[Present status of hyperthermia in Japan--emphasis on clinical research]

A nationwide survey was conducted by the Japan Society of Hyperthermic Oncology (JSHO) to investigate the present status of hyperthermia in Japan. The results of survey and characteristic clinical research conducted in Japan are described here. 1) In Japan, 185 heating equipment units are in operation at 156 institutes. RF capacitive heating equipment accounts for 60%. 2) Records and registration are complete for 9,000 cases treated by hyperthermia. It is noteworthy that deep-seated tumors account for 60% of the total cases. 3) The percentages of different modalities are as follows: hyperthermia alone, 5.3%; thermoradiotherapy, 57.5%; thermochemotherapy, 22.6%; thermochemoradiotherapy, 14.5%. The present status of hyperthermia is well represented by these percentages. 4) The treatment schedule, indications, and treatment results are almost completely established for a combination of radiotherapy with hyperthermia. 5) Thermochemotherapy is performed at 70% of the surveyed institutes, who expect good treatment results. The JSHO organized a joint research team for thermochemotherapy, and present results are satisfactory. 6) Japan contributes much to the progress of the International Congress of Hyperthermic Oncology. The JSHO presents an ideal environment for research on hyperthermic oncology.

Improved Cartesian coordinate finite difference simulations of small cylindrical objects

An analytical, cylindrical coordinate formula for the thermal resistance around small cylindrical objects has been incorporated into finite difference equations in Cartesian coordinates to improve the accuracy of the numerical simulations of hyperthermia cancer treatments. This is done by introducing a circular finite difference control volume which is centered on the cylindrical object. The temperature distributions calculated from this new formulation and from the formulation obtained from a conventional, rectangular control volume are compared to the predictions from an analytical solution. The results show that for a given Cartesian grid spacing, the new method is superior to the conventional one. This will allow more accurate numerical solutions to be obtained at larger grid spacings when the effect of blood vessels or other cylindrical objects, such as ferromagnetic implants, hot water tubes, etc., are being investigated.

An RF concentrating method using inductive aperture-type applicators

A method for concentrating em energy of a low frequency in hyperthermia is proposed. The phantom together with boli are placed between a pair of inductive aperture-type applicators. The calculated results show that the method can heat the deep portion of the phantom without overheating the fat layers excessively.

Acoustic power calibrations of cylindrical intracavitary ultrasound hyperthermia applicators

Preliminary clinical results indicate that some tumors can be heated well utilizing cylindrical ultrasound sources placed in body cavities. In this paper a simple method for measuring the acoustic power from cylindrical intracavitary transducers will be described. The radially propagating acoustic field was converted to a beam with a single propagation direction by a brass reflector, and the radiation force generated by this beam on an absorbing target was measured. The power output of several clinical intracavitary arrays varied significantly between identically shaped transducer elements. The results show that it is important to measure the acoustic power output from each element prior to its clinical use. The radiation force technique is simple and sensitive and can be easily adapted to be used as a routine clinical quality assurance method.

Benign prostatic hyperplasia: drug and nondrug therapies

Benign prostatic hyperplasia (BPH) is a frequent finding in older men. Patients with symptoms have traditionally been treated with transurethral resection of the prostate, a surgical technique that effectively reduces infravesical obstruction. Nonsurgical management of BPH also has the potential to play an important role in the treatment of patients with moderate or severe symptoms or in those who do not elect surgery. Data are being evaluated to determine the efficacy of treating symptomatic BPH with such modalities as balloon dilation, prostate hyperthermia, androgen suppression, the 5-alpha reductase inhibitor finasteride, and selective alpha blockers.

Thermocouples--the Arizona experience with in-house manufactured probes

The performance of several different types of multisensor thermocouple probes have been tested to determine the feasibility of each type for use in the hyperthermia clinic. All of the probes tested were manufactured in-house, and a detailed description of the construction process will be presented. The overall performance of the probes in terms of robustness, calibration, conduction errors, and response time will be described. In particular, this study describes our experience with in-house manufactured thermocouples over the past several years. The results indicate that when strict quality assurance guidelines are followed, in-house manufactured thermocouples perform satisfactorily--thereby providing an alternative to purchasing probes and measurement systems from commercial vendors if the proper resources are available.

