Efficacy of thermotherapy for herpes zoster and postherpetic neuralgia: A protocol for systemic review and meta-analysis

BACKGROUND

Herpes zoster (HZ), is a painful skin rash disease with cutaneous symptoms and acute zoster-associated pain (ZAP). Postherpetic neuralgia (PHN), as the most frequent sequela of HZ, can persist a long time. Both HZ and PHN may significantly impact the quality of life and made great economical afford to affected patients. Its optimal treatment on HZ and PHN is still an urgent problem. In China, thermotherapy, including moxibustion and fire needle, is widely used because they can quickly promote the recovery of shingles and reduce the occurrence of PHN. Thermotherapy can also reduce pain intensity, relieve anxiety, and improve quality of life of PHN. Based on the current literatures, the effect and safety of thermotherapy will be systematically evaluated to provide appropriate complementary therapies for HZ and PHN.

METHODS

Studies search for eligible randomized controlled trials (RCTs) that use thermotherapy including fire needle and moxibustion for HZ or PHN from the following databases: PubMed, EMBASE, Web of Science, the Cochrane Library, China National Knowledge Infrastructure (CNKI), China Biology Medicine Database (CBM), Technology Periodical database (VIP), and Wanfang database. Language restrictions for retrieving literature are English and Chinese. Their data extraction will be done by 2 researchers. Mean difference (MD) or relative risk (RR) with fixed or random effect model in terms of 95% confidence interval (CI) will be adopted for the data synthesis. To evaluate the risk of bias, the Cochrane's risk of bias assessment tool will be utilized. The sensitivity or subgroup analysis will also be conducted when meeting high heterogeneity (I2 > 50%).

RESULTS

This meta-analysis will provide an authentic synthesis of the thermotherapy's effect on HZ and PHN, including incidence of postherpetic neuralgia and adverse events.

DISCUSSION

The findings of the review offer updated evidence and identify whether thermotherapy can be an effective treatment for HZ and PHN for clinicians.

REGISTRATION NUMBER

INPLASY2020110009.

Colorectal peritoneal metastases: Optimal management review

The peritoneum is a common site of dissemination for colorrectal cancer, with a poorer prognosis than other sites of metastases. In the last two decades, it has been considered as a locoregional disease progression and treated as such with curative intention treatments. Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) is the actual reference treatment for these patients as better survival results have been reached as compared to systemic chemotherapy alone, but its therapeutic efficacy is still under debate. Actual guidelines recommend that the management of colorectal cancer with peritoneal metastases should be led by a multidisciplinary team carried out in experienced centers and consider CRS + HIPEC for selected patients. Accumulative evidence in the last three years suggests that this is a curative treatment that may improve patients disease-free survival, decrease the risk of recurrence, and does not increase the risk of treatment-related mortality. In this review we aim to gather the latest results from referral centers and opinions from experts about the effectiveness and feasibility of CRS + HIPEC for treating peritoneal disease from colorectal malignancies.

The potential of constrained SAR focusing for hyperthermia treatment planning: analysis for the head & neck region

Clinical trials have shown that hyperthermia is a potent adjuvant to conventional cancer treatments, but the temperatures currently achieved in the clinic are still suboptimal. Hyperthermia treatment planning simulations have potential to improve the heating profile of phased-array applicators. An important open challenge is the development of an effective optimization procedure that enables uniform heating of the target region while keeping temperature below a threshold in healthy tissues. In this work, we analyzed the effectiveness and efficiency of a recently proposed optimization approach, i.e. focusing via constrained power optimization (FOCO), using 3D simulations of twelve clinical patient specific models. FOCO performance was compared against a clinically used particle swarm based optimization approach. Evaluation metrics were target coverage at the 25% iso-SAR level, target hotspot quotient, median target temperature (T50) and computational requirements. Our results show that, on average, constrained power focusing performs slightly better than the clinical benchmark ([Formula: see text]T50 [Formula: see text] °C), but outperforms this clinical benchmark for large target volumes ([Formula: see text]40 cm[Formula: see text], [Formula: see text]T50 [Formula: see text] °C). In addition, the results are achieved in a shorter time ([Formula: see text]%) and are repeatable because the approach is formulated as a convex optimization problem.

Treatment of cutaneous leishmaniasis with thermotherapy in Brazil: an efficacy and safety study

BACKGROUND

Pentavalent antimonials remain as the standard drugs in the treatment of cutaneous leishmaniosis. The high cost, difficult administration, long treatment time, toxicity and increasing morbidity are factors that limit the use of these drugs.

OBJECTIVES

To describe the response to radiofrequency thermotherapy in the treatment of localized cutaneous leishmaniasis in Brazil, and to evaluate its safety and tolerability.

METHODS

We conducted a non-comparative open trial with a total of 15 patients confirmed to have cutaneous leishmaniasis on parasitological examination. A single radiofrequency thermotherapy session at 50ºC for 30 seconds was applied to the lesion and its edges. In patients with more than one lesion, only the largest one was treated initially. If after 30 days there was no evidence of healing, the smaller lesion was also treated with thermotherapy. Clinical cure was defined as visible healing for three months after treatment. The patients were followed-up for six months and there was no follow-up loss.

RESULTS

Of all 23 lesions, only two evolved to complete healing without the need of treatment. Of 21 lesions, 18 (85.7%) achieved full healing. The main observed side effects were itching, burning sensation, pain and blisters.

STUDY LIMITATIONS

Sample with a small number of patients and short follow-up.

CONCLUSION

Thermotherapy can be considered a therapeutic alternative in localized cutaneous leishmaniasis, especially in cases of single cutaneous lesions and with formal contraindications to conventional treatment with pentavalent antimonials.

[Comparative experimental study of morphological and histochemical changes of chorioretinal complex after subthreshold laser exposure]

The influence of several subthreshold laser procedures on chorioretinal complex (CRC) tissues was experimentally studied in rabbits using histological and histochemical methods. Subthreshold micropulse laser radiation and transpupillar thermotherapy were found to have the most attenuated and advantageous effect on CRC structure. The feature of subthreshold laser exposure is partly reversible selective changes in CRC, that have temporary stimulating effect on cellular metabolism and local regenerative processes providing an opportunity for still viable tissues to function adequately.

