Calculation of mean central dose in interstitial brachytherapy using Delaunay triangulation.

In 1997 the ICRU published Report 58 "Dose and Volume Specification for Reporting Interstitial Therapy" with the objective of addressing the problem of absorbed dose specification for reporting contemporary interstitial therapy. One of the concepts proposed in that report is "mean central dose." The fundamental goal of the mean central dose (MCD) calculation is to obtain a single, readily reportable and intercomparable value which is representative of dose in regions of the implant "where the dose gradient approximates a plateau." Delaunay triangulation (DT) is a method used in computational geometry to partition the space enclosed by the convex hull of a set of distinct points P into a set of nonoverlapping cells. In the three-dimensional case, each point of P becomes a vertex of a tetrahedron and the result of the DT is a set of tetrahedra. All treatment planning for interstitial brachytherapy inherently requires that the location of the radioactive sources, or dwell positions in the case of HDR, be known or digitized. These source locations may be regarded as a set of points representing the implanted volume. Delaunay triangulation of the source locations creates a set of tetrahedra without manual intervention. The geometric centers of these tetrahedra define a new set of points which lie "in between" the radioactive sources and which are distributed uniformly over the volume of the implant. The arithmetic mean of the dose at these centers is a three dimensional analog of the two-dimensional triangulation and inspection methods proposed for calculating MCD in ICRU 58. We demonstrate that DT can be successfully incorporated into a computerized treatment planning system and used to calculate the MCD.

The detection of changes in mammographic densities.

We previously reported reductions in mammographic densities in women participating in a trial of a gonadotropin-releasing hormone agonist (GnRHA)-based regimen for breast cancer prevention. In our previous report, we compared (by simultaneous evaluation) three basic elements of mammographic densities. The purpose of the present study was to evaluate whether a standard (expert) method of measuring mammographic densities would detect such changes in densities and whether a novel nonexpert computer-based threshold method could do so. Mammograms were obtained from 19 women at baseline and 12 months after randomization to the GnRHA-based regimen. The extent of mammographic densities was determined by: (a) a standard expert outlining method developed by Wolfe and his colleagues (Am. J. Roentgenol., 148: 1087-1092, 1987); and (b) a new computer-based threshold method of determining densities. The results from both the expert outlining method and the computer-based threshold method were highly consistent with the results of our original (simultaneous evaluation) method. All three methods yielded statistically significant reductions in densities from baseline to the 12-month follow-up mammogram in women on the contraceptive regimen. The difference between the treated and the control group was statistically significant with the expert outlining method and was of borderline statistical significance with the computer-based threshold method. The computer-based results correlated highly (r > 0.85) with the results from the expert outlining method. Both the standard expert outlining method and the computer-based threshold method detected the reductions we had previously noted in mammographic densities induced by the GnRHA-based regimen.

Conformal episcleral plaque therapy.

PURPOSE: Episcleral plaque therapy (EPT) with sealed 125I sources is widely used in the treatment of choroidal melanoma. In EPT, as elsewhere in radiotherapy, concern for normal tissue tolerance has frequently been a dose-limiting factor. The concept of conformal therapy, which seeks to improve dose homogeneity within the tumor and greatly reduce the dose to uninvolved structures may provide a solution to this problem. Radioactive sources are typically distributed uniformly over the surface of an episcleral plaque and are sometimes offset slightly from the scleral surface to reduce the dose to the sclera relative to the apex and prescribed therapeutic margin at the tumor base. Nevertheless, it is not uncommon for scleral dose to exceed the dose to the apex of intermediate to tall tumors by a factor of 4 or more. The availability of low-energy sealed sources such as 125I prompted the development of gold-backed plaques to shield noninvolved periocular tissues. The concept of shielding can be extended to include collimation of individual sources. The potential advantages of individual source collimation include reduced scleral dose, more homogeneous tumor dose, and superior shielding of adjacent normal structures such as the fovea as compared to previous plaque designs. METHODS AND MATERIALS: A three-dimensional treatment-planning system has been extended to design a plaque that incorporates individually collimated 125I sources. Thermoluminescent dosimetry (TLD) and radiochromic film were used to compare calculated dose-rate distributions with measured dose rates in an acrylic phantom. RESULTS: Calculations predict that source collimation in the form of a "slotted" gold plaque will achieve the purposes of the study. The collimating effect of the slots is demonstrated qualitatively using radiochromic film, and the accuracy of the calculation is demonstrated quantitatively with TLD. CONCLUSION: The episcleral plaque described in this report is simpler to assemble than previous plaque designs. It produces a more homogeneous dose distribution in the tumor, reduces scleral dose by up to 50% as compared to conventional designs, and significantly reduces radiation dose to uninvolved structures adjacent to the plaque.

