Studies relevant to a means of quantifying the effects of hyperthermia

First prize: direct real-time temperature monitoring for laparoscopic and CT-guided radiofrequency ablation of renal tumors between 3 and 5 cm

PURPOSE

To evaluate our experience with radiofrequency ablation (RFA) of renal tumors in the range of 3 to 5 cm.

PATIENTS AND METHODS

A series of 96 patients underwent 104 tumor laparoscopic or percutaneous CT-guided RFAs. We identified 37 tumors between 3 and 5 cm at the time of the ablation. Non-conducting temperature probes, independent of the radiofrequency (RF) electrode, were placed at the peripheral and deep margins of the tumor in order to achieve real-time temperature monitoring of the ablation zone. All ablations were continued until the peripheral and deep temperature probes reached 60 degrees C.

RESULTS

All 37 patients (100%) achieved complete necrosis at the initial session. There were two radiographic failures at 9 months and 30 months that required a second treatment (95% radiographic success rate). Tissue samples taken at the time of the re-treatment (one partial nephrectomy with numerous biopsies of the deep and peripheral margins and one repeat ablation with eight core biopsies) showed no evidence of viable tumor with hematoxylin and eosin or nicotinamide adenine dinucleotide viability stains. The average length of follow-up was 11.3 months (range 1-44 months). No patient with localized disease at the time of the RFA developed local extension or metastatic disease in follow-up.

CONCLUSIONS

The majority of renal tumors between 3 and 5 cm can be ablated with complete necrosis in a single session. Placement of independent temperature probes at the peripheral and deep margins of the tumor provides real-time monitoring that assists in the deployments of the RF electrode and determining the appropriate duration of the ablation cycles. Attention to real-time thermometry decreases the need for repeat sessions to achieve complete necrosis for larger tumors. Likewise, real-time thermometry decreases the incidence of overtreatment of normal parenchyma and prevents collateral damage to adjacent vital structures (ureter, pancreas, bowel, spleen, nerves) outside the desired zone of ablation.

Radiofrequency Interstitial Tissue Ablation: Wet Electrode

Minimally invasive methods for destroying tissue have been investigated for more than a decade, and growing interest has emerged in small probe or needle ablative techniques. Many energy sources that freeze or heat tissue have been studied. This paper discusses radiofrequency (RF) thermal therapy as delivered by the saline-augmented ("wet" or virtual) electrode. The technique modifies the electric field distribution and the resultant heat deposition within tissues by interstitially infusing a highly conductive electrolyte solution during the application of RF energy. We consider the mechanism of action of the saline-augmented probe, with emphasis on tissue electrical impedance, temperature distributions, and how the fluid circumvents the limitations of standard "dry" probes. If optimized for the particular application, the wet electrode can produce small to large ablation volumes quickly and controllably with a single needle stick. Because there is no desiccation or extremely high temperature, the tissue is not subjected to a phase shift of carbonization, which may reduce post-treatment inflammation and improve healing. The liquid RF electrode will find applications in the interstitial treatment of various tissues, including tumors.

Quantifying tissue damage due to focused ultrasound heating observed by MRI

Focused ultrasound heating of ex vivo bovine kidney and liver was monitored using magnetic resonance imaging (MRI) to investigate the quantitative relationship between time-dependent temperature elevations and altered contrast in MR images due to thermal coagulation. Proton resonance frequency shift MR thermometry was performed during heating at 10 sec intervals (single-slice fast spoiled GRASS [FSPGR], theta/TE/TR 30 degrees/11/39 msec, field of view 8 cm, 256 x 256, 3 mm slice thickness, 1 NEX); post-heating MR images were T1-weighted (3D-FSPGR, theta/TE/TR 60 degrees/25/200 msec, 1 mm slice thickness, 3 NEX). Analysis of the resulting temperature versus time data using the Arrhenius relationship and a simple binary discrimination model showed that thermal coagulation occurred with heating at approximately 54 degrees C for 10 sec in both tissues and could be predicted with approximately 625 microm spatial resolution. These results suggest that quantitative MR guidance of thermal coagulation therapy is feasible, and they provide information useful for designing future investigations in vivo.