Transient solution to the bioheat equation and optimization for magnetic fluid hyperthermia treatment

Two finite concentric spherical regions were considered as the tissue model for magnetic fluid hyperthermia treatment. The inner sphere represents the diseased tissue containing magnetic particles that generate heat when an alternating magnetic field is applied. The outer sphere represents the healthy tissue. Blood perfusion effects are included in both the regions. Analytical and numerical solutions of the one-dimensional bioheat transfer equation were obtained with constant and spatially varying heat generation in the inner sphere. The numerical solution was found to be in good agreement with the analytical solution. In an ideal hyperthermia treatment, all the diseased tissues should be selectively heated without affecting any healthy tissue. The present work optimized the magnetic particle concentration in an attempt to achieve the ideal hyperthermia conditions. It was found that, for a fixed amount of magnetic particles, optimizing the magnetic particle distribution in the diseased tissue can significantly enhance the therapeutic temperature levels in the diseased tissue while maintaining the same level of heating in the healthy tissue.

Leg coverage with towels during regional deep hyperthermia treatment and its effect on pelvic temperature and temperature distribution

INTRODUCTION

The feasibility and its effects on pelvic temperature distribution of covering the legs with towels during the second half of the deep hyperthermia treatment (DHT) is evaluated.

PATIENTS AND METHODS

Patients treated with DHT and radiotherapy were randomized to an alternating treatment schedule: 2nd and 4th treatment or 3rd and 5th treatment with the legs covered with towels in the second half of the treatment. Intra-luminal temperatures (vesical, vaginal and rectal) classified as tumour indicative (TI) or tumour contact (TC), oral temperature, applied maximum power and power at the end of the treatment were measured and compared between the two treatment schedules.

RESULTS

Fourteen female patients receiving a total of 51 treatments, 24 with and 27 without towels, were included for analysis. The mean intra-luminal, TI and TC temperatures, standard deviation and range for each site were calculated. The applied power was documented. There were no significant differences in any of the measured temperatures. There were no significant differences in the applied power. In only three treatments, the towels were removed preliminarily.

CONCLUSION

In the authors' experience, covering the legs with towels during the second half of DHT does not result in significantly higher or more homogeneous pelvic temperatures. There is no indication that the TC and TI temperatures are higher compared to all pelvic temperatures when towels are applied. Regarding the used power, there is no significant decrease with towels placed on the legs. Coverage of the legs does not increase the systemic temperature. Isolating the legs with a water-perfused heater is considered.

A forward model and conjugate gradient inversion technique for low-frequency ultrasonic imaging

Emerging methods of hyperthermia cancer treatment require noninvasive temperature monitoring, and ultrasonic techniques show promise in this regard. Various tomographic algorithms are available that reconstruct sound speed or contrast profiles, which can be related to temperature distribution. The requirement of a high enough frequency for adequate spatial resolution and a low enough frequency for adequate tissue penetration is a difficult compromise. In this study, the feasibility of using low frequency ultrasound for imaging and temperature monitoring was investigated. The transient probing wave field had a bandwidth spanning the frequency range 2.5-320.5 kHz. The results from a forward model which computed the propagation and scattering of low-frequency acoustic pressure and velocity wave fields were used to compare three imaging methods formulated within the Born approximation, representing two main types of reconstruction. The first uses Fourier techniques to reconstruct sound-speed profiles from projection or Radon data based on optical ray theory, seen as an asymptotical limit for comparison. The second uses backpropagation and conjugate gradient inversion methods based on acoustical wave theory. The results show that the accuracy in localization was 2.5 mm or better when using low frequencies and the conjugate gradient inversion scheme, which could be used for temperature monitoring.

Temperature data analysis for 22 patients with advanced cervical carcinoma treated in Rotterdam using radiotherapy, hyperthermia and chemotherapy: a reference point is needed

INTRODUCTION

The growing interest and participation in multi-institutional trials involving deep hyperthermia treatment is an important step towards the further consolidation of hyperthermia as an oncological treatment modality. However, the differences in the clinical procedures of hyperthermia application also raises questions as how to compare the reported temperatures data obtained by the different institutes. In this study our recent developed approach, RHyThM (Rotterdam Hyperthermia Thermal Modulator), has been used for thermal data analysis to investigate the temperature dynamics behaviour of a series of deep hyperthermia treatments.

PATIENTS AND METHODS

All 22 patients (104 hyperthermia treatments) with locally advanced cervical carcinoma who participated in a feasibility study for treatment with a three-modality therapy were selected. The patients received mega-voltage external beam radiotherapy to the pelvis in daily fractions of 2 Gy five times a week to a total dose of 46 Gy and additional brachytherapy, at least four courses of weekly cisplatin (40 mg m-2) and five sessions of weekly loco regional deep hyperthermia treatments with the BSD2000-3D with the Sigma 60 or the Sigma-eye applicators at frequencies 70-120 MHz. Using RHyThM tissue type was defined along the insertion length, based on the CT scan information in radiotherapy position, for each single treatment. A step change in the slope of the profile of the first temperature map was identified to verify the insertion length of the thermometry catheter and precise location of the transition between in- and outside the body. Data analysis was performed based on the temperature readout provided by RHyThM.

RESULTS

The temperature and RF-power data of 97 treatments could be analysed. The intra-vaginal temperature indices were slightly lower than those for bladder and rectum. The average T50 (median temperature) in all lumens, i.e. bladder, vagina and rectum, was 40.4 +/- 0.6 degrees Celsius. The average vagina all lumen T50 was 40.0 +/- 0.8 degrees Celsius. The average bladder and rectum all lumen T50 was 40.6 +/- 0.7 degrees Celsius and 40.5 +/- 0.6, respectively. When the analysis was restricted to the deepest 5 cm of the vagina lumen, the average T50 was 39.8 +/- 0.9 degrees Celsius. Good correlation exists between the various temperature indices like T20, T50 and T90, for all lumen measurements in bladder, vagina and rectum. No correlation was found between temperature indices and treatment number. For the complete patient population, no relationship was found between T50 and net integrated RF-power applied. In an explorative analysis on individual patients a positive correlation coefficient or trend was found in 14 patients between normalized net integrated RF-power and vagina T50.

CONCLUSION

Average all lumen T50 for bladder, vagina and rectum differ less than 1 degrees Celsius, indicating that a large volume was heated relatively homogeneously. The vagina T50 value depends on how many measurement points are included for the analysis. In this group of patients the vagina T50 of the first treatment is not a good measure to discriminate between patients with 'heatable' and 'non-heatable' tumours. In order to compare temperature data reported by different institutes dealing with the same group of patients, one needs a strict and clear agreement on which temperature measurements or reference point(s) that should be included in the analysis.

