Radiotherapy and hyperthermia. Analysis of clinical results and identification of prognostic variables

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)

Tumor temperature distributions predict hyperthermia effect

Review of clinical hyperthermia (HT) trial results shows that there previously has not been a robust model relating efficacy of HT treatments to characteristics of the temperature distribution. Lack of a model has been an impediment in Phase II trials; these trials must include defining the prescription for HT treatment, optimizing the schedule of HT treatments, and defining quality assurance procedures. We propose a model that is based upon noting that the majority of a tumor volume is contained in the outermost "shell" of a solid tumor, across which shell the radial temperature distribution is assumed to be linear. Any linear distribution can be defined by coordinates of a point and a slope, and we choose the temperature at the radiographically defined edge of a tumor and the slope (dT/dr) across the outer shell as these determinants of the linear radial temperature distribution. A discriminant analysis of success or failure of treatment can then be based upon these two descriptors (Tedge, dT/dr). We have tested this model using data from patients with soft tissue sarcoma (Stage IIB or greater) that have entered an ongoing prospective trial of conventional preoperative radiotherapy (5000 cGy/25 Fx/5 wk) together with HT, the latter randomized to be given once or twice weekly during the 5 week course. Wide local excision of the primary tumor is done 1 month after completion of radiotherapy, and the extent of histologic change in the resected specimen is scored. Our model has an 86% predictive value for lack of complete or nearly complete necrosis in the resected specimen according to whether the time-averaged Tedge and slope during each HT treatment satisfy the equation Tedge + 1.2 (slope in degree C/cm) less than or equal to 40.6 degrees C in all but one treatment at most. Conversely, in 85% of cases with complete or nearly complete tumor necrosis, temperature distributions satisfied Tedge + 1.2 (slope in degree C/cm) greater than 40.6 degrees C during at least one HT treatment. Requiring greater than or equal to one third of treatments of a patient to satisfy the preceeding discriminant equation resulted in 80% of patients being correctly classified as a responder or nonresponder, with only one false positive prediction (patient incorrectly classified as a responder). The model can reveal systematic changes in the edge temperature distribution during the treatment course that are consistent with tumor perfusion changes inferred and measured by independent means.(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.

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.

Radical radiation alone versus radical radiation plus microwave hyperthermia for N3 (TNM-UICC) neck nodes: a prospective randomized clinical trial

Between September 1985 and December 1986, 44 N3 (TNM-UICC) metastatic squamous cell cervical lymph-nodes were randomized to receive conventionally fractionated radical irradiation (RT) to a total dose of 64-70 Gy, or conventionally fractionated radical irradiation plus twice a week local microwave hyperthermia (Ht). The two major end points of this study were (a) local control rates evaluated at 3 months after the end of combined therapy and (b) incidence of acute local toxicity. Thirty-six nodes (82%) were evaluable as of December 1986, at which time there was a premature closure of this study due to ethical reasons. An interim analysis had revealed a statistically significant difference in complete response rates in favor of the combined arm (p = 0.0152). The complete response rates were 82.3% (14/17) for the combined treatment arm versus 36.8% (7/19) for the control irradiation arm, leading to an iso-dose thermal enhancement ratio (TER) value of 2.23. Both arms are comparable in average total RT dose delivered (RT: 67.05 Gy; RT + Ht: 67.85 Gy) and in average maximum node diameter (RT arm: 4.81 cm; RT + Ht: 4.88 cm). Acute local toxicities were similar in irradiated and heated plus irradiated neck regions; only one skin burn was observed. As possible treatment related death, one patient in the RT + Ht arm died 2 months after completion of therapy with a carotid rupture associated with extensive tumor necrosis. These results confirm previous non-randomized reports suggesting that hyperthermia in combination with full dose conventionally fractionated irradiation significantly enhances the chance of early local control of fixed N3 neck nodes without exhibiting an increase of acute local toxicity.

Intraoperative radiotherapy for patients with carcinoma of the pancreas. The Howard University Hospital experience, 1978-1986

During the period from 1978 to 1986, 106 patients were diagnosed with carcinoma of the pancreas; 30 of these patients were excluded from this study. Of the remaining 76 patients, 40 did not receive intraoperative radiotherapy (IORT) and were used as the nonrandomized control group for the 36 patients who did receive IORT after histologic confirmation of carcinoma of the pancreas. The records of 35 patients were available for review. The group receiving IORT ranged in ages from 43 to 89 years (20 males and 15 females). Seventeen patients had distant metastatic disease. The primary was located in the head of the pancreas in 32 and the body in three. No patient in this group had a curative resection. All patients were treated by a combination of biliary and gastric bypass prior to or concurrent with IORT. IORT was begun only after obtaining a histologic diagnosis and prior to the completion of any anastomosis. Necrotizing pancreatitis occurred in the treated group. There was no statistically significant difference in the survival of the nonrandomized control and treated groups.