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

Hyperthermia enhances tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human cancer cells

PURPOSE

This study investigated whether hyperthermia can enhance TRAIL-induced apoptotic death.

METHODS

Human prostate adenocarcinoma DU-145, human pancreatic carcinoma MIA PaCa-2 and BxPC-3, human colon fibroblast CCD-33Co and rat prostate endothelial YPEN-1 cells were treated with various concentrations of TRAIL (0-200 ngml(-1)) with hyperthermia (40-42 degrees C).

RESULTS

It was observed in human cancer cells, but not in normal cells, that TRAIL induced apoptotic death and also that hyperthermia (40-42 degrees C) promoted TRAIL-induced apoptotic death. Enhancement of TRAIL-mediated apoptosis by hyperthermia was detected by an increase in PARP cleavage, the hallmark feature of apoptosis, as well as by activation of caspases. There were no significant changes in the intra-cellular levels of death receptors (DRs), decoy receptors (DcRs) and anti-apoptotic proteins. Interestingly, data from in vitro enzyme kinetics assay demonstrated that hyperthermia promoted caspase enzyme activity.

CONCLUSIONS

These data suggest that cancer cells are more susceptible to TRAIL in the condition of hyperthermia (40-42 degrees C). The promotion of caspase enzyme activity by hyperthermia may be responsible for enhancement of TRAIL-induced apoptotic death.

The impact of ultrasonic parameters on chest wall hyperthermia

A transient, three-dimensional acousto-thermal numerical model for chest wall anatomies was developed to evaluate the impact of ultrasonic parameters on thermal coverage. The following independent variables were considered: (1) the relative output intensities of the low and high frequency components of an unfocused dual-frequency ultrasonic beam (xi1); (2) the depths of the soft-tissue bone (d(b)) and soft-tissue-lung (d(u)) interfaces; (3) the intensity reflectivities of these interfaces; and (4) the intensity attenuation coefficient of bone. Several important results were obtained. First, acoustic reflections from the underlying bone and lung surfaces may contribute significantly to heating of the overlying soft-tissue. Secondly, a strong dependence of optimal xi1 values on d(b) and d(u) values was found. Chest wall volumes with 2-3 cm of soft-tissue overlying the ribs were optimal targets for unfocused ultrasound hyperthermia. Thirdly, the maximum steady state temperature in bone also strongly depended on xi1. Finally, the largest difference between the maximum temperature in bone and the maximum temperature in soft-tissue during initial transient heating was between -1.4 degrees C and 0.8 degrees C. That is, the maximum temperature in the field, either during the transient period or at steady state, did not always occur in bone. It is concluded that control of power deposition penetrability offers great potential for improving hyperthermia to chest wall targets in real time.

Ultrasound power deposition model for the chest wall

An ultrasound power deposition model for the chest wall was developed based on secondary-source and plane-wave theories. The anatomic model consisted of a muscle-ribs-lung volume, accounted for wave reflection and refraction at muscle-rib and muscle-lung interfaces, and computed power deposition due to the propagation of both reflected and transmitted waves. Lung tissue was assumed to be air-equivalent. The parts of the theory and numerical program dealing with reflection were experimentally evaluated by comparing simulations with acoustic field measurements using several pertinent reflecting materials. Satisfactory agreement was found. A series of simulations were performed to study the influence of angle of incidence of the beam, frequency, and thickness of muscle tissue overlying the ribs on power deposition distributions that may be expected during superficial ultrasound (US) hyperthermia of chest wall recurrences. Both reflection at major interfaces and attenuation in bone were the determining factors affecting power deposition, the dominance of one vs. the other depending on the angle of incidence of the beam. Sufficient energy is reflected by these interfaces to suggest that improvements in thermal doses to overlying tissues are possible with adequate manipulation of the sound field (advances in ultrasonic heating devices) and prospective treatment planning.

Use of whole body hyperthermia as a method to heat inaccessible tumours uniformly: a phase III trial in canine brain masses

In this study, whole body hyperthermia (WBH) was assessed as a means of heating intracranial tumours uniformly. Twenty-five dogs received radiation therapy and 20 the combination of radiation and WBH. Total radiation dose was randomly assigned and was either 44, 48, 52, 56 or 60 Gy. Because of WBH toxicity, intercurrent disease or tumour progression, seven of the 45 dogs received less than the prescribed radiation dose. For WBH, the target rectal temperature was 42 degrees C for 2h and three treatments were planned. In five of the 20 dogs randomized to receive WBH, only one WBH treatment was given because of toxicity. WBH toxicity was severe in six dogs, and resulted in death or interruption in treatment. Most tumours did not undergo a complete response, making it impossible to differentiate tumour recurrence from brain necrosis as a cause of progressive neuropathy. Therefore, survival was the major study endpoint. There was no survival difference between groups. One-year survival probability (95% CI) for dogs receiving radiation therapy alone was 0.44 (0.25, 0.63) versus 0.40 (0.19, 0.63) for dogs receiving radiation and WBH. There was no difference in the incidence of brain necrosis in the two treatment groups. Results suggest that use of WBH alone to increase the temperature of intracranial tumours as a means to improve radiation therapy outcome is not a successful strategy.

Simultaneous superficial hyperthermia and external radiotherapy: report of thermal dosimetry and tolerance to treatment

BACKGROUND

In vitro and animal studies indicate that a moderate temperature of 41 degrees C maintained for approximately 1 h will provide radiosensitization if radiation (RT) and hyperthermia (HT) are delivered simultaneously, but not with sequential treatment. A minimum tumour temperature of 41 degrees C is a more feasible goal than the goal of >42 degrees C needed for sequential treatment.

METHODS AND MATERIALS

Forty-four patients with 47 recurrent superficial cancers received simultaneous external beam radiotherapy and superficial hyperthermia on successive IRB approved phase I/II studies. All lesions had failed previous therapy, 35 were previously irradiated (mean dose 52.7 Gy). Hyperthermia was delivered with 915 MHz microwave or 1-3.5 MHz ultrasound using commercially available applicators. The average dimensions of 19 lesions treated with microwave were 4.7 x 3.6 x 1.7 cm and the average dimensions of 28 lesions treated with ultrasound were 8.0 x 6.1 x 2.9 cm. The most common sites were chest wall (15 cases) and head and neck (21 cases). Temperatures were monitored at an average of six intratumoral locations using multisensor probes. The median number of hyperthermia treatments was three and the median radiation dose 30 Gy. Radiation dose per fraction was 4 Gy with hyperthermia and 2 Gy or 4 Gy (depending on protocol) on non-hyperthermia days.