A thermometry system for quality assurance and documentation of whole body hyperthermia procedures

Since December 2001, the Department of Oncology and Medical Physics, Haukeland University Hospital, Norway has been conducting whole body hyperthermia (WBH) studies, treating patients with either ovarian carcinoma or non-Hodgkin lymphomas. Accurate and reliable thermometry instrumentation is important in all types of hyperthermia procedures, particularly in WBH, where the target patient body temperature is 41.8 degrees C. Reliable documentation of side-effects in clinical studies is also dependent on precise temperature monitoring, since in this temperature range even small, but systematic, inaccuracies (0.1-0.2 degrees C) in the temperature monitoring is expected to affect the amount of side effects. Readily available heating and temperature data from previous treatment sessions of the same patient is also valuable for precise temperature control in future treatment sessions. The WBH thermometry system implemented at Haukeland University Hospital is described. It is based on commercially available components, including standard medical thermistor probes, and includes a temperature calibration and verification facility. The thermometry system is accurate, reliable, easy to use, comfortable for the patient and relatively inexpensive. By implementing the Steinhart-Hart polynomial fit to standard medical thermistor probe data, it is shown that the WBH treatment thermometers used can measure the patient body temperatures with a short- and long-term accuracy of +/- 0.01 degrees C.

[Standards and perspectives in locoregional hyperthermia]

The term "hyperthermia" summarises different procedures of raising the temperature of a tumour-loaded tissue to a temperature of 40-43 degrees C. In this context, locoregional procedures (radiative/capacitive local, interstitial and regional hyperthermia; endoluminal hyperthermia), hyperthermic perfusion techniques (hyperthermic peritoneal and isolated limb perfusion), and whole-body hyperthermia differ with regard to their indication, expenditure of application, and evidence of efficacy. All hyperthermia techniques have in common that they have no sufficient antineoplastic activity alone in the temperature range below 43-45 degrees C, but act in a synergistic way with radiotherapy and certain cytotoxic drugs. 14 out of 18 published randomised trials on hyperthermia as an adjunct to standard radio- or chemotherapy refer to locoregional approaches. Particular progress has been made in regional radiofrequency hyperthermia, where novel multiantenna-applicators and their integration into MR-applicators ("hybrid-systems") have recently been introduced into clinical practice. In addition, combinations of hyperthermia with novel technologies (magnetic fluid hyperthermia, thermosensitive liposomes, immunotherapy, gene targeting) are imminent. We here give a critical update on the proven indications of the different locoregional hyperthermia approaches and on the current clinical and technological progress in this field.

Characterization of the SAR-distribution of the Sigma-60 applicator for regional hyperthermia using a Schottky diode sheet

INTRODUCTION

Characterization of the performance of an hyperthermia applicator by phantom experiments is an essential aspect of quality assurance in hyperthermia. The objective of this study was to quantitatively characterize the energy distribution of the Sigma-60 applicator of the BSD2000 phased array system operated within the normal frequency range of 70-120 MHz. Additionally, the accuracy of the flexible Schottky diode sheet to measure E-field distributions was assessed.

MATERIAL AND METHODS

The flexible Schottky diode sheet (SDS) consists of 64 diodes mounted on a flexible 125 microm thick polyester foil. The diodes are connected through high resistive wires to the electronic readout system. With the SDS E-field distributions were measured with a resolution of 2.5 x 2.5 cm in a cylindrical phantom, diameter of 26 cm and filled with saline water (2 g/l). The phantom was positioned symmetrically in the Sigma-60 applicator. RF-power was applied to the 4-channel applicator with increasing steps from 25W to a total output of 400 W.

RESULTS

The complete system to measure the E-field distribution worked fine and reliably within the Sigma-60 applicator. The E-field distributions measured showed that the longitudinal length of the E-field distribution is more or less constant, e.g. 21-19 cm, over the frequency range of 70-120 MHz, respectively. As expected, the radial E-field distributions show a better focusing towards the centre of the phantom for higher frequencies, e.g. from 15.3-8.7 cm diameter for 70-120 MHz, respectively. The focusing target could be moved accurately from the left to the right side of the phantom. Further it was found that the sensitivity variation of nine diodes located at the centre of the phantom was very small, e.g. < 3% over the whole frequency range.

CONCLUSION

The SAR distributions of the Sigma-60 applicator are in good agreement with theoretically expected values. The flexible Schottky diode sheet proves to be an excellent tool to make accurate, quantitative measurements of E-field distributions at low (25 W) and medium (400 W) power levels. An important feature of the SDS is that it enables one to significantly improve quantitative quality assurance procedures and to start quantitative comparisons of the performance of the different deep hyperthermia systems used by the various hyperthermia groups.

Image-guided tumor ablation: proposal for standardization of terms and reporting criteria

The field of image-guided tumor ablation requires standardization of terms and reporting criteria to facilitate effective communication of ideas and appropriate comparison between treatments with different technologies, such as chemical ablation (ethanol or acetic acid) and thermal therapies, such as radiofrequency, laser, microwave, ultrasound, and cryoablation. On the basis of this premise, a working committee was established with the goal of producing a proposal on such standardization. The intent of the Working Group is to provide a framework that will facilitate the clearest communication between investigators and will provide the greatest flexibility in comparisons between the many new, exciting, and emerging technologies. The members of the Working Group now propose a vehicle for reporting the various aspects of image-guided ablation therapy, including classifications of therapies and procedures, appropriate descriptors of image guidance, and terms to define imaging and pathologic findings. Methods for standardizing the reporting of follow-up findings and complications and other important aspects that require attention when reporting clinical results are addressed. It is the group's hope and intention that adherence to the recommendations of this proposal will facilitate achievement of the group's main objective: improved precision and communication in this field that lead to more accurate comparison of technologies and results and ultimately to improved patient outcomes.

Stability and accuracy of power and phase measurements of a VVM system designed for online quality control of the BSD-2000 (-3D) DHT system

Accurate control of power and phase is essential for the quality assurance of hyperthermia treatments. Hereto, an external measurement device was inserted, built around a Vector Voltmeter (VVM), in order to assess online the performance of the steering capability of the BSD-2000 and later the BSD-2000-3D system. This paper only concerns the power and phase calibration of the signal in the path between the power and phase detection probes of the BSD-system and power and phase measurement point of the VVM. The calibration is performed in the frequency range of 60-120 MHz using a network analyser with a frequency range of 0.01-500 MHz. More importantly, by repeating the calibration periodically over the last 3 years, the stability and accuracy of the power and phase measurements were determined using the VVM system. The results of the power calibration show that the VVM system, concerning its power and phase measurement, is stable in time. The variation of the power measured with the VVM system is less than 0.22 dB (5.2%) for the latest configuration of the BSD-2000-3D system. The variation of the VVM-based phase measurements of the latter configurations is 1.1 degrees or less. From the results of the power and phase measurements in the BSD 2000 system reported in previous studies using other measurement systems, it follows that the uncertainties of the power and phase measurements with the currently proposed VVM system are small enough to assess accurately the performance of the BSD system concerning its steering capability.

