38 per cent (28-36 Gy) to 60 per cent (greater than 38 Gy). A positive correlation between the tumour temperature parameter representative of the coldest spot in the tumour, and the level of response was found. Achievement of complete response appeared also to be determined to a considerable extent by radiotherapy total dose as well as tumour volume. The correlation between response level and the minimum hyperthermia dose parameters persisted, however, after correction for the influence of tumour volume and radiotherapy total dose. These results support the opinion that higher tumour response rates can be achieved by increasing the hyperthermia treatment level at the coldest spot in the tumour.

Combined treatment with radiation and hyperthermia in metastatic malignant melanoma

In 24 patients with metastatic malignant melanoma, combined treatment with radiation and hyperthermia was administered to 38 localizations, radiation alone to 8 comparative localizations and hyperthermia alone to 3 localizations. Hyperthermia was administered during one hour by using a 433 MHz microwave generator. The heat treatment was given within 30 min following irradiation. Although an intratumoral temperature of 43 degrees C was aimed, considerable variations occurred during one session and from session-to-session. Radiation schedules consisted in either one large fraction (6-8 Gy) once a week in 14-21 days or two fractions (4-5 Gy) twice a week in 21 days. In the group of patients receiving irradiation once a week, three heat treatments were administered. In the twice-a-week radiation schedule, six heat sessions were given. The overall complete response (CR) rate in patients receiving combined treatment was 50%. In the group of patients treated with hyperthermia and irradiation schedules of 8 Gy per fraction, the CR rate was 83%. Irradiation alone achieved 38% CR rate but some of these CR relapsed during follow-up whereas the comparative area treated with radiation and heat remained under control at this time. The lesions treated with heat alone did not show any response to treatment. Enhancement of the acute skin reactions was generally observed. However, because the total doses were relatively low, this enhancement did not constitute a clinical problem. CR appears to occur more frequently in small tumor sizes. The highest and lowest temperature ever registered during any session of hyperthermia did not seem to correlate with the tumor response.

Estimation of therapeutic gain in clinical trials involving hyperthermia and radiotherapy

It is clear from discussions in this paper that phase III testing of hyperthermia in human patients must proceed in a cautious and stepwise fashion. Because of the risks of increasing late effects, either due to direct thermal damage or thermo-radiosensitization of normal tissues, it is not prudent to proceed with such testing in sites where there is a risk of excessive normal tissue heating. The correlations between temperature and prognosis in heated tumours implies that sites and techniques should be chosen where the chance of achieving relatively uniform heating are maximized. Methods of quality assurance are of equal importance and need to be carefully designed. Even then, retrospective analyses with temperature variations used as prognostic covariates are essential. Other factors, such as tumour volume and radiotherapy dose should be carefully controlled in experimental and control groups. Finally, protocol compliance is a real problem which will cause problems in interpretation of results, especially in studies designed to look at hyperthermic time-dose fractionation.