RESULTS

Six different measures of minimum monitored temperature and duration were found to be highly correlated with each other. There was nearly a one-to-one correspondence between minimum tumour time at or above 41 degrees C (Min t41) and minimum tumour Sapareto Dewey equivalent time at 42 degrees C (Min teq42). After four sessions 63% of cases had a per session average Sapareto Dewey equivalent time at 41 degrees C which exceeded 60 min in all monitored tumour locations. The complete and partial response rate in evaluable lesions were respectively 21/41 (51%) and 7/41 (17%) and were best correlated with site (chest wall showing best response). Toxicity consisted of 10/47 (21%) slow healing soft tissue ulcers which healed in all cases but required a median of 7 months. The most important predictors for chronic ulceration were cumulative radiation dose >80 Gy and complete response to treatment.

CONCLUSIONS

Minimum tumour temperatures maintained for durations compatible in vitro with thermal radiosensitization (if RT and HT are delivered simultaneously) are clinically feasible and tolerable for broad but superficial lesions amenable to externally applied ultrasound or microwave hyperthermia. The current in-house protocol is evaluating the impact of more than four hyperthermia sessions on the overall thermal dose distribution and toxicity.

HSP 70 induction and thermotolerance following interstitial hyperthermia in the dunning R3327 tumor in vivo

We investigated the use of an interstitial temperature self-regulating implant for fractionated hyperthermia delivery for treatment of prostatic disease. Nonuniform heating, lower temperatures between the implants, and lingering thermotolerance for additional hyperthermia treatments are concerns associated with the technique. Thermotolerance of the Dunning R3327 prostate adenocarcinoma to a 1 hour interstitial heating of 42-43°C has been estimated using inducible heat shock protein (HSP) 72 as an assay. The duration of thermotolerance in a nonuniformly heated tumor is necessary for optimization of multiple-treatment planning. HSP 72 expression is increased between 8 and 16 hours posttreatment. Growth curves for conditioned (treated once at 42-43°C minimum) tumors retreated at a minimum temperature of 45°C after 10 hours recovery (where elevated HSP 72 expression is evident) were compared with those retreated after 48 hours recovery (with normal HSP 72 expression) and with conditioned controls; both retreatment groups differed from controls (p < 0.0001). Growth curves for tumors with elevated HSP 72 expression after 10 hours differed from those retreated after 48 hours (p ≤ 0.0202). The results indicate that in vivo measurement of HSP 72 expression in the Dunning tumor is an adequate indicator of thermotolerance for optimal sequencing of hyperthermia fractions and that sufficiently high thermal doses are effective against thermotolerant cell populations.

A phase I and II clinical trial of a newly developed ultrasound hyperthermia system with an improved planar transducer

PURPOSE

The clinical usefulness of a newly developed ultrasound hyperthermia system was evaluated.

METHODS AND MATERIALS

The hyperthermia system uses a modified planer transducer operated at frequencies of 0.5, 1.0, and 1.5 MHz. The transducer has a nonvibrating part at the center to reduce the central hot spot. Frequency sweeping technique is also used to eliminate the annular hot spot around the center. Thirty-eight tumors in 29 patients were examined in this study. In 35 tumors, hyperthermia was given in conjunction with irradiation and/or chemotherapy, and in the remaining 3 tumors, hyperthermia alone was given. In all, a total of 153 hyperthermia sessions were performed.

RESULTS

The number of hyperthermia sessions per tumor ranged from 1 to 7 (mean, 4.0 +/- 1.3). The number of intratumor thermometry points per session ranged from 1 to 8 (mean, 4.3 +/- 1.5). The average intratumor temperature for tumors with a maximum depth of <3 cm, 3-6 cm, and >6 cm was 42.1 +/- 1.2, 41.7 +/- 1.4, and 39.9 +/- 2.0 degrees C, respectively. The percentage of monitored intratumor points with temperature exceeding 42 degrees C was 56 +/- 31%, 43 +/- 34%, and 21 +/- 24%, respectively. Of the 30 evaluable tumors treated with combined irradiation, 12 showed complete response, 14 partial response, and 4 no change. Observed complications included pain at the treatment site in 13 of the 153 treatment sessions and vesicle formation in 3 of the 38 treatment sites. No serious complication was seen.

CONCLUSIONS

These results indicate that the newly developed ultrasound hyperthermia system is clinically useful for the treatment of localized superficial and subsurface tumors with a maximum tumor depth of no more than 6 cm.

Thermal treatment parameters are most predictive of outcome in patients with single tumor nodules per treatment field in recurrent adenocarcinoma of the breast

PURPOSE

In previously reported studies using radiation therapy (XRT) and hyperthermia (HT) for treatment of superficial metastases from adenocarcinoma of the breast, we have identified several pretreatment and treatment parameters that correlated with rate of initial complete response (ICR) recorded at 3 weeks and duration of local control (DLC). These parameters include minimal intratumoral temperature, Tmin, and the temperature exceeded by 90% of the measured intratumoral temperatures, T90. Recently, others have shown that thermal dose defined as the cumulative time of isoeffective treatments with T90 = 43 degrees C (CUM EQ MIN T90 43) was predictive of complete response in superficial tumors. We have assessed the prognostic value of several formulations of this parameter for both ICR and DLC in a relatively uniform patient population treated with XRT-HT.

METHODS AND MATERIALS

The corresponding EQ MIN T90 43 were calculated for 332 HT treatments in 111 HT fields in 83 patients who started treatment between October 1982 and May 1992. Each field contained only one measurable superficially located nodular tumor recurrence or metastasis from adenocarcinoma of the breast that was treated with XRT-HT, had mapped or multiple point temperatures recorded, and had at least one posttreatment follow-up evaluation. The thermal doses from all treatments delivered to a field were added to obtain the total thermal dose, SUM EQ MIN T90 43. Logistic and life-table multivariate analyses were performed to determine which pretreatment parameters (including initial T-stage, prior XRT, and tumor volume at the time of HT) and treatment parameters (including XRT dose, Tmin, T90, thermal dose, and hormonal therapy) best correlated with ICR and DLC.

RESULTS

Of the treatment parameters tested, SUM EQ MIN T90 43 had the strongest correlation with both ICR (p = 0.0002) and DLC (p = 0.0014). Also, SUM EQ MIN T90 43 contributed to the best multivariate models predictive of ICR and DLC.

CONCLUSION

For this relatively uniform patient population, we have confirmed that SUM EQ MIN T90 43 is the treatment parameter most strongly correlated with not only response following XRT-HT, but also duration of local control. This formulation of thermal dose should permit prescriptions to be written for HT treatments. Prospective trials designed to confirm this thermal dose relationship are to be encouraged.

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.