Transurethral interstitial laser coagulation of the prostate and transurethral microwave thermotherapy vs transurethral resection or incision of the prostate: results of a randomized, controlled study in patients with symptomatic benign prostatic hyperplasia

OBJECTIVE

To compare the efficacy and frequency of complications of transurethral interstitial laser coagulation (ILC) and transurethral microwave thermotherapy (TUMT) with transurethral resection or incision of the prostate (TURP/TUIP) in patients with symptomatic benign prostatic hyperplasia (BPH).

PATIENTS AND METHODS

Forty-eight patients were randomized to undergo ILC, 46 to TUMT and 24 to TURP/TUIP; they were followed for 6 months and the outcome analysed on an intention-to-treat basis.

RESULTS

At 6 months the symptom scores and maximum urinary flow rate (Qmax) had improved significantly in all groups. At 6 months the mean symptom score was 9.2 in both experimental groups and 6.8 in the control group (P > 0.05); the mean Qmax was 20.6 mL/s in the control group, 16.2 in the ILC group (P > 0.05 vs control) and 13.2 in the TUMT group (P < 0.05 vs. the control group). In the TUMT group patients developing urinary retention afterward had a significantly greater increase in Qmax than those who did not. The types of complications in the three groups varied. Urinary tract infection occurred frequently in the experimental groups, especially after ILC, whereas the 'well-known' complications of TURP occurred in the control group. Overall, 36% in the ILC, 54% in the TUMT and 73% in the control group had no complications (retrograde ejaculation excluded) during the first 6 months. One patient in the TUMT group underwent TURP after 3 months, whereas no patients in the ILC or the con-trol group were re-treated for BPH within the first 6 months.

CONCLUSION

In the short term both ILC and TUMT are reasonable alternatives to standard transurethral surgery for symptomatic BPH, where the reduction of symptoms is the primary goal of treatment. However, both ILC and TUMT were associated with morbidity, although the complication profiles differed from those after TURP/TUIP. Both ILC and TUMT seem advantageous in some patients because of the reduced risk of bleeding and the eliminated risk of TUR syndrome, and because TUMT only requires local anaesthesia. Thus, as neither treatment is better in all aspects, the advantages of one technique over the other must be weighed when deciding how to treat each patient.

[Measures of specific absorption rate (SAR) in microwave hyperthermic oncology and the influence of the dynamic bolus on clinical practice]

AIM

The bolus (silicon + deionized water) is used in order to achieve a good electromagnetic match between the biological tissue and the applicator surface and to locally modify the skin temperature, to regulate it based on the patient's sensitivity. Therefore, it is very important to know the electromagnetic power deposition and how the bolus can induce a variation in the thermal map, both superficially and deeply. The aim of this study is to evaluate the applicator characteristics in the same conditions as those indicated by the ESHO guidelines for clinical practice and to investigate the penetration depth in the absence and in the presence of a very effective circulating bolus. The first condition is used by the manufacturer to characterize MW applicator while the second condition is used by medical equipes delivering HT treatments.

MATERIAL AND METHODS

The specific absorption rate (SAR) generated by a microwave planar applicator (H2, CFMA, Istok,Russia) operating at 433 MHz connected with the hyperthermic equipment ALBA (Restek, Italy) was studied in a muscle-equivalent polyacrilamide phantom. IsoSAR lines were detected on a liquid crystal sheet with a video camera. Images analysis was performed using the graphic software Paint Shop Pro 6. This method allows to evaluate PD in the phantom under the plane of MW applicator. The hyperthermic equipment ALBA is used in the Radiotherapy Unit of the Mauriziano Umberto I Hospital in Turin for both oncologic and psychiatric treatments.

RESULTS AND DISCUSSION

The actual pattern of measured SAR mainly depends on the applicator and the phantom characteristics, but also the thickness and the efficiency of the bolus inserted between the applicator and the patient's skin have been shown to affect the results. In this study the penetration depth was measured on 5 applicator sections both with non circulating bolus (static) and with circulating bolus (dynamic). The penetration depth is reduced with the dynamic bolus with respect to the static bolus in all sections, and specifically: in section I it is reduced from 19.46 +/- 1.49 mm to 17.22 +/- 0.71 mm; in section II from 38.17 +/- 4.77 mm to 26.91 +/- 1.48 mm; in section III from 39.81 +/- 3.24 mm to 30.38+/- 4.56 mm; in section IV from 42.12 +/- 1.67 mm to 33.11 +/- 1.89 mm; and finally in section V from 39.83 +/- 4.14 mm to 31.064 +/- 1.57 mm. The above reduction ranges between 11.5 and 29 % with an average value of 21.64 % Our results suggest that different conditions at the interface between bolus and phantom resulting from the use of a dynamic or static bolus produce considerable changes on the heated volume dimension and on the SAR local pattern. The effect of the convective heat losses due to the circulating bolus' assessed by our measurements is not negligible and should be taken into account when evaluating the SAR distribution before clinical treatments.

CONCLUSIONS

To disregard the heat losses due to a circulating bolus in MW applicator characterization can severely affect the SAR estimation. This may have serious consequences on clinical applications, since the temperature in the heated lesion can be lower than expected, and the clinical effectiveness of the therapeutical session can be therefore severely reduced. Since at the moment inexpensive and accurate non-invasive temperature monitoring systems are not available, a sound knowledge of the PD of the MW applicator is of primary importance for clinical applications and for a treatment plan allowing to deliver customized treatment to each patient.

Evaluation of thermal therapy in a prostate cancer model using a wet electrode radiofrequency probe

PURPOSE

To determine the temperature-time threshold of local cell death in vivo for thermal therapy in a prostate cancer animal model and to use this value as a benchmark to quantify global tissue injury.

MATERIALS AND METHODS

Two studies were designed in the Dunning AT-1 rat prostate tumor hind limb model. For both studies, a wet electrode radiofrequency (RF) probe was used to deliver 40 W of energy for 18 to 62 seconds after a 30-second infusion of hypertonic saline/Hypaque through the RF antenna. Thermal history measurements were obtained in tumors from at least two Fluoroptic probes placed radially 5 mm from the axis of a RF probe and 10 mm below the surface of the tissue. In study 1, the thermal history required for irreversible cell injury was experimentally determined by comparing the predicted injury accumulation (omega) with cell viability at the fluoroptic probe locations using an in vivo-in vitro assay. The omega value was calculated from the measured thermal histories using an Arrhenius damage model. In study 2, RF energy was applied for 40 seconds in all cases. At 1, 3, and 7 days after thermal therapy, triphenyltetrazolium chloride dye (TTC) and histologic analyses were performed to assess global tissue injury within a 5-mm radius from the axis of the RF probe.