Sensitivity of hyperthermia trial outcomes to temperature and time: implications for thermal goals of treatment

PURPOSE

In previous work we have found that the cumulative minutes of treatment for which 90% of measured intratumoral temperatures (T90) exceeded 39.5 degrees C was highly associated with complete response of superficial tumors. Similarly, the cumulative time for which 50% of intratumoral temperatures (T50) exceeded 41.5 degrees C was highly associated with the presence of > 80% necrosis in soft tissue sarcomas resected after radiotherapy and hyperthermia. In the present work we have calculated the time for isoeffective treatments with T90 = 43 degrees C and T50 = 43 degrees C, respectively, using published thermal isoeffective dose formulae. The purpose of these calculations was to determine the sensitivity of treatment outcome to variations in thermal isoeffective dose.

METHODS AND MATERIALS

The basis for the calculations were the thermal parameters and treatment outcomes in three patient populations: 44 patients with moderate or high grade soft tissue sarcoma treated preoperatively with hyperthermia and radiation; 105 patients with superficial tumors treated with hyperthermia and radiation, and 59 patients with deep tumors treated with hyperthermia and radiation.

RESULTS

The thermal dose values calculated are strongly associated with outcome in multivariate logistic regression analysis. Simple dose-response equations result from the analysis, and we use these equations to assess the sensitivity of outcome upon variations in thermal dose. This information, in turn, allows us to estimate the number of patients required in Phase II and III trials of hyperthermia and radiation therapy.

CONCLUSIONS

For regimens of 5 to 10 hyperthermia treatments, improvements in median T90 (superficial tumors) and T50 (deep tumors) parameters by 1.2-1.5 degrees C could result in response rates high enough (compared to radiotherapy alone) to justify Phase III trials. A similar improvement in response rates would require an increase in overall duration of treatment by a factor of 3 to 5. This would be difficult to achieve while also avoiding thermal tolerance induction. Achieving these temperature goals may be possible with improvements in hyperthermia technology. Alternatively, there may be ways to increase the sensitivity of cells to temperatures that can be achieved currently, such as pH reduction or chemosensitization.

Hyperthermia in cancer growth regulation

With present techniques, hyperthermia used alone can cause complete clinical regression in 10-15% of tumours but the duration of response is very short. The greatest advantage for hyperthermia at the present time appears to be in combination with radiation in the local control of cancer growth. Currently, large randomised phase III studies are in progress to determine whether the addition of local hyperthermia to radiation or chemotherapy yields significant advantage. Phase III studies of wholebody hyperthermia in combination with chemotherapy are planned for the future and will include tumours with a high growth fraction such as small cell lung cancer and high grade non Hodgkins lymphoma.

Relationships among tumor temperature, treatment time, and histopathological outcome using preoperative hyperthermia with radiation in soft tissue sarcomas