Clinical results of thermoradiotherapy for soft tissue tumours

Thirty-one unresectable and/or recurrent soft tissue tumours in 27 patients underwent hyperthermia in combination with radiation therapy. Locoregional hyperthermia was administered once or twice a week for 40-60 min to a total of 2-14 sessions using RF capacitive or microwave heating equipment. Radiation therapy was given 10-20 min before hyperthermia at doses of 20.8 to 70 Gy. The mean +/- SD of the maximum, average, and minimum intratumour temperatures was 44.0 +/- 2.9 degrees C, 42.3 +/- 1.6 degrees C, 40.1 +/- 1.1 degree C respectively, and that of the percentage of the intratumour points that exceeded 41 and 43 degrees C was 66.0 +/- 33.6, and 31.0 +/- 26.1 respectively. Of the 31 tumours treated, 13 (42%) showed CR (complete regression), 10 (32%) PR (> 50 and < 100% regression) and 8 (26%) NC (< 50% regression). Since intratumour low density areas on post-treatment CT scans have been demonstrated to be a useful parameter for assessing tumour response to thermoradiotherapy, the presence of low density areas was also assessed. Low density areas were classified into the following three categories according to the percent area occupied in the maximal cross-section of the tumour: type I, < 50%, type II, 50-80%; type III, > 80%. Of 20 tumours evaluable, 6 (30%) exhibited type III change, 11 (55%) type II and 3 (15%) type I. All of the type III tumours demonstrated a marked response on follow-up or histopathological examination. The major complication associated with treatment was skin ulcer in two patients. The five-year survival of the total 27 patients and 18 patients who had no distant metastases at the start of treatment was 32 and 48% respectively. These results indicate the clinical benefit of thermoradiotherapy using RF capacitive or microwave equipment for locally advanced and/or recurrent soft tissue tumours.

Clinical system for simultaneous external superficial microwave hyperthermia and cobalt-60 radiation

A system for simultaneous thermoradiotherapy was devised to investigate the possible benefits and/or complications of thermal radiosensitization in human superficial tumours. The system combines the well-known treatment modalities of external 915 MHz microwave hyperthermia and cobalt-60 teletherapy. Single waveguide applicators are utilized either attached to blocking trays, so that the gamma beam travels through a waveguide and into the patient (en face setup), or in a conventional way with the microwave propagation vector orthogonal to the gamma beam (orthogonal setup). With these setups a radiation fraction can be delivered in the middle of a 60-min, non-interrupted hyperthermia treatment. Temperatures and power level are remotely monitored and recorded outside the Cobalt room. Extensive measurements and testing showed that the operation of the hyperthermia system (generator, applicators, thermometry unit and temperature sensors) was not disrupted by irradiation and that the microwaves were confined to the treatment room and did not interfere with the operation of the Cobalt unit, of an adjacent linear accelerator or of an adjacent radiotherapy simulator. For the en face setup the dose distributions induced in solid water phantoms were uniform with the exception of a narrow (< 0.5 cm) region under the applicators' internal probes where 10-18% reduction exists. This dose defect is clinically smoothed using feathering techniques. The system has been successfully used without technical problems in 51 treatments in 15 patients (18 lesions) in a phase I/II clinical trial. An analysis of the thermal data showed that the temperature distributions achieved during simultaneous delivery have the same general characteristics of those achieved in conventional sequential hyperthermia with microwaves, and that the steady state distributions are maintained during the time of simultaneous irradiation. The tests performed in addition to the preliminary clinical experience clearly indicate that this type of combined therapy is technically feasible and safe. Here the system for simultaneous, external, superficial thermoradiotherapy and the implementation tests performed are described in detail. Preliminary clinical experience and results are also reported.

Clinical evaluation of 430 MHz microwave hyperthermia system with lens applicator for cancer therapy

The clinical efficacy of a microwave (MW) hyperthermia system using an electric-field converging (lens) applicator is evaluated for 42 malignant tumours with a maximum tumour depth of less than 7 cm. The mean of the maximum, average and minimum tumour temperature of the 42 tumours are 44.5, 42.5 and 40.7 C, respectively. The thermal parameters are higher for tumours in the chest, abdominal walls and hip than for those in the neck, groin and extremities. No apparent difference in thermal parameters according to the depth of tumour is shown. Of 40 tumours treated by hyperthermia in combination with radiotherapy, 20 (50%) showed complete regression, 14 (35%) showed partial regression, and six (15%) showed no change. This phase I and II study indicates clinical feasibility of the newly developed MW heating apparatus, and strongly suggests the usefulness of thermoradiotherapy in the treatment of localised superficial and subsurface malignancies.

Clinical hyperthermia with a new device: the current sheet applicator

PURPOSE

The current sheet applicator (CSA) is a newly developed microwave hyperthermia device. Advantages over commercial microwave applicators include its small size and high ratio of heating area to physical aperture area. These physical characteristics make the CSA excellent for heating constricted areas and allow the use of arrays of CSAs over large surfaces. This study examines the clinical efficacy of the CSA for heating superficial malignant tumors.

METHODS AND MATERIALS

From December 1989 through October 1991, 19 patients with recurrent or metastatic superficial malignant tumors were treated once or twice weekly to 30 hyperthermia fields using one to four CSAs. Each field received from one to four hyperthermia treatments for a total of 74 treatments. The treatment objective was to elevate the tumor temperature to a minimum of 42.5 degrees C for 30 min (2 patients) or 60 min (17 patients). Intratumor temperatures were measured with percutaneous fiberoptic thermometry probes. All patients received concurrent fractionated radiation therapy with total dose ranging from 20 to 65 Gy (median 46 Gy). Seventeen of the 30 fields had been previously irradiated to a median dose of 50 Gy.

RESULTS

Mean values for the maximum temperature, average temperature, and minimum temperature were 43.6 degrees C +/- 1.0, 42.2 degrees C +/- 1.4, and 41.0 degrees C +/- 1.5, respectively. Mean values for T50 and T90 were 42.2 degrees C +/- 1.1 and 41.0 degrees C +/- 1.3, respectively. The overall response rate for all assessable fields was 96%. Only Only three responding tumors have progressed with a median follow-up period of 6 months. Treatment related morbidity was generally mild and self-limited.

CONCLUSION

The CSA is a promising new microwave hyperthermia device capable of heating superficial tumors to therapeutic temperatures. When used in combination with radiotherapy, response rates are excellent without excessive toxicity.

Radio-frequency ring applicator: energy distributions measured in the CDRH phantom

SAR distributions were measured in the CDRH phantom, a 1 cm fat-equivalent shell filled with an abdomen-equivalent liquid (sigma = 0.4-1.0 S m-1; dimensions 22 x 32 x 57 cm) to demonstrate the feasibility of the ring applicator to obtain deep heating. The ring electrodes were fixed in a PVC tube; diameter 48 cm, ring width 20 cm and gap width between both rings 31.6 cm. Radio-frequency energy was fed to the electrodes at eight points. The medium between the electrodes and the phantom was deionised water. The SAR distribution in the liquid tissue volume was obtained by a scanning E-field probe measuring the E-field in all three directions. With equal amplitude and phase applied to all feeding points, a uniform SAR distribution was measured in the central cross-section at 30 MHz. With RF energy supplied to only four adjacent feeding points (others were connected to a 50 omega load), the feasibility to perform amplitude steering was demonstrated; SAR values above 50% of the maximum SAR were measured in one quadrant only. SAR distributions obtained at 70 MHz showed an improved focusing ability; a maximum at the centre exists for an electric conductivity of the abdomen-equivalent tissue of 0.6 and 0.4 S m-1.