RESULTS

Study 1 showed that cell survival dropped to 0 for 0.42 < omega < 0.7. This result was the basis for selection of 40 seconds of RF thermal therapy in study 2, which yielded omegaave = 0.5 in the tissue 5 mm from the probe axis. Both TTC and histology analysis showed that sham-treated tissue was not irreversibly injured. However, there was an inherent heterogeneity present in the tumor that accounted for as much as 15% necrosis in control or sham-treated tissue. In contrast, at 1, 3, and 7 days after therapy, significantly less enzyme activity was observed by TCC in thermally treated tissue compared with sham-treated tissue (35 v 85%; P < 0.001). Histologic analysis of thermally treated tissues revealed a gradual increase in the percent of coagulative necrosis (47%-70%) with a concomitant decrease in the percentage of shocked cells (53%-28%). At day 7, <3% viability was observed in treated tumors compared with 90% viability in sham-treated tissue.

CONCLUSION

The threshold of cellular injury in vivo corresponded to omega > 0.7 (> or =48 degrees C for 40 seconds). Global tissue injury could be conservatively predicted on the basis of local thermal histories during therapy.

Long-term local intensive preoperative chemotherapy and joint-preserving conservative surgery for osteosarcoma around the knee

This study evaluated conservative joint-sparing surgery for patients with osteosarcoma around the knee. Of 23 patients with stage IIB osteosarcoma around the knee, 5 were treated with long-term (30-56 weeks) local intensive preoperative chemotherapy consisting of high-dose methotrexate, intra-arterial and intravenous cisplatinum, doxorubicin, and hyperthermic isolated regional perfusion. More conservative resection, sparing the knee joint, was performed with smaller sufficient surgical margin in these 5 patients, preserving good limb function. Excellent local effects were achieved in the resected specimens. These results suggest long-term local intensive preoperative chemotherapy, including intra-arterial cisplatin and hyperthermic isolated regional perfusion, help control local tumor and allow for more conservative surgery.

Transurethral microwave thermotherapy: an alternative to medical management in patients with benign prostatic hyperplasia?

Transurethral microwave thermotherapy (TUMT) is being increasingly considered as an alternative to medical management with alpha-blockers or finasteride in patients with lower urinary tract symptoms (LUTS) of benign prostate hyperplasia (BPH). Enduring clinical benefits have been demonstrated after a single 1-hour microwave treatment session under topical anesthesia, and the associated morbidity is low. Optimal results are obtained with the delivery of high thermal doses and accurate targeting of microwave energy. Extensive evidence from randomized clinical trials supports the safety and efficacy of both microwave treatment and medical management, but randomized trial data have only recently become available directly comparing these two approaches to BPH treatment. These data indicate that greater long-term improvements in symptoms, peak urinary flow rates, and quality of life are attained with microwave treatment than with alpha-blockade. Furthermore, the actuarial rate of treatment failure is markedly lower in patients undergoing microwave v alpha-blocker treatment. However, the onset of action of alpha-blocker treatment is more rapid. The principal limitations of alpha-blockade are side effects and lack of efficacy leading to treatment failure in some patients. The maximal effects of finasteride are modest and require a period of months to be manifested, although the side effect profile and tolerability of this agent are favorable. Neoadjuvant and adjuvant alpha-blocker therapy can accelerate symptom and flow rate improvement after TUMT. In contrast to medical management, microwave treatment is highly versatile, allowing patients over a broad range of baseline symptom severities and prostate sizes to be treated with a high probability of success.

Clinical results of microwave thermotherapy for benign prostatic hyperplasia

Transurethral microwave thermotherapy is a truly office procedure without the need for anesthesia for the treatment of lower urinary tract symptoms caused by benign prostatic hyperplasia. Several devices have been developed. Continuous refinement of the procedure led to higher energy protocols and high-intensity dose protocols applying the heat-shock strategy. We report on the clinical results of these protocols. Symptom scores improve around 60%, whereas maximum urinary flow rate improve from an average 9 to 10 mL/sec at baseline to 14 to 15 mL/sec during follow-up. No significant differences have been shown between the outcomes with the different devices. Long-term data show satisfactory results after 4 years. Initial clinical results with the heat-shock strategy show results comparable to those of higher-energy protocols with decreased morbidity. Treatment morbidity of higher energy protocols is moderate and consists mainly of the need for catheterization and a higher percentage of retrograde ejaculation. To improve treatment efficacy, patient selection appears to be most important. Prostate size, bladder outlet obstruction, age, and prostate composition are of predictive value for treatment outcome. Further development of the treatment protocols and refinement of the urethral applicators might enhance outcome.

Durability of results obtained with transurethral microwave thermotherapy in the treatment of men with symptomatic benign prostatic hyperplasia

To assess the durability of the results of transurethral microwave thermotherapy (TUMT) for symptomatic benign prostatic hyperplasia (BPH), we have reviewed publications describing trials with at least 3 years of follow-up. For men treated only by TUMT, improvement in symptoms and quality of life appears to be maintained for at least 4 to 5 years. Improvement in peak flow rates is modest but is generally maintained, particularly after higher-energy therapies. These results represent responders, and a crucial question is the need for additional treatments. With lower-energy treatment, this is common: between 50% and 60% within 3 to 5 years. With higher-energy TUMT, the retreatment rate appears to be less, approximating 20% within 3 to 4 years. When comparing these results with those of transurethral resection, it should be noted that there is a significant failure rate with surgery, and even if failure is more common with TUMT, men may be prepared to accept this risk rather than the greater morbidity of prostatectomy.

An on-line phase measurement system for quality assurance of the BSD 2000. Part II: results of the phase measurement system

Phase constancy and accuracy are significant for regional hyperthermia with phased array radiofrequency hyperthermia systems. They are both necessary for a precise target steering in therapy. For the BSD 2000 system (BSD Medical Corp. Salt Lake City, Utah, USA), the phase values of all channels are checked with a self-developed automatic on-line phase measurement system. On different days the phases are measured under identical conditions, where the output paths are cut off with 50 ohm dummy loads to suppress the influence of the radiation conditions of the antennae on the measurement values. The results show how the phase values of the four channels change in the first 30 min and from day to day. During this time interval after the start the phases drop down by up to 15 degrees. For the time later changes are very slight and the differences from day to day are negligible. The phase shift that occurs in the first 30 min is as high as a change of the target point by 1 cm. Earlier switching on of the amplifiers prevents this shift occurring during the treatment. The measurement system provides a good tool for determination of phase accuracy and is easy to realize.

