Allen W. Lohrbach

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

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

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 clinical experiences with these microstrip arrays are presented.<<ETX>>

Hyperthermia and radiation therapy of local-regional recurrent breast cancer: Prognostic factors for response and local control of diffuse or nodular tumors

Over the past decade, hyperthermia has been extensively studied as an adjuvant to radiation therapy in the management of local-regional metastases from adenocarcinoma of the breast. A retrospective review of our experience from July 1982 to January 1990 identified 241 fields in 89 patients which satisfied the following criteria: biopsy confirmation of recurrent or metastatic adenocarcinoma of the breast; involvement of the chest wall and/or regional lymph nodes with diffuse or nodular metastases; treatment which included radiation therapy and externally administered hyperthermia during which mechanically-mapped and/or multipoint normal tissue and intratumoral temperatures were monitored; and at least one follow-up evaluation at 3 weeks or more after completion of treatment. The majority of fields were in patients who had extensive prior treatment including radiation therapy (68%), chemotherapy (86%), and hormonal therapy (58%). Treatment consisted of radiation therapy (average dose: 39.88 Gy) and hyperthermia (1-12 treatments; average 3.12); concurrent chemotherapy or hormonal therapy were also administered in 3% and 32% of the fields, respectively. Parameters characterizing the initial breast cancer, the patient and tumor at the time of hyperthermia, and the treatment were studied in univariate and multivariate analyses with complete response rate at the time of maximum tumor regression and duration of local control as endpoints. The treatments were well tolerated with no life-threatening complications noted. The means for all fields of the mean minimum, mean maximum, and mean average measured intratumoral temperatures were 40.3 degrees C, 44.6 degrees C, and 42.4 degrees C, respectively. At 3 weeks following completion of radiation therapy, response rates were: complete response (52%), partial response (8%), no response (17%), and continuing regression (monotonic regression to less than 50% of initial volume) was noted in 22% of the fields. At the time of maximum tumor regression local control was noted in 72% of the fields. Five parameters correlated with higher complete response in univariate and multivariate analysis: lower T-stage of the initial breast cancer; at the time of hyperthermia age less than 50 years, Karnofsky status greater than 95%, and the absence of distant metastases; and the use of concurrent hormonal therapy. The absence of a family history of breast cancer and concurrent radiation dose greater than or equal to 25 Gy significantly correlated with higher complete response in the univariate but not in the best multivariate models.(ABSTRACT TRUNCATED AT 400 WORDS)

HEATING DEEP SEATED ECCENTRICALLY LOCATED TUMORS WITH AN ANNULAR PHASED ARRAY SYSTEM: A COMPARATIVE CLINICAL STUDY USING TWO ANNULAR ARRAY OPERATING CONFIGURATIONS

Regional heating administered with an annular array to 12 patients with deep-seated advanced malignant disease eccentrically located in the lower abdomen and pelvis is compared based on the annular array operating configuration. One configuration (4 quadrants active) delivers radiofrequency power with relative uniformity throughout the patient cross-section. The other (2 quadrants active) allows the radiofrequency power deposition to be shifted preferentially into the eccentrically located treatment volume. Phantom measurements have been made to demonstrate the redistribution of radiofrequency power that results when the annular array is operated in these respective configurations. Systemic responses (i.e. oral temperature rise, changes in blood pressure, and heart rate) to these regional hyperthermia applications are compared and are not significantly different with respect to these heating configurations. Temperature data obtained during treatment sessions using these two annular array operating configurations are analyzed based on the fraction of measured tumor and normal tissue temperatures exceeding or equal to a given index temperature. Although the two quadrant configuration is more efficient in delivering power to the treatment volume, this analysis does not indicate a significant gain in therapeutic heating as a result of this preferential power deposition. Treatment tolerance and heterogeneity with respect to tissue type and blood flow remained the dominant limiting factors with regard to temperatures achieved.

Interstitial '92ir flexible catheter radiofrequency hyperthermia treatments of head and neck and recurrent pelvic carcinomas

Since September 1983, five patients with head and neck cancers and five patients with pelvic or perineal recurrences of colorectal neoplasms received 192Ir interstitial implants through flexible afterloading catheters that were modified to allow RF hyperthermia treatments of the tumor within 1 hr pre- and post-brachytherapy. Local control in the implant volume was obtained in three of the patients with head and neck cancers (base tongue--2/4; floor of mouth--1/1) with follow-up of 9 to 42 months. Two patients had local recurrences after disease-free periods of 8 and 24 months. Two of the five patients treated for pelvic recurrences had complete responses lasting less than 3 months; prolonged stabilization (12 months) of a presacral mass in a third patient also occurred, but the neoplasm eventually regrew. Average temperatures of 39.2 degrees C to 43.7 degrees C were obtained in the implant volumes of these patients during the 45 minute heating periods which took place prior to loading, and just after removal, of the 192Ir seeds in each patient. No instances of intra or post-operative hemorrhage or necrosis of bone or soft tissues occurred in these patients. However, one individual required a permanent tracheostomy for persistent epiglottic edema after implantation as part of a base-tongue brachytherapy procedure. Interstitial RF hyperthermia in conjunction with brachytherapy appears to be a relatively safe and effective modality, but must be tested prospectively to compare its efficacy to interstitial irradiation alone.

Influence of water bolus temperature on measured skin surface and intradermal temperatures.

Temperature measurements utilizing thermometry probes placed on the skin surface are often used clinically to assess temperatures for the purposes of power control and evaluating treatment efficacy. There is a question, however, as to what extent applicator temperature-controlled liquid coupling boluses can create temperature gradients which can cause significant differences between measurements taken by sensors placed on the skin surface and the actual temperature of the tissue beneath. To address this question, experiments were conducted with human subjects instrumented with surface and shallowly implanted temperature sensors. Microwave applicators with circulating bolus water set at 21 and 41 degrees C were used to induce a temperature gradient in depth in the superficial tissue by thermal conduction. No microwave energy was applied. The average measurement offset at 41 degrees C was 15% of the difference in temperature between the interstitially measured skin temperature and the coupling bolus temperature, towards the temperature of the coupling bolus. The corresponding offset with coupling boluses set near 21 degrees C was 32%. Different water bolus types and volumes were observed to induce different percentage offset errors.

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.

BLADDER COOLING IN PATIENTS TREATED WITH REGIONAL HYPERTHERMIA OF THE PELVIS USING AN ANNULAR PHASED ARRAY

Regional hyperthermia for the treatment of deep seated tumors is often limited by excessive heating of normal tissues, usually with associated patient pain and/or discomfort. The use of bladder cooling via perfusion of distilled water through a modified tri-lumen irrigation catheter as an aid to circumventing this problem in one anatomical region is described. This relatively simple technique provided rapid pain relief and permitted completion of the hyperthermia treatment in a satisfactory manner. Modifications of this technique may permit selective heating and/or cooling of the bladder during regional hyperthermia treatments in the pelvis.