Hyperthermia equipment evaluation

This article looks briefly at the advances over the past 2 decades in the development of equipment for administering clinical hyperthermia, and observes that while there has been much progress, the equipment available today still does not meet the design criteria articulated 20 years ago. The assertation is made that the testing of hyperthermia equipment in animals has not addressed the questions most of interest in the clinic, and a suggestion is made for a more rigorous way to evaluate clinical equipment. Finally some areas where significant progress in equipment development seems possible are mentioned.

Thermometry of interstitial hyperthermia given as an adjuvant to brachytherapy for the treatment of carcinoma of the prostate

PURPOSE

Recurrence in the prostatic gland remains a significant problem in the management of locally advanced prostatic cancer. Transperineal thermobrachytherapy has been utilized in an attempt to improve local tumor control. The purpose of this study was to quantitate the temperature distributions obtained in carcinoma of the prostate treated with interstitial radiofrequency-induced hyperthermia given in conjunction with 192Ir brachytherapy in a Phase I study.

METHODS AND MATERIALS

From 1987 until 1992, 36 patients (5 with locally recurrent, 15 with Stage B, and 16 Stage C prostate cancers) were treated with interstitial brachytherapy implants supplemented with radiofrequency-induced hyperthermia. An array of 7-32 stainless steel trocar electrodes (outer diameter = 1.5 mm, interelectrode spacing = 8 mm) were implanted into the prostate gland through a perineal approach utilizing a specially designed template. Each trocar was electrically insulated along the length which traversed surrounding normal tissues. One to three additional plastic catheters were implanted for automated temperature mapping. Thirty-four of these procedures were performed following lymph node sampling. However, the last two removable interstitial hyperthermic prostate implants were done by the transperineal route under ultrasound guidance. A hyperthermia treatment (goal of 43 degrees C for 45 minutes) was given immediately prior to the insertion and immediately following the removal of the 192Ir. A computer-controlled radiofrequency-based generator (freq. 0.5 MHz) implementing electrode multiplexing was used to induce and maintain elevated temperatures.

RESULTS

Transient local pain was the most common treatment limiting factor. The average values of the measured minimum, mean, and maximum temperatures were 38.9 degrees C, 41.9 degrees C, and 45.7 degrees C in tumor, and 37.7 degrees C, 39.8 degrees C, and 42.9 degrees C in surrounding normal tissue, respectively. The percentages of mapped temperatures exceeding 41 degrees C, 42 degrees C, and 43 degrees C were 67%, 46%, and 27% in tumor, and 26%, 11%, and 4% in normal surrounding tissue, respectively.

CONCLUSION

From this study we conclude that heterogeneous temperature distributions were induced in the prostate; significant normal tissue protection was realized in part through the selective insulation of sections of each electrode; and interstitial radiofrequency-induced hyperthermia of the prostate is feasible and well tolerated, with further technical developments warranted.

Hyperthermic enhancement of high dose-rate irradiation in 9L gliosarcoma cells

PURPOSE

Long duration-mild temperature hyperthermia has previously been shown to be an effective potentiator of low-dose-rate irradiation. An in vitro investigation was initiated to determine if 41 degrees C hyperthermia could be useful in sensitizing high-dose-rate (HDR) brachytherapy. Experiments were designed to determine the optimal length of heat treatments to be applied with a twice daily 5 Gy times five fraction high-dose-rate protocol.

METHODS AND MATERIALS

Rat 9L gliosarcoma cells growing exponentially in flasks were exposed to X-irradiation and 41 degrees C hyperthermia. Irradiation was applied in 5 Gy fractions two times per day to a total dose of 25 Gy. Hyperthermia consisted of combinations of 1 or 4 hr heating before and/or after each of the radiation exposures. In addition, a set of cells was heated continuously at 41 degrees C starting 6 hr before the first fraction and continuing to 4 hr after the 5th fraction. Cell survival was assayed by colony formation.

RESULTS

Sensitization of high-dose-rate increased linearly with increasing length of 41 degrees C heating over the entire range of heat exposures applied. Maximum sensitization was produced by continuous heating for 58 hr throughout the entire radiation course. Heating for 4 hr before fractions two through five produced less sensitization to these later fractions than was expected if each heat-radiation fraction had acted independent of the other fractions.

CONCLUSION

Continuous 41 degrees C heating eliminated split dose sparing during high-dose-rate. The apparent development of thermotolerance during the course of heat and high-dose-rate resulted in reduced sensitization in the later fractions when 4 hr pre- and/or post-heat were applied. This tolerance was overcome if heat was applied continuously between radiation fractions. The clinical relevance of these in vitro data is that 41 degrees C hyperthermia should be applied for as long as is possible during this type of high-dose-rate protocol. This combined hyperthermia-high-dose-rate treatment may enhance the efficacy of interstitial irradiation in situations such as boost irradiation of high grade glioma.

Interstitial hyperthermia and high dose rate brachytherapy in the treatment of anal cancer: a phase I/II study

PURPOSE

The rate of local failure is sufficiently high following sphincter conserving surgery and radiation therapy for advanced anal cancers to warrant investigation of improved local treatment techniques. This Phase I/II study was undertaken to investigate the site-specific toxicities and response of Stage II and III anal cancers to interstitial thermoradiotherapy using a hot water interstitial system.

METHODS AND MATERIALS

Between September 1988 and March 1991, 14 patients with primary carcinomas of the anal canal, UICC Stage T2-3, N0-1, M0, were treated with split-course external beam irradiation to the pelvis (30 Gy + 20 Gy) and 1 or 2 interstitial Iridium-192 high dose rate (Ir-192 HDR) implants (6-8 Gy each) immediately followed by interstitial hyperthermia (HT). Patients with tumor diameters > 3 cm were scheduled to receive chemotherapy consisting of 2 courses of 5-fluorouracil and mitomycin C given concomitantly with external beam radiation. Interstitial hyperthermia was induced by circulating warm water through the needles that were implanted to hold the Ir-192 source. The treatment goal was to achieve and maintain a temperature of 42.5 degrees C over a time period of 40 min. A 3-point thermocouple probe inserted into one or two additional needles was used for thermometry. The temperatures were recorded by manual mapping along these needles at steps of 0.5 or 1 cm.