An on-line phase measurement system for quality assurance of the BSD 2000. Part I: technical description of the measurement system

The hyperthermia system BSD 2000 with the ring applicator Sigma 60 utilizes the principle of a phase controlled group radiation source. The accuracy of the phase relationship between the four receiving HF signals is crucial for the position of the electric field inside the applicator. Therefore, essential significance falls to the phase control of the system. An automatic phase measuring technique has been developed to register immediately the phase position of the four channels of the BSD 2000 with respect to a reference signal. The system improves the insurance of the technical safeguarding. In the first part of this work, the technical realization of the measurement system is described and first measurements with the system are given. In the second part, results with respect to the quality assurance of the BSD 2000 system are presented.

Validation of MR thermometry technology: a small animal model for hyperthermic treatment of tumours

BACKGROUND

Local hyperthermia has been shown to be an effective adjuvant therapy for cancer. However, progress in this treatment modality requires the non-invasive assessment of temperature distribution in the entire tumour to enable administration of an efficient thermal dose to all tumour areas. Magnetic resonance (MR) imaging offers a promising tool to quantify, non-invasively and three-dimensionally, temperature distribution within tumours. An animal model taking into account the complex interrelationship between pathophysiological changes within a tumour during hyperthermia and temperature-sensitive MR parameters is warranted for the development and validation of new MR thermometry technology.

METHODS

An experimental set-up was implemented to allow simultaneous measurements of temperature, tumour blood flow and temperature-sensitive MR parameters under standardised conditions in vivo. Local hyperthermia was induced at 44 degrees C for 20 min under inhalation anaesthesia on seven Syrian Golden hamsters bearing an amelanotic melanoma. Fibreoptic probes were used for reference temperature measurements. Laser Doppler flowmetry served for on-line tumour blood flow determination, and MR thermometry was performed using longitudinal T1 relaxation time measurements.

RESULTS

The experimental design enables multifunctional MR thermometry. T1 relaxation times of tumours were 1.44 s (1.36, 1.46) and 1.53 s (1. 48, 1.75) at 37 degrees C and during hyperthermia at 44 degrees C, respectively (median, 25% and 75% quartiles, respectively; P<0.05). At the end of 20 min of hyperthermic treatment at 44 degrees C, relative tumour blood flow was reduced to 40.5% (20.7, 43.3) compared to values before treatment (median, 25% and 75% quartiles, respectively; P<0.05). Imaging of T1 relaxation times revealed a heterogeneous distribution in temperature during hyperthermic treatment.

CONCLUSION

This novel in vivo model allows standardised investigations for the development and validation of MR thermography methods.

[Research and development called for thermotherapy of prostatic hyperplasia]

Symptomatic benign prostatic hyperplasia is to be considered an endemic disease, and the treatment of these problems of elderly men constitutes a substantial drain on health care resources. Transurethral microwave thermotherapy (TUMT) is one of many new treatment methods introduced in Sweden since the beginning of the decade. The article consists in a review of results obtained with TUMT, and discussion of further development of the technique at present under way in this country.

[Thermotherapy in rheumatic diseases]

Heat and cold treatment are often used in the physical therapy of rheumatic diseases. Thermotherapy influences perfusion, muscular tone, pain, and inflamed arthritic joints. Cold applications are preferable in treating active arthritis. Heat treatment is advantageous in the management of less active arthritis and non-inflammatory rheumatic disorders. Current investigations demonstrate that thermotherapy influences the endocrine--an immune systems.

Increased heating efficiency of hyperthermia using an ultrasound contrast agent: a phantom study

It is known that there are large temperature elevations in proximity to air bubbles during US (ultrasound) heating. The existence of tiny air bubbles in the target tissue may enhance the temperature elevation in US hyperthermia. To examine this hypothesis, phantom tissue experiments using an US contrast agent consisting of tiny air bubbles surrounded by a 5% (w/v) human albumin shell (Alb) were performed. As a phantom tissue, a 2 cm cube of beef was used. The phantom tissue was heated with or without the US contrast agent by an US hyperthermia device for 3 min. The heating device was operated at 1.5 MHz with the US intensity of 0.9 W/cm2. Physiological saline solution, iodized oil, and ethanol were used for control experiments. The effect of multiple needle punctures to the beef phantom was also examined. The temperature elevation rate (TER) was defined as the ratio of temperature elevation by heating with Alb or control materials to the temperature elevation by US heating alone. The TER of Alb was 1.7, whereas the TERs of the control materials and of the multiple needle punctures were approximately 1. The administration of Alb significantly increased the temperature in US hyperthermia. In addition, the heating efficiency of Alb was compared to the effect of an increase in the US intensity. Phantom tissue was heated at various US intensities. When the US intensity was increased from 0.9 to 1.8 W/cm2, the temperature elevated by approximately 1.7-fold. Thus, the effect of the administration of Alb was almost equivalent to the effect of increase in US power intensities from 0.9 to 1.8 W/cm2 in the present experimental settings. The results suggest that the US contrast agent can be a potential enhancer in US hyperthermia.

ESHO quality assurance guidelines for regional hyperthermia

The Technical Committee and the Clinical Committee of the ESHO evaluated the experience of the institutes which are active in clinical regional hyperthermia using radiative equipment. Based on this evaluation, QA guidelines have been formulated. The focus of these guidelines lies on what must be done not on how it should be done. Subjects covered are: treatment planning, treatment, treatment documentation, requirements and characterization of equipment, safety aspects, hyperthermia staff requirements and instrumentation for quality assurance.

Quality assurance for radiofrequency regional hyperthermia

Today most treatments with regional hyperthermia are applied using radiofrequency systems with 'focus' steering by amplitude and phase control. This paper deals with quality assurance procedures developed to ensure controlled and safe treatments in such systems. Our results show how the deviations between requested and observed phase and amplitude vary with frequency, and how these deviations depend on both the geometry of the object (phantom) inside the system and the power level applied. The results also indicate that the investigated systems' internal quality assurance procedures were inadequate and that additional procedures should be applied. Since the system parameters depend on patient and treatment specific conditions it is concluded that there is a need for QA measurements before or during treatment. This paper deals specifically with the commercial BSD-2000 system from BSD Medical Corp. in Salt Lake City, Utah, as installed in Bergen, but the procedure outlined can be applied to other phase and amplitude-controlled RF-RHT systems with only minimal adjustments.