Direct computation of ultrasound phased-array driving signals from a specified temperature distribution for hyperthermia

This paper presents a new method which obtains ultrasound hyperthermia applicator phased-array element driving signals from a desired temperature distribution. The approach combines a technique which computes array element driving signals from focal point locations and intensities with a new technique which calculates focal point locations and power deposition values from temperature requirements. Temperature specifications appear here as upper and lower bounds within the tumor volume, and a focal point placement algorithm chooses focal patterns capable of achieving the temperature range objective. The linear algebraic structure of the method allows rapid calculation of both the phased-array driving signals and an approximate temperature field response. Computer simulations verify the method with a spherical section array (SSA) for a variety of temperature specifications and blood perfusion values. This scheme, which applies to any phased-array geometry, completes an essential step in both treatment planning and feedback for hyperthermia with ultrasound phased-array applicators.

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.

Transurethral microwave thermotherapy for prostatism: early Mayo Foundation experience

As part of a multicenter investigative trial, transurethral microwave thermotherapy of the prostate was used in 60 men with symptomatic benign prostatic hypertrophy. A single office treatment on the Prostatron, a device that provides concurrent microwave heating of the prostate and conductive cooling of the urethra, was well tolerated and caused no major adverse events. Symptomatic improvement, especially the decrease in nocturia and urgency, was dramatic, and urinary flow was improved at 6 weeks. Continued follow-up suggests that further improvement will be achieved and that transurethral microwave thermotherapy has a role in the treatment of benign prostatic hypertrophy.

Equilibrium temperature distributions in uniform phantoms for superficial microwave applicators: implications for temperature-based standards of applicator adequacy

Equilibrium temperature distributions are computed using measured SAR distributions for five different superficial microwave (915 MHz) applicators. We assume a model with uniform conduction and blood flow. A Green's function approach is used to calculate equilibrium solutions which identically obey boundary conditions at the surface of the phantom and at infinite depth. The equilibrium solutions are categorized by surface temperature (TS), maximum allowed temperature (TM), and by a parameter (referred to as the diffusion length, lambda) which characterizes the contributions of thermal conduction relative to blood flow. The computed equilibrium temperature distribution at depths of 2 and 3 cm is strongly dependent on lambda and on TM. It is not strongly dependent on surface temperature for TS below 35 degrees C. In previous work we compared the SAR distribution with local control of 53 superficial tumours with over 1 year of follow-up. As an alternative to an SAR-based description of applicator adequacy we consider a temperature-based standard. Tumours are categorized by the minimum value of lambda that would allow full coverage of the tumour volume by the 42 degrees C contour, assuming a TM of 47.5 degrees C and a TS of 35 degrees C. Eighteen of 27 lesions (67%) were locally controlled for lambda less than 1 cm. The local control in 26 lesions with lambda greater than or equal to 1 cm was 31% (p = 0.016). The lesions with the best results were those with both good coverage in theory (lambda less than 1 cm) and with all monitored catheter tracks achieving at least one session with 30 min at or above 43 degrees C. We found that the temperature-based standard of applicator adequacy was not independent of an SAR-based standard, and in this cohort of patients either a minimum SAR criterion or a maximum diffusion length criterion would serve equally well as a screen for inappropriate applicators.

Isolated limb perfusion for recurrent melanoma of the extremity

Recent reports in the literature suggest that hyperthermic isolated limb perfusion (HILP) may be effective in preventing local recurrence in patients with deeply invasive melanoma or in patients with recurrent disease confined to the extremity. It has been used in the past as an adjuvant treatment after resection of the primary melanoma or recurrence, or as a therapeutic measure if all the disease on the extremity cannot be resected. A prospective, nonrandomized trial of 16 patients with melanoma with recurrent disease confined to the extremity underwent HILP. The protocol involved the wide local excision of all recurrent disease when possible, elective or therapeutic node dissection when indicated, and HILP using cisplatin. In 11 patients in whom all recurrent disease could be resected and the HILP was considered prophylactic, only 1 patient's disease has recurred in the perfusion circuit. Before the perfusion, the 11 patients had a total of 19 local or intransit recurrences. Of the 5 patients in whom all recurrent disease could not be resected, disease persisted in 4 patients. When compared with a concurrent control population of patients with extremity melanoma who had a local recurrence and were not perfused, the patients with melanoma who underwent HILP had a significant prolongation of disease-free survival (p less than 0.05), but a similar actuarial survival. In this study, we demonstrate that HILP can prevent local regional recurrences in patients with metastatic melanoma who are at high risk for further recurrence.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid heating: critical theoretical assessment of thermal gradients found in hyperthermia treatments

There is increasing evidence that many hyperthermia failures are closely related to the large variability of temperatures found in the treatment field. These are linked to thermal gradients near the treatment boundary, vascular perfusion differences, localized cooling, and poor distribution of energy deposition in the tissues. One way of reducing the temperature gradients is to replace traditional heating treatments of 30-60 min by a rapid heating technique, in which the treatment time is a few seconds combined with higher treatment temperatures. The purpose of this paper is to model potential advantages of using various rapid heating protocols, and to compare them with traditional treatments. Theoretical models (in agreement with clinical treatments) suggest that traditional hyperthermia treatments often do not produce the necessary temperature homogeneity needed to kill the last malignant cells in the tumour due to cooler regions in the field. The simulations presented in this paper suggest that much shorter treatment times (1-10 s) should give significant improvements in the treatment field for both the temperature homogeneity and equivalent thermal doses.

RTOG quality assurance guidelines for clinical trials using hyperthermia for deep-seated malignancy

Quality assurance has been vague or lacking in many previous hyperthermia trials. Recent publications by the Hyperthermia Physics Center, the Center for Devices and Regulatory Health, and the Radiation Therapy Oncology Group have described general guidelines for quality assurance in equipment reliability and reproducibility, superficial applications, and microwave techniques. The present report details quality assurance factors that are believed to be important for hyperthermia of deep clinical sites, defined as extending at least 3 cm beyond the skin surface. This document will discuss patient and physician factors, as well as thermometric accuracy, assessment of specific absorption rates (SAR), assurance of adequate coverage of tumors by the energy deposition pattern of the treatment device, and recommended documentation of the location, quantity, and frequency of treatment, specifically oriented to deep hyperthermia. The recommendations are structured to facilitate compliance in multiinstitutional trials.

RTOG quality assurance guidelines for interstitial hyperthermia

This document specifies the current recommendations for quality assurance for hyperthermia administration with interstitial techniques as specified by the Radiation Therapy Oncology Group (RTOG). The document begins by providing a brief description of the physical principles behind the use of the three most commonly used methods of interstitial hyperthermia: radiofrequency (RF-LCF), microwave antennas, and ferromagnetic seeds. Emphasis is placed on features that effect quality assurance. Specific recommendations are provided for: a) Pretreatment planning and equipment performance checks, b) Implant considerations and documentation, c) Thermometry, and d) Safety procedures. Specific details regarding quality assurance issues that are common to all local and regional hyperthermia methods are outlined in previous documents sponsored by the RTOG. It is anticipated that technological advances may lead to future modifications of this document.

Practical experience in electromagnetic hyperthermia quality control procedures within the context of international guidelines

Recent international guidelines on hyperthermia (HT) quality assurance have pointed out the necessity of defining standard operative procedures and technical checks to guarantee an accurate performance of HT treatments. In the present paper, experience is described of quality control procedures that are performed in agreement with the more general guidelines concerning thermometry, sensor positioning, phantoms, applicator characterisation, and electromagnetic (EM) radiation leakage. This practical experience comes from the use of equipment for superficial and loco-regional HT working in the range 13.56-915 MHz.

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.

Hyperthermia: principles and quality assurance

The methods of energy deposition, the power absorbtion properties of biological tissues and the basic components of a typical hyperthermia system are described. In addition, the clinical requirements of hyperthermia treatment are discussed. A perspective on treatment planning and quality control is presented.

Intracavitary hyperthermia: construction and heat patterns of individualized vaginal prototype applicators

Patients who have inoperable or previously irradiated cervical recurrences, especially if very confined and alone, pose a challenging problem to the clinician. Low-dose irradiation and hyperthermia seems to be a promising method for salvage treatments in previously treated patients. In order to heat the vaginal apex, individualized prototype applicators utilizing commercial microwave antennas were constructed and tested in muscle equivalent phantom. The technical construction of vaginal applicators followed Pierquin's procedure for gynaecological brachy-therapy moulds: (1) a true negative vaginal print in alginate was made; (2) a positive mould in plaster of Paris was then constructed; (3) a negative vaginal print was produced in plaster of Paris and (4) heat moulding of a 0.1 cm thick sheet of cellulose acetate on the plaster mould was accomplished. Interstitial microwave antennas were inserted within the applicator and kept in place using silk wires or Teflon rings. The external part of the applicator was thermally sealed and protected with silicone. This was particularly useful in cases where an inner cooling system was required. Heat patterns in tissue equivalent phantom materials were determined using non-perturbing probes and infrared thermography. An illustrative clinical case is described.

Implantable helical coil microwave antenna for interstitial hyperthermia

An implantable helical coil microwave antenna has been developed for improved localization and control of interstitial hyperthermia for deep-seated tumours. A helical coil structure was employed as an extension of the inner conductor at the terminal portion of a miniature semi-rigid coaxial cable. The antennas were constructed with three different connection configurations of the helical coil to the feedline, and with several coil turn densities during the optimization of heating characteristics. In order to compare relative antenna heating performance, a set of quantitative parameters was introduced. Power deposition profiles of 2450 MHz helical coil antennas were studied in both phantom models and muscle tissue in vivo, and compared to those of commonly used dipole antennas. Optimal antenna performance was obtained with a 10-turn per 1 cm helical coil connected to the inner conductor at the tip and separated from the outer conductor by a 0.1 cm gap (HCS-10). These antennas produced a well-localized heating pattern with a sharp falloff of temperature in both directions axially from the coil element. For half-wavelength insertion depths, the effective heating length (50 per cent of maximum SAR) of HCS-10 antennas matched that of standard dipole antennas, but was shifted down towards the tip. For shorter and deeper antenna insertion depths the HCS-10 heating pattern remained similarly localized to the region surrounding the helical coil with minimal cold zone at the tip. In contrast, the dipole antenna heating pattern changed significantly depending on insertion depth, with an unavoidable 0.2-0.7 cm cold region at the antenna tip and elevated surface temperatures for short insertion depths.

Hyperthermia thermometry evaluation: criteria and guidelines

Results of the evaluation of thermometry devices used during hyperthermia treatments at 14 different clinics in the USA are presented. Measurements were made by the Hyperthermia Physics Center (HPC, a national hyperthermia quality assurance program under NCI contract No. N01-CM-37512) according to a protocol. Our sample included thermocouples, fiberoptic thermometers, and high lead resistance thermistors. We found that only some but not all of the thermometers of each kind performed within the +/- 0.2 degrees C acceptability criteria of accuracy. The precision, stability, and response times achieved with each type of thermometer are presented. A summary of perturbations and artifacts typical for each system is presented together with suggested precautions to avoid them during clinical usage. We conclude that although the technology used with each thermometer system is capable of producing a temperature accuracy of 0.2 degrees C, this accuracy is clinically achievable only with a concerted effort and a constant alertness on the part of the investigator. Based on the combined experience of this survey, the clinical investigators we visited, and published reports, we present certain guidelines and procedures that can help to reduce the inaccuracies and improve the reliability of temperature data obtained in clinical hyperthermia trials.

Hyperthermia quality assurance results

The Hyperthermia Physics Center (HPC), under contract with the National Cancer Institute (NCI), has conducted review-type quality assurance (QA) measurements at the five Hyperthermia Equipment Evaluation Centers involved in evaluating the clinical efficacy of a variety of devices for delivering heat treatments to deep-seated human tumours. A summary of the QA protocol, results, testing procedures, standards, criteria, conclusions and recommendations are presented in this paper. The QA review measurements indicate (a) that 81.5 per cent of temperatures surveyed were within the 0.2 degrees C HPC criterion (91 per cent were within 0.4 degrees C), (b) that only 66 per cent of power indications were within the 10 per cent criterion, (c) that the heat patterns in a phantom produced by the BSD Annular Phased Array (AA) had significant variability, (d) that each treatment facility had at least a few potentially occupiable locations where the maximum permissible American National Standards Institute standards of electromagnetic leakage were exceeded, and (e) that these levels of accuracy and safety were achieved only after stringent inhouse QA efforts. From the combined data, it is concluded that the temperature accuracy in this cooperative trial was sufficient to justify a common analysis of clinical data as presented in this series. Also, stringent quality control of every parameter must continue to be stressed in all future hyperthermia trials.

Practical thermal dosimetry

A relatively simple means of thermal dose documentation is presented. It has the advantage of greatly condensing the vast amount of data collected during a course of hyperthermia treatments. The formulation incorporates both temporal and spatial temperature transients and is applicable when comparing hyperthermia devices and in quality control for prospective hyperthermia treatment protocols.