RESULTS

A total of 20 Ir-192 HDR-HT implants were performed in 14 patients. All but two patients completed the external beam irradiation; five patients received concomitant chemotherapy. Analysis of thermal parameters showed that minimum intratumoral temperatures (Tmin) of 42 degrees C, 42.5 degrees C, 43 degrees C, and 44 degrees C were achieved in 64%, 37.5%, 14%, and 7% of patients, respectively. Intratumoral mean Tmin, mean average, and mean maximum temperatures for these patients were 41.7 degrees C, 42.4 degrees C, and 43.4 degrees C, respectively. Brachytherapy and HT were well tolerated. Clinical complete responses (cCR) were obtained in 11/14 (78.5%) patients, complete histopathological responses (pCR) in 10/14 (71%). Only one patient with pCR recurred and succumbed to her disease. Patients with persistent disease (1 minimal and 3 partial responders, including 1 cCR) underwent abdominal-perineal resection but subsequently died from local-regional recurrence. One patient with pCR died from unrelated causes. Median survival for all patients from onset of radiation to death or last follow-up is 26 months. Eight patients are alive disease-free after a follow-up ranging from 16-44 months (median: 30, mean: 30 months). Treatment complications were limited to two patients who developed persistent ulcers. Sphincter function was maintained in 50% of patients.

CONCLUSION

This study demonstrates that interstitial warm water hyperthermia in combination with brachytherapy for anal carcinomas is feasible and did not add to complications when compared to studies employing external beam irradiation and brachytherapy alone. The thermal parameters obtained by the warm water system compare favorably to those reported by others using radiofrequency and microwave systems.

Prognostic factors in metastatic malignant melanoma treated with combined radiation therapy and hyperthermia

From May 1981 to September 1991, 38 patients with metastatic malignant melanoma were treated with combined radiation therapy and hyperthermia to a total of 97 hyperthermia treatment fields. Prior treatments to these sites included surgery (31 patients, 76 fields), chemotherapy (18 patients, 54 fields), immunotherapy (14 patients, 42 fields) and radiation therapy (7 patients, 13 hyperthermia fields). Hyperthermia was given to fields located in the head and neck region, trunk and extremities in 30, 45 and 22 cases, respectively. Nodular-diffuse tumours were present in 86 fields while 11 fields were treated for microscopic residual tumour deposits. Concurrent radiation therapy was given in 180-400 cGy per fraction, 2-5 times per week for a mean total dose of 4098 cGy per field. Hyperthermia treatments were delivered using either microwave or ultrasound devices (286 and 48 treatments, respectively) with a mean (range) of 3.4 (1-14) hyperthermia treatments per field for a mean (range) of 43 (10-70) min per field. Patients (n = 34; 84 fields) were available for follow-up for a mean (range) of 14.6 (0.4-82.5) months. At 3 weeks post-treatment, 34 fields had complete, ongoing, or partial responses; 39 fields had no response; and there were no recurrences in the 11 fields treated for microscopic residual disease. Local control was maintained in 31% (26/84) fields with a mean follow-up of 14.6 months. At 36 months, five patients remained alive with complete control of their treated local disease. Statistical analyses revealed that patients with soft tissue metastases only, who were older at the time of hyperthermia, had a longer time between initial diagnosis and hyperthermia treatment, received a higher dose of radiation, had no previous chemotherapy, and had small tumour volumes, had a higher initial response. Multivariate analyses revealed that the three-covariate model including time interval between initial diagnosis and hyperthermia treatment, previous chemotherapy, and metastases to soft tissue only, best predicted response. The results of the investigation support the continued study of combined radiation therapy and hyperthermia treatments for selected patients with metastatic melanoma, and indicate that long-term survival can occasionally be obtained with this approach.

Temperature differentials between treatment and pretreatment temperatures correlate with local control following radiotherapy and hyperthermia

PURPOSE

To evaluate the influence of pretreatment tumor temperatures and the temperature differential between treatment and pretreatment temperatures on local tumor control in patients who underwent combined radiation therapy and hyperthermia.

METHODS AND MATERIALS

Mapped intratumoral temperatures were measured immediately prior to and during hyperthermia in 138 hyperthermia fields among 59 patients with nodular (60 fields) or diffuse (78 fields) superficially-located tumors. In the nodular subgroup there were 40 fields with adenocarcinomas (31 breast, two prostate, seven other primary sites), six melanomas, nine squamous cell carcinomas, and five other histologies. The fields with diffuse tumor involvement consisted of 77 adenocarcinomas (67 breast, 10 other) and one melanoma. The maximum, minimum, and average temperatures were determined for both the pretreatment (pTmax, pTmin, pTave) and treatment (Tmax, Tmin, Tave) distributions and the differences, Dm = Tmin-pTmax, and Da = Tmin-pTave, computed. These quantities were averaged over treatments to produce the corresponding mean quantities for each hyperthermia field. Univariate and multivariate analyses were performed to determine treatment and pretreatment parameters which best correlated with the duration of local control.

RESULTS

Pretreatment tumor temperatures were significantly lower than the oral temperatures with mean pTmax, mean pTmin, and mean pTave of 36.2 degrees C, 34.2 degrees C, and 35.4 degrees C, respectively. For the adenocarcinomas with diffuse involvement within the hyperthermia field, the covariates best correlating with local control duration on univariate analysis were concurrent radiation dose (p = 0.0026), Dm (p = 0.009), pTmax (p = 0.012) and Da (p = 0.036). Lower pTmax and larger Dm and Da were predictive for longer local control. In multivariate analyses, all thermal parameters lost power, however, the best model included Dm which was significant at the p = 0.040 level. For the nodular subgroup, nonthermal parameters and dichotomized thermal parameters were of prognostic significance for local control.

CONCLUSION

For fields diffusely involved with adenocarcinoma significant correlations with duration of local control have been demonstrated both for a) low pretreatment temperatures and b) large differentials between treatment and pretreatment intratumoral temperatures. These correlations were also found in a dichotomized description for fields with nodular tumors. The results support the concept that pretreatment hypothermic conditions can lead to an increase in thermal sensitization and may help explain the excellent clinical results noted in the treatment of superficial tumors with radiation and hyperthermia. Further exploitation of this approach by planned cooling of superficially-located recurrent tumors prior to hyperthermia treatment warrants investigation.

Analysis of temperature distributions of interstitial hyperthermia using a hot water system

PURPOSE

Interstitial hyperthermia is being increasingly used as an adjunct to brachytherapy in the treatment of implantable tumors. Of the several interstitial hyperthermia systems available, perhaps the simplest to use are the circulating hot water systems. An analysis of the thermal distributions obtained during our initial experience with interstitial hyperthermia using steel needles and the KHS-9 hot water system was therefore undertaken.