The role of an advanced thermotherapy device in prostatic voiding dysfunction

OBJECTIVES

To investigate the efficacy of an advanced transurethral thermotherapy (TUMT) device (T3, Urologix) using urodynamic analysis in addition to the standard evaluation protocol in patients with symptomatic benign prostatic hyperplasia (BPH).

PATIENTS AND METHODS

Fifty men with symptomatic BPH were assessed using the AUA symptom score, uroflowmetry and ultrasonography (to determine prostatic volume and residual urinary volume) before and 6 weeks, 3, 6 and 12 months after thermotherapy. TUMT was delivered using a focused microwave energy system for 1 h in each patient, treated on an out-patient basis. Video pressure flow studies with advanced urodynamic analysis were also performed before and 3 months after treatment.

RESULTS

The mean AUA symptom score decreased by 63%, the mean peak flow rate increased by 64% and the post-void residual volume decreased by 30% 3 months after treatment; this improvement was maintained at one year after treatment. Advanced urodynamic analysis showed that 52% of the patients had a decreased severity of obstruction. Furthermore, the efficiency of detrusor contraction improved in 86% of the patients. The improvement in the symptom score, flow rate and residual urine was significantly better in patients with marginal obstruction than in patients with unequivocal obstruction.

CONCLUSION

Urodynamic analysis can predict the treatment outcome of TUMT and the results of thermotherapy are significantly better in patients with marginal prostatic bladder outflow obstruction.

Biological rationale and clinical experience with hyperthermia

Hyperthermia (HT) as an adjunct to radiation therapy (RT) has been a focus of interest in cancer management in recent years there have been numerous randomized and nonrandomized studies conducted to assess the efficacy of HT combined with either RT or chemotherapy especially in the treatment of superficially seated malignant tumors. The major impact of HT is currently on locoregional control of tumor. Heat may be directly cytotoxic to tumor cells or inhibit repair of both sublethal and potentially lethal damage after radiation. These effects are augmented by the physiological conditions in tumor that lead to states of acidosis and hypoxia. Blood flow is often impaired in tumor relative to normal tissues, and HT may lead to a further decrease in blood flow and augment heat sensitivity. Three major areas of clinical investigation have borne the greatest fruit for HT as adjunctive therapy to RT. These include recurrent and primary breast lesions, melanoma, and head and neck neoplasms. Thermal enhancement ratio was increased in all cases and is approximately 1.4 for neck nodes, 1.5 for breast, and 2 for malignant melanoma. In general, the most important prognostic factors for complete response (CR) are RT dose, tumor size and minimal thermal parameters minimal thermal dose (t43min), mean minimal temperature (Tmin) or T90, i.e., temperature exceeded by 90% of thermal sensors]. The number of HT fractions administered per week appears to have no bearing on the overall response, which may be indicative of the effects of thermotolerance. The total number of HT fractions delivered also appears irrelevant provided adequate HT is delivered in one or two sessions. The major prognostic factors for the duration of local control were tumor histology, concurrent RT dose, tumor depth and Tmin. Although numerous single institution studies showed increased CR rates and improved local control, the efficacy of HT as an adjunct to RT should be assessed with well-designed multi-institutional randomized clinical trials. Such clinical trials are underway.

Dose uniformity in MECS interstitial hyperthermia: the impact of longitudinal control in model anatomies

The quality of temperature distributions that can be generated with the multi-electrode current source (MECS) interstitial hyperthermia system, which allows 3D control of the spatial SAR distribution, has been investigated. For the investigations, computer models of idealized anatomies were used. These anatomical models did not contain discrete vessels. Binary-media anatomies, containing media interfaces oriented parallel, perpendicular or oblique with respect to the long axis of the implant, represent simple anatomies which can be encountered in the clinic. The implant volume was about 40 cm3. A seven-catheter hexagonal implant geometry with a nearest-neighbor distance of 15 mm was used. In each interstitial probe between one and four electrodes with a diameter of 2.1 mm were placed along an "active section' with a length of 50 mm. The electrode segments had lengths of 50, 20, 12 and 9 mm. This study shows that even with high contrasts in electrical and thermal conductivity in the implant it remains possible to obtain satisfactory temperature distributions with the MECS system. Due to its 3D spatial control the temperature homogeneity in the implant can be made quite satisfactory, with T10-T90 of the order of 2-3 K. Treatment planning must ensure that the placement of the current source electrodes is compatible with the media configuration.

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.

Quality control of the SIGMA applicator using a lamp phantom: a four-centre comparison

An elliptical phantom with a fat-equivalent ring and lamp matrix was developed for observing the power distribution in ring applicators used for regional hyperthermia. This phantom was used on four European BSD-2000-type therapy systems under routine conditions to test the quality of the SIGMA-60 applicator (systems in Berlin, Essen, Munich and Rotterdam). Frequency-dependent focusing imbalances were observed in all systems. At the time of the quality control test two of the systems displayed considerable errors in their settings. The system setups and possible ways of correcting errors are described in detail. Small maladjustments are caused by coupling effects between antennas and their surroundings and by interactions between the coaxial cables which supply the power. Serious distortions can be caused by phase errors and defects in cables or plugs; the latter can result in significant long-term restrictions on the ability to control the SAR (specific absorption rate) distribution in a way the user may not notice. The measurements gained from these four systems confirm the need for a practical and universal procedure for quality control in regional hyperthermia.

Performance evaluation of annular arrays in practice: the measurement of phase and amplitude patterns of radio-frequency deep body applicators

An approach to a solution of two major problems in operating Annular Phased Arrays in deep body hyperthermia is presented: an E-field sensor capable of measuring phase and amplitude at 70 MHz and the concept of a power transmission factor to determine the effective amplitude of each applicator. In the four-waveguide Phased Array operating at 70 MHz, which is in clinical use at the department of Radiotherapy of the Academic Medical Center (AMC), the incident fields of the waveguides were scanned in phase and amplitude over the complete aperture midplane, inside an elliptical and a square phantom filled with saline. As a check on the application of the superposition principle, superpositions of the incident fields were compared with the electric field in the measured interference set-ups. With all four applicators radiating at equal amplitude and in phase, the maximum difference over the complete midplane of the phantom between superimposed and measured interference scans was 20% and 10 degrees in the elliptical phantom, and 20% and 30 degrees in the square phantom. After having determined nominal amplitude and phase patterns by a vector probe, any interference set-up can be superimposed from measurement of the actual incident field of each applicator. Therefore, the availability of a vector sensor as described here will contribute to solve a problem of hyperthermia quality assurance: the performance evaluation of Phased Arrays.