The lack of an unambiguous thermal dosimetry continues to impede progress in clinical hyperthermia. In an attempt to define better this dosimetry, a model based on the cumulative minutes during which arbitrary percentages of measured tumor temperature points exceeded an index temperature was tested in patients with soft tissue sarcomas treated with preoperative hyperthermia and conventional radiation therapy. Patients received 5000-5040 cGy at 180-200 cGy per fraction. Hyperthermia was delivered 30-60 minutes after radiation therapy and given for 60 minutes. Patients were randomized between one and two hyperthermia treatments per week for a total of five or 10 treatments, respectively. Lesions were excised 4-6 weeks after completion of hyperthermia/radiation therapy. Successful treatment outcome was considered to be the finding of greater than 80% necrosis of the sarcoma upon histopathologic examination of the resected specimen. Forty-five patients were eligible with thermometry data available in 44 patients. An average of 19 interstitial sites were monitored each treatment per tumor. Sixty percent of tumors had a successful histopathologic outcome. Univariate analysis demonstrated that several descriptors of the temperature distribution were strongly related to treatment outcome; more strongly than nonthermometric factors, such as the number of treatments per week, tumor volume and patient age and more strongly than the commonly used temperature descriptors Tmin and Tmax. Descriptors that incorporated both temperature and time were also superior to the more commonly used descriptors Tmin and Tmax. Multivariate stepwise logistic regression analysis revealed that a descriptor of both the hyperthermia treatment time and the frequency distribution of intratumoral temperatures was the strongest predictor of histopathologic outcome and that the best predictive model combined this time/temperature descriptor and one versus two treatment per week grouping. The more conventional temperature descriptor, minimum measured tumor temperature, did not significantly enhance the predictive power of treatment group. Based on these results, we recommend that descriptors based on both the frequency distribution of intratumoral temperatures and hyperthermia treatment time be tested for relationships with treatment outcome in other clinical data bases. Furthermore, we recommend that temperature descriptors that are less sensitive to catheter placement and tumor boundary identification than Tmin and Tmax (such as T90, T50, and T10) be tested prospectively along with other important thermal variables in Phase II trials in further efforts to define a thermal dosimetry for spatially nonuniform temperature distributions.

Time-temperature analysis of cell killing of BHK cells heated at temperatures in the range of 43.5 degrees C to 57.0 degrees C

Baby hamster kidney (BHK) cells were heated at temperatures in the range of 43.5 degrees C to 57.0 degrees C to determine the time-temperature relationship of cell killing. The cells were grown on 0.025 mm thick pieces of mylar to minimize warm-up times. After heating, the cells were plated for the colony formation assay. The endpoints of 1%, 10%, or 90% isosurvival, or the D0 values of the survival curves were used to construct plots of the logarithm of the reciprocol of the exposure time versus the reciprocol of the absolute temperature. The data for each endpoint resulted in a straight line plot, indicating that the time-temperature relationship for cell killing remained constant from 43.5 degrees C to 57.0 degrees C; namely, a 1.8-fold increase in exposure time was required for a 1 degree C decrease in temperature in order to obtain isosurvival. Heated BHK cells were also examined using electron microscopy. The threshold level of altered morphology was the dissociation of polyribosomal structure and the formation of electron-dense granules within the mitochondria. The time-temperature relationship for the induction of this altered morphology was identical to that for the 90% isosurvival endpoint. Hence, the appearance of altered morphology appears to be related to cell killing.

Regional hyperthermia for advanced tumors: a clinical study of 353 patients

A Phase I study using deep regional hyperthermia (HT) with an annular phased array was conducted in 14 U.S. medical centers from 1980 through 1986. There were 353 patients whose average age was 57 years. All patients had advanced recurrent or persistent tumors. Prior frequently complex, multimodality anti-cancer therapy was received by 71% of the patients. Gastrointestinal adenocarcinoma was present in 146 (41%) patients, genitourinary tumors in 86 (24%), soft tissue sarcomas in 46 (13%), malignant melanoma in 21 (6%) and 15% had other tumors. The sites treated included: pelvis 55%, abdomen 21%, liver 14%, thorax 6%, and other sites 3%. All patients received deep regional HT with an average frequency of 55 MHz. A total of 1412 HT treatments was administered to these 353 patients with an aim to increase the temperature in the volume of interest to greater than 42 degrees C for greater than or equal to 30 minutes. Thermal dose (TD in equivalent minutes at 42.5 degrees C) was less than 50 in 104 (29%), greater than or equal to 50 less than 100 in 30 (11%), greater than or equal to 100 in 26 (7%), and greater than 200 in 34 (10%). The remaining 150 (42%) patients had TD = 0. In addition to HT, 260 (74%) received radiotherapy (RT). RT was given at 180 or 200 cGy daily with an average total dose of 33.4 Gy. A total of 42 (12%) patients were given chemotherapy (CT) with HT, and 15 (4%) CT + HT + RT/HT alone was given to 47 (13%) patients. Complete response (CR) was obtained in 35 (10%) and partial response (PR) in 59 (17%) patients. CR was 12% in patients who received RT, vs 2% in those who did not receive it, p = 0.003. Radiation dose was an important factor influencing response, p less than 0.001. Thermal dose was not an important parameter influencing tumor response. A duration of CR ranged from 4 to 73 weeks with an average duration of 31 weeks and the median duration of 28 weeks. The overall 2-year survival was 13% with the median survival of 42 weeks. Patients with CR and PR had a 2 year survival of 41%, and a median survival of 71 weeks. This compared with 8% 2-year survival and 24 weeks median survival in patients who did not have CR or PR, p less than 0.001. Of the patients presenting with significant pain, 62% had complete or partial pain relief.(ABSTRACT TRUNCATED AT 400 WORDS)