Transurethral hyperthermia for benign prostatic hyperplasia: long term results.

Transurethral resection of the prostate (TURP) is the only recognized treatment in patients with benign prostatic hyperplasia (BPH). Transurethral hyperthermia (TUHT) was used as an alternative treatment in patient who refused TURP. From 1987 to 1988, 21 BPH patients with moderate to severe symptoms and signs of prostatism were treated with TUHT in a phase I trial. Mean pre-treatment subjective and objective values were: total symptom score (TSS) 13.5, obstructive symptom score (OSS) 6.5, irritative symptom score (TSS) 7.0, peak flow rate (PFR) 11.6 cc/sec, post-voiding residual volume (PRV) 187 cc, and prostate volume (PV) 93 cc. TUHT was given for a total of 177 sessions (mean 8.4), each of 60 min duration at a steady state. Temperature was recorded continuously on the urethral surface, in all treatments. It ranged from Tmin 40.3 degrees C to Tmax = 49.2 degrees C and Tmean = 44.1 degrees C. The mean minimum temperature of > or = 42 degrees C was obtained in 98% of the TUHT sessions. Treatments were given on an outpatient basis without sedation or anaesthesia. Treatment tolerance was excellent with minor acute toxicity common (71% of patients), of no clinical importance and with no late complications. Of the 21 patients treated, 17 (81%) had an objective and 15 (71%) a subjective improvement recorded at 6 months post-treatment. This statistically highly significant improvement included: 61% decrease in TSS; 66% decrease in OSS; 55% decrease in ISS; 42% increase in PFR; 55% decrease in PRV; and 21% decrease in PV. Of the 17 patients with objective improvement, nine have maintained their response to TUHT for a minimum period of over six years, two relapsed at 11 and 40 months, respectively, and six patients died of cardiovascular causes maintaining their response to death. This study has demonstrated TUHT treatment efficacy with no major or clinically important toxicity in BPH patients. A relative weakness of this report is a lack of verification of objective study parameters in the patients at seven years post-treatment. Prospective randomized trials are needed to define the role of TUHT in the management of BPH patients.

Episcleral plaque thermoradiotherapy of posterior uveal melanomas.

Episcleral plaque radiotherapy is a widely applied treatment for selected patients with uveal melanomas. This treatment is well tolerated but may produce severe late radiation complications resulting in decreased visual acuity that reduces the attractiveness of conservative therapy. The purpose of this study was to access if the addition of episcleral hyperthermia decreases late radiation complications through radiation dose reduction while maintaining high incidence of local tumor control. In a 3-year period, episcleral plaque thermoradiotherapy was given to 25 patients with uveal melanoma in a Phase I study. The mean tumor height was 6.2 mm and the mean tumor basal area was 173 mm(2). The mean radiation dose given to the tumor apex was 72.2 Gy and the mean hyperthermia temperature, given once for 45 min, was 43.5 degrees C. Of the 25 patients treated, 22 (88%) showed tumor height reduction, 2 (8%) showed no change, and 1 (4%) had an increase in tumor height. At the last follow-up (range, 20-68 months; mean, 31.2 months), a 43% mean tumor height reduction was recorded (p = 0.0002). Of the 22 patients initially showing tumor regression, 2 (9%) had subsequent tumor progression. At least ambulatory vision (>5/200) was maintained by 20 (80%) patients. Severe complications, including hemorrhagic retinal detachment and a large vitreous hemorrhage, were seen in 2 (8%) patients early in this Phase I study. The treatment program was well tolerated by the study patients. Severe late treatment toxicity was sharply reduced by limiting the mean scleral temperature to < or equal to 44 degrees C. This study employing 30% lower radiation doses, showed tumor regression in the majority of patients. Longer follow-up is needed to assess long-term treatment efficacy and late treatment complications.

Tumor localization using fundus view photography for episcleral plaque therapy.

The accurate localization of ophthalmic tumors on the scleral surface is important when calculating radiation dose to the tumor and adjacent structures from episcleral I-125 plaques. This is particularly true for tumors close to the fovea or optic nerve. A fundus view diagram of the eye is