METHODS AND MATERIALS

Between September 1988 and June 1991, 23 patients were treated with interstitial Iridium-192 high dose-rate brachytherapy immediately followed by interstitial hot water hyperthermia. A total of 32 implants were performed in these patients, of whom 14 presented with primary anal carcinomas, six with recurrent gynecological tumors, and three with subcutaneous metastases from malignant melanoma. All but the patients with anal cancers had failed in previously irradiated sites. One or two heat treatments were delivered to each tumor with the goal to reach and maintain an intratumoral temperature 42.5 degrees C over a period of 40 min. Temperature measurements were carried out by mapping three-point thermocouple probes along the track of one or two needles parallel to the implanted needles.

RESULTS

Minimum intratumoral temperatures exceeded 42.0 degrees C in 41%, 42.5 degrees C in 19%, 43.0 degrees C in 13%, and 44.0 degrees C in 3% of treatments. The average minimum, maximum, and mean intratumoral temperatures for all treatments were 41.7 degrees C, 43.5 degrees C, and 42.6 degrees C, respectively.

CONCLUSION

The temperature profiles obtained in this series compare favorable to those reported in literature for radiofrequency local current field systems and suggest the hot water device may be an alternative heating method. It is relatively simple to use, does not require shielding of the treatment room, and can easily be adapted to currently used brachytherapy systems. Further patient accrual and longer follow-up will be needed to assess the clinical results in terms of tumor response and duration of response.

Present and future status of noninvasive selective deep heating using RF in hyperthermia

To achieve hyperthermia using electromagnetic energy, RF of under 100 MHz is basically suitable for the external heating of the deep portions of the body. For applicators using such RF, the following types are considered: capacitive, inductive, radiative and hybrid. With radiative applicators, the intensity of the EM waves radiated from the applicator decreases with propagation into the material to be heated, but the phased annular array of radiative applicators potentially increases the intensity of the EM energy in the deep portion owing to the interference of the waves. Using this method, the focusing of EM energy depends on the dielectric properties of the material to be heated. With respect to RF heating at a lower frequency than the RF used for the annular phased array, some devices have been said to concentrate EM energy in the deep portions, where the characteristics of 'wave' are not utilised. To this end, some methods using capacitive electrodes, an inductive coil, or a combination of both, are being designed. The results of using such methods have shown that it is possible to supply sufficient EM energy to the muscle layers deep in the material to be heated, without heating the fat layers excessively.

Deep regional hyperthermia: comparison between the annular phased array and the sigma-60 applicator in the same patients

PURPOSE

Several institutions have accumulated clinical experience with the annular array as well as with the Sigma applicator. There exist only limited data in comparison of both heating devices possibly favoring the annular array over the Sigma applicator with regard to tumor temperatures and acute toxicity. The objective of this study was to record temperature distributions at identical sites in tumor and normal tissue in the same patients treated with each device.

METHODS AND MATERIALS

Eighteen patients with advanced pelvic tumors were treated on successive occasions with regional hyperthermia using the annular phased array applicator usually driven at 60-80 MHz or the Sigma applicator usually driven at 70-90 MHz. In all patients detailed thermal mapping and temperature analysis for tumor and normal tissues could be performed.

RESULTS

Regardless the device used the acute toxicity was treatment limiting in nearly 50% of the treatments. Systemic stress was treatment limiting in 30% of the treatments with both devices although systemic parameters (core temperature, heart rate, changes in blood pressure) were higher with the annular array. The overall mean minimum, average and maximum tumor temperature observed were 39.5 +/- 1.0 degrees C, 40.9 +/- 1.4 degrees C, 42.7 +/- 2.3 degrees C for the annular array and 39.3 +/- 0.9 degrees C, 40.9 +/- 1.4 degrees C, and 42.5 +/- 1.7 degrees C for the Sigma applicator. The time-averaged temperatures achieved in 20% (T20), 50% (T50) and 90% (T90) of all measured sites were 41.7 +/- 2.1 degrees C, 40.8 +/- 1.4 degrees C, 39.9 +/- 1.2 degrees C for the annular array and 41.7 +/- 1.4 degrees C, 41.0 +/- 1.3 degrees C, and 40.1 +/- 1.0 degrees C, for the S-60. The difference was not statistically significant. With regard to normal tissue temperatures a trend to higher maximum temperatures in the deep muscle and fat tissue was evident for the Sigma applicator. The overall minimum and average normal tissue temperatures in the deep muscle and fat tissue and the rectum and the time-averaged temperatures achieved in 20% (T20), 50% (T50) and 90% (T90) of the measured sites differ not statistically significant.

CONCLUSION

These results indicate that there continue to be unresolved limitations in achieving temperature elevation in deep seated tumors of the pelvis with radiative coherent EM wave techniques using amplitude and phase steering capabilities without any special optimization procedure.

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.

Pre-clinical evaluation of a microwave planar array applicator for superficial hyperthermia

Multi-element hyperthermia applicators have an advantage over single-aperture devices in that the power deposition pattern across the applicator surface may be adjusted to improve the resultant temperature distribution. This capability can be used to compensate for irregular tumour geometry as well as heterogeneity of thermal and power absorption parameters within the tissue. This paper evaluates the first commercially available microwave system of this type designed for superficial hyperthermia. The applicator (16-element planar array, 915 MHz, 15.2 x 15.2 cm footprint) was evaluated by the following: (1) measuring absolute SAR distributions in muscle-equivalent liquid phantom with an intervening 1 cm thick layer of fat phantom by scanning a calibrated E-field sensor, and (2) power output measurements using calorimetric methods. The SAR distributions measured for each individual aperture exhibited significant irregularities and differing power deposition patterns. A priori knowledge of these different power deposition characteristics was used to provide appropriate illumination schemes which could be used as initial starting points for producing clinically useful power deposition patterns. Measurements of these composite patterns demonstrate the adjustable nature and flexibility of the heating capabilities of this applicator, which includes 50% iso-SAR coverage that can be extended to the applicator perimeter. This clearly illustrates the clinical utility and potential advantages of this system over single-aperture devices for superficial hyperthermia.

Problems associated with CT-guided catheter insertions

From October 1987 to August 1991 a total of 141 closed-tip catheters were inserted into deep-seated or half-deep-seated tumours in 95 treatment areas. Most of the catheters (n = 79) were implanted in the pelvic region. In 139 punctures no clinical evidence of bleeding was seen. A transient blood loss was evident in only two patients. In addition, no nerve injury was observed. The problems with 141 implanted catheters were evaluated. Nineteen catheters (13%) were lost during the treatment series. In five displacement of the catheters was verified by repeat CT scans during the whole treatment. Eight catheters had to be removed due to infection. In two patients with advanced disease who were receiving a combination of chemotherapy and hyperthermia a strong inflammatory response was evident. Another patient developed an acute pancreatitis after catheter insertion. No metastasis in the invasive tracks has been seen in the follow-up period. In conclusion the insertion of closed-tip catheters by CT guidance is a sure and well-tolerated method. There were a few problems only with the implanted catheters throughout the whole treatment series.

Thermoradiotherapy in locally advanced deep seated tumours--thermal parameters and treatment results

From October 1987 to December 1990 a total of 37 patients with deep seated tumours of the pelvis (n = 34), the abdomen (n = 2), or lower leg (n = 1) were treated with radiotherapy and regional hyperthermia. Hyperthermia was produced by the BSD-1000 system and the annular phased array (AA) applicator usually driven at 60-80 MHz, or the BSD-2000 system and the Sigma-60 (S 60) applicator usually driven at 70-90 MHz. Detailed thermal mapping and temperature analysis was performed on 29 patients. The overall mean maximum, average and minimum temperature observed was 42.9 +/- 2.4 degrees C, 40.9 +/- 1.5 degrees C, and 39.3 +/- 0.9 degrees C for all treatments. The time-averaged tumour temperatures achieved in 20%, 50% and 90% of all measured temperature sites were 41.8 +/- 2.1 degrees C (T20), 40.9 +/- 1.6 degrees C (T50), and 39.9 +/- 1.2 degrees C (T90). In addition, the overall mean maximum, average and minimum temperature measured in normal tissue was 42.4 +/- 1.4 degrees C, 40.6 +/- 1.0 degrees C, and 39.2 +/- 0.9 degrees C. The time averaged normal tissue temperatures achieved in 20%, 50% and 90% of all measured temperature sites were 41.3 +/- 1.1 degrees C, 40.6 +/- 1.1 degrees C, and 39.6 +/- 1.0 degrees C. In 36 assessable patients, the overall objective response rate was 31%: 2 complete responses (CR) and 9 partial responses (PR).

Local hyperthermia, radiation therapy, and chemotherapy in patients with local-regional recurrence of breast carcinoma

We retrospectively reviewed the response rate and the acute and long-term toxicity of combined treatment using radiation therapy, hyperthermia, and chemotherapy in 29 patients with locally or regionally recurrent or advanced adenocarcinoma of the breast who completed at least 4 of the 6 prescribed hyperthermia treatments as part of a Phase I-II trial. Thirty-nine separate hyperthermia treatment fields were evaluated. Cisplatin alone or cisplatin with etanidazole or bleomycin was delivered just prior to hyperthermia once weekly. Hyperthermia was delivered to a target minimum tumor temperature of 43 degrees C +/- 0.5 for 60 min. Following hyperthermia, a 400 cGy fraction of radiation was given. The radiation fraction size on other days was 200 cGy. Twenty-two fields had previously been irradiated and 17 fields had not. Prior chemotherapy had been given in 24 of 29 patients (83%) and hormonal therapy given in 21 (72%). The median follow-up time is 10 months; 16/29 patients (55%) have died of disease. The overall complete response rate for all fields was 53%. Response rate was not related to any clinical factor, radiation dose, microwave or ultrasound technique, type of chemotherapy, or tumor temperatures, but the number of patients in the study population was small. A statistically significant association between the likelihood of complications and the total radiation therapy dose (previous radiation and present radiation) was found. Persistent ulceration lasting greater than 1 month after completing treatment was seen in 67% of previously irradiated fields compared to 21% of fields that had not been previously treated (p = 0.015). Surgical wound repair was needed for 38% of fields with a history of prior irradiation versus 6% of those without prior treatment (p = 0.050). A statistically significant radiation therapy dose response was found for the likelihood of these complications. None of the hyperthermia temperature parameters studied correlated with an increased risk of complication. We conclude that the combination of radiation therapy, hyperthermia, and chemotherapy results in a high rate of complete response. However, in patients who have been treated with prior radiation therapy, this combination may be more locally toxic than treatment with hyperthermia and radiation therapy alone. The precise impact of chemotherapy on the therapeutic index of hyperthermia and radiation therapy remains to be determined in randomized clinical trials.

Persistent and/or late complications of combined radiation therapy and hyperthermia

Persistent and/or late complications were analysed in 64 patients (183 fields) that were treated with combined hyperthermia and radiation therapy for advanced, recurrent or metastatic cancer. The incidence and type of complications were evaluated over a minimum follow-up period of 2 years from the onset of treatment (mean 38.7 months; range 24-82.5 months). The primary malignancies included: breast (39), melanomas (6), adenoid cystic carcinomas of salivary glands (4), prostate (4), soft tissue sarcomas (3), squamous cell carcinoma of head and neck (3), lymphomas (3), transitional cell carcinoma of bladder (1) and basal cell carcinoma of the skin (1). The persistent complications noted included induration and fibrosis (39 hyperthermia fields, 22 patients), ulceration at the site of prior tumour (three patients, three fields), and ulceration in normal tissue (one patient, one field). Brachial plexopathy developed in one patient treated for recurrent breast cancer, but she had active disease at that time. A squamous cell carcinoma of the skin developed within the treatment field in a breast cancer patient. Radionecrosis of the mandible was seen in one patient treated for a floor of the mouth cancer, and osteomyelitis with septic arthritis developed in one patient treated for a soft tissue sarcoma of the thigh. Univariate logistic regression analyses of pretreatment and radiation-hyperthermia treatment parameters revealed that maximal tumour temperature had a borderline significant correlation with the development of complications (p = 0.07). Multivariate analyses of the pretreatment and treatment parameters revealed the best-two-covariate model to predict complications included mean maximal tumour temperature and tumour type (macroscopic tumours had greater incidence of complications than for microscopic residual disease). The rate and type of persistent and/or late complications seen following combined radiation and hyperthermia did not appear to dramatically differ from those that would be anticipated from irradiation alone in this patient population, with the exception of an increased incidence of areas of induration and tumour necrosis.

Potential hazards of radiative electromagnetic hyperthermia in the presence of multiple metallic surgical clips

Three-dimensional computer simulations of a patient under consideration for heating by the BSD Sigma 60 phased array applicator showed marked specific absorption rate (SAR) enhancement in the region where there was a concentration of metallic surgical clips. Subsequent tests in tissue-equivalent phantom material confirmed that metallic objects much shorter than the wavelength in tissue of the radiative electromagnetic field can cause significant changes in the power deposition near the implanted metal. The placement of extensive numbers of surgical clips may therefore hinder the ability to subsequently utilize radiative electromagnetic heating modalities.

Radiofrequency capacitive heating of deep-seated tumours using pre-cooling of the subcutaneous tissues: results on thermometry in Dutch patients

The capacity of a radiofrequency, 13.56 MHz, capacitive hyperthermia system using extensive pre-cooling of the subcutaneous tissue to induce locoregional deep heating has been investigated in 11 patients. Tumour location was presacral in nine--and eccentric towards the lateral side of the pelvis in two patients. For thermometry multiple catheters (mean 2.7) were inserted into the treatment volume. The mean numbers of temperature measuring points per treatment were 9.4 in tumour, 5.5 in muscle and 7.2 in subcutaneous fat. RF energy was applied after 30 min of cooling through two flexible boli perfused with saline water at 5-10 degrees C. Patient tolerance to pre-cooling was very good and after some initial discomfort the patient became rapidly accustomed to the cold water boli. For some patients better temperatures were achieved when the conventional anterior-posterior applicator set-up was replaced by a set-up with an applicator on each lateral side of the patient. As patients can tolerate temperatures within the fat tissue as high as 45.5 degrees C without complaining it appears important to monitor the temperature at the transition of fat to muscle tissue to prevent subcutaneous burns. The study shows that pre-cooling cannot avoid preferential heating at the interface from fat to muscle tissue. In this patient group the quality of the hyperthermia treatment appeared to be rather poor: 60% of the measured tumour temperatures were below 40 degrees D.

Correlation of thermal parameters with outcome in combined radiation therapy-hyperthermia trials

Many studies utilizing combined hyperthermia (HT) and radiation therapy (XRT) in the treatment of advanced or recurrent malignancies have reported a correlation between some measure of the minimum temperature achieved and outcome. Previous reported studies at Stanford have demonstrated a statistically significant correlation between the duration of local control and Tmin, the mean over treatments of the minima of (a) measured intratumoral temperatures in fields which contained diffuse or nodular tumours, or (b) measured interstitial temperatures in fields treated for microscopic residual disease. Recently, T90, the mean of the temperatures above which 90% of all measured intratumoral temperatures fall, has been proposed as an alternative characterization of the efficacy of the HT treatment that reportedly has a superior correlation with outcome. To test this hypothesis, T90 was computed by two different methods for three groups of patients treated at Stanford with XRT-HT for superficially located tumor recurrences. Tmin was found to be strongly correlated with T90 calculated by both methods. All three thermal parameters correlated with complete response at 3 weeks and with local control, although Tmin usually demonstrated the strongest correlation.

Early experience of a commercial scanned focused ultrasound hyperthermia system

Preliminary experiences of the Sonotherm 6500 scanned focused ultrasound (SFUS) system in the hyperthermic treatment of bulky tumours in breast, superficial sites and within the pelvis in 22 patients are reported. Tumour volumes ranged from 235 to 603 cm3 (breast), 105 to 209 cm3 (superficial sites) and 24 to 905 cm3 (pelvis). Temperature distributions in 58 evaluable treatments were analysed in terms of temporal peak and time-averaged temperatures (highest and lowest temperatures, percentage of sensors exceeding index temperatures, etc.) achieved within scanned volumes. Mean number of sensors implanted into tumour was 14 in breast and superficial tumours and approximately 11 in pelvic tumours. Mean time-averaged maximum and minimum temperatures for the best treatments (i.e. for each patient, that with the highest percentage of sensors recording time averaged temperatures greater than or equal to 42 degrees C) administered to patients with tumours in the breast and superficial sites were 44.6 +/- 1.7 degrees C and 39.7 +/- 1.1 degrees C, respectively and the mean number of sensors exceeding 42 degrees C was 58 +/- 19%. In the case of pelvic tumours these figures were 41.6 +/- 0.9 degrees C, 40.0 +/- 0.6 degrees C and 8 +/- 12%, respectively. Patient tolerance to treatments was, in general, good. Areas where technical improvement of the system is appropriate and further research and development are required are identified; these should lead to a better realization of the potential of the SFUS technique, particularly for pelvic tumours.

Direct use of CT scans for hyperthermia treatment planning

In the field of deep regional hyperthermia cancer therapy, the BSD-2000 Hyperthermia System is one of the most widely used devices. Because of the complexity of the treatment process, computer modeling has long been viewed as a desirable means of planning patient treatments. Patient-specific, three-dimensional computer modeling for treatment planning in the BSD-2000 has been in clinical use at this institution for two years. Two of the persistent problems have been the large amount of time needed to create the patient model from a computed tomography (CT) scan (one and a half days), and the lack of a way to view the large amounts of data that comprise the output of a treatment plan, i.e., the specific absorption rate (SAR) at 20,000 to 30,000 cells. Here we present a method that obtains the dielectric properties needed for hyperthermia treatment planning directly from the CT image with minimum operator interaction, a process which takes about a half day and is more accurate. Comparison is made with the previous method of drawing contours around the different tissue types. We further describe a method which displays the output as iso-SAR contours directly over the CT scan of the patient.

Automated mechanical thermometry probe mapping systems for hyperthermia

In order to better assess temperature distribution patterns in patients, tissue equivalent phantoms, and experimental animals, mechanical devices and automated control systems for positioning temperature probes in implanted catheters and catheters laid on the skin surface have been developed. They employ stepper motor actuated roller and idler wheel drives to move the probes. Two devices incorporate positive positioners in addition to the drive rollers in order to obtain higher positioning accuracy where significant probe to catheter friction is present. Automated systems have been constructed which can simultaneously position, record and display data from up to 10 temperature sensors in a colour-coded position versus temperature format to produce a real time two-dimensional colour-coded pseudo isotherm display. These thermal mapping devices have been used for characterizing the power deposition patterns of several large area microwave applicators (on the surface and at depth within tissue equivalent phantoms), for intraorgan temperature mapping in experimental animals, and for surface and subcutaneous temperature mapping during clinical treatments.

Cancer metastatic to the penis: treatment with hyperthermia and radiation therapy and review of the literature

Metastatic cancer to the penis is rare, its optimum treatment remains poorly defined and the outcome of patients with such metastases is poor. Hyperthermia in conjunction with radiation therapy has been shown to be an effective modality in the treatment of locally advanced or recurrent cancer and hyperthermia alone is under evaluation in treating benign disorders, such as hypertrophy of the prostate. Recently, 4 patients with symptomatic metastatic lesions to the penis (3 had primary prostatic cancer and 1 had rectal cancer) were treated with radiation therapy and hyperthermia. Treatment was well tolerated except for pain during hyperthermia, which limited the temperatures that could be obtained. All of the patients improved symptomatically, 1 achieved a complete response and 2 had partial responses. No significant complications were noted. Symptomatic control was maintained in all patients for the duration of their survival. This limited series suggests the possible role of local hyperthermia as an adjunct to radiation therapy in the treatment of metastases to the penis.

Body conformable 915 MHz microstrip array applicators for large surface area hyperthermia

The optimal treatment with hyperthermia of superficially located tumors which involve large surface areas requires applicators which can physically conform to body contours, and locally alter their power deposition patterns to adjust for nonuniform temperature caused by tissue inhomogeneities and blood flow variations. A series of 915 MHz microstrip array applicators satisfying these criteria have been developed and clinically tested. Clinical and engineering design tradeoffs for practical devices are discussed. Measurements taken in tissue equivalent phantoms and a summary of our clinical experiences with these microstrip arrays are presented.