Hyperthermia quality assurance guidelines

These Hyperthermia Quality Assurance guidelines are a result of a joint workshop of the Hyperthermia Committee of the American College of Radiology and the Hyperthermia Physics Center, which is the national quality assurance program under Contract No. N01-CM-37512 with the National Cancer Institute. Hyperthermia technology presently lacks the kind of standardization in equipment, treatment procedures, patient monitoring, and treatment documentation available in radiotherapy. Therefore, preventing unacceptable variability in treatment data demands a strong commitment to in-house quality control procedures and to centralized quality assurance reviews in cooperative multi-institutional trials. This paper presents a set of test procedures necessary to ensure proper operation of equipment, suggests a frequency for such tests, and also includes guidelines on quality control procedures to be used during treatment to improve the safety, effectiveness, and reproducibility of hyperthermia treatments. A set of forms are presented to indicate the minimum data, albeit incomplete, that must be collected for acceptable documentation of treatment. These guidelines should be valuable not only to the new entrants in the field but also to those participating in multi-institutional cooperative hyperthermia trials. They have been approved by the Hyperthermia Committees of American College of Radiology, American Society for Therapeutic Radiology and Oncology, Radiation Therapy Oncology Group and the American Association of Physicists in Medicine.

Whole body hyperthermia in dogs using a radiant heating device: effect of surface cooling on temperature uniformity

Rectal and subcutaneous temperatures were measured during a total of 10 whole body hyperthermia treatments conducted in six dogs. During five of the treatments skin cooling, by means of initiating air flow through the radiant heating device, was necessary during the plateau phase because rectal temperature exceeded the target value. Skin cooling was not necessary in the other five treatments. Although the rectal temperatures were similar in all 10 treatments, extensive and rapid subcutaneous temperature non-uniformity, of approximately 4 degrees C, developed during treatments where skin cooling was necessary. During the treatments where skin cooling was not necessary, the subcutaneous temperature remained approximately equal to the rectal temperature. These data indicate that the environment in the radiant heating device during the plateau phase can have a profound effect on the temperature at superficial sites, which is not reflected by the temperature measured at deeper sites. The temperature at superficial sites should be measured during whole body hyperthermia to assure that the prescribed heat dose is administered to the largest percentage of body mass possible. Active skin cooling during whole body hyperthermia should be avoided if possible.

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.

1985 Douglas Lea memorial lecture. Hyperthermia in the treatment of cancer

There are sound biological reasons for using hyperthermia in the treatment of malignant disease. This review includes a discussion of this rationale and describes effects of hyperthermia either given alone or in combination with ionising radiation to cells in vitro, tumours or normal tissues. Topics discussed include thermotolerance, step-down sensitisation, fractionation, re-treatment of previously irradiated sites, thermal enhancement ratio and thermal dose. Problems of heat delivery and temperature measurement are considered and the current status of clinical studies is stated briefly.