A recommended revision in the RTOG thermometry guidelines for hyperthermia administered by ultrasound

RTOG thermometry guidelines for clinical trials of hyperthermia using planar ultrasound recommended that temperatures be mapped in polyurethane catheters by use of single-junction copper-constantan thermocouples. These guidelines were based on an assumption that the error in temperature measurement due to thermal conduction would generally not exceed +/- 0.3 degrees C. The validity of this assumption was tested with a commercially available single-junction copper-constantan thermocouple. The width of the point spread function, an indicator of the relative magnitude of the conduction error, was five times greater than expected. As a result, the conduction error is projected to exceed 0.3 degrees C in a temperature gradient of only 1.5 degrees C/cm. This projection was confirmed by mapping a thermal peak which simulates a typical clinical temperature profile. This peak had an amplitude of 6 degrees C, a full-width at half-maximum of 3.5 cm, and a maximum gradient of approximately 3 degrees C/cm. Temperatures measured at 0.5-cm intervals over the span of this peak were in error by a mean of +/- 0.6 degrees C. It is strongly recommended that the RTOG guidelines be revised to replace copper-constantan thermocouples with manganin-constantan single- or multi-junction thermocouples which will assure that the conduction error will be < +/- 0.3 degrees C.

The use of generalized cell-survival data in a physiologically based objective function for hyperthermia treatment planning: a sensitivity study with a simple tissue model implanted with an array of ferromagnetic thermoseeds

PURPOSE

A physiologically based objective function for identifying a combination of ferromagnetic seed temperatures and locations that maximizes the fraction of tumor cells killed in pretreatment planning of local hyperthermia.

METHODS AND MATERIALS

An objective-function is developed and coupled to finite element software that solves the bioheat transfer equation. The sensitivity of the objective function is studied in the optimization of a ferromagnetic hyperthermia treatment. The objective function has several salient features including (a) a physiological basis that considers increasing the fraction of cells killed with increasing temperatures above a minimum therapeutic temperature (Tmin,thera), (b) a term to penalize for heating of normal tissues above Tmin,thera, and (c) a scalar weighting factor (gamma) that has treatment implications. Reasonable estimates for gamma are provided and their influence on the objective function is demonstrated. The cell-kill algorithm formulated in the objective function is based empirically upon the behavior of published hyperthermic cell-survival data. The objective function is shown to be independent of normal tissue size and shape when subjected to a known outer-surface, thermal boundary condition. Therefore, fractions of cells killed in tumors of different shapes and sizes can be compared to determine the relative performance of thermoseed arrays to heat different tumors.

RESULTS

In simulations with an idealized tissue model perfused by blood at various rates, maxima of the objective function are unique and identify seed spacings and Curie-point temperatures that maximize the fraction of tumor cells killed. In ferromagnetic hyperthermia treatment planning, seed spacing can be based on maximizing the minimum tumor temperature and minimizing the maximum normal tissue temperature. It is shown that this treatment plan is less effective than a plan based on seed spacings that maximize the objective function.

CONCLUSIONS

It is shown that under the assumptions of the model and based on a desired therapeutic goal, the objective function identifies a combination of thermoseed temperatures and locations that maximizes the fraction of tumor cells killed.

Quality assurance in various radiative hyperthermia systems applying a phantom with LED matrix

The Amsterdam phantom with LED-matrix is applied as an instrument in testing the performance of four types of radiative deep-body hyperthermia systems, which are in clinical use in Germany and The Netherlands. The devices tested were Essen's BSD-1000, Berlin's BSD-2000, Utrecht's Coaxial TEM applicator and Amsterdam's Four-waveguide-array. Photographs were taken of the matrix of dipoles loaded with light-emitting diodes (LED) to visualize the distribution of the RF power deposition or specific absorption rate (SAR) in the aperture midplane. The utility of the phantom with LED matrix for various types of radiative hyperthermia systems is demonstrated. Within this preliminary study, the influence of important parameters on the SAR-pattern in the aperture midplane was demonstrated. After corrections on the phase relation of the applicators a central focus in the SAR distribution could be realized in all systems and could also be moved in any direction. The patterns of the central focus changed in its absolute values and its proportions depending on the relative relations of phase and amplitude of the lateral applicators with respect to the top and bottom applicator. Frequency dependency was recognized for the central focus of the BSD-1000 as well as for the irradiation pattern of a single applicator for the BSD-2000. In the Coaxial TEM applicator it was demonstrated that the dimension of the open water bolus influenced the absolute value of SAR in the aperture midplane.

Development and testing of SAR-visualizing phantoms for quality control in RF hyperthermia

A new prototype of an elliptical standard phantom with fat-equivalent walls and a lamp matrix for SAR (specific absorption rate) visualization has been developed. This paper outlines the manufacture of solid components based upon either polyester resin or epoxy resin, as well as the adjustment of their electrical conditions (epsilon r, sigma) by admixtures of carbon and/or aluminium powder. Visualizing sensors (LED = light-emitting diodes, miniature lamps) are evaluated with respect to their transformation of electric field strength into light. Standard SAR patterns of the hyperthermia system BSD-2000 have been semiquantitatively assessed by the visualizing technique (power stepping method) and quantitatively by E field sensor scans. Extracted iso-SAR distributions are in good agreement with E field sensor scans performed with a lamp sensor coupled to a fibre or using a dipole probe with high resistive leads. The requirement for periodic quality control of SAR patterns of RF (radio frequency) hyperthermia systems is demonstrated. Comparisons between techniques are given, specifically with respect to the LED phantom of Schneider and van Dijk.

[New microwave transurethral hyperthermia for benign prostatic hyperplasia--clinical evaluation]

Several types of hyperthermic apparatuses are employed to treat benign prostatic hyperplasia (BPH). As the prostate surrounds the urethra, we believed that transurethral heating allowed for more efficient and uniform heating. A new effective apparatus for this objective was developed. The size of our hyperthermic apparatus was about 52 x 45 x 20 centimeters and the originating frequency was 2,450 +/- 30 MHz. We used T-type thermocouples as temperature sensors. The transurethral applicator had a cooling system. Thirty patients complaining of obstructive symptoms due to BPH were treated. Hyperthermia was performed 3-6 times for each patients (two times per week). Each procedure was performed for 60 minutes. The temperature was controlled at 39 degrees C on the urethral surface (43 degrees C at prostate). The overall efficacy of this treatment was effective in 23 of the 30 patients (76.7%). In addition, there were no severe complications. As the size of this apparatus was miniaturized, it could be used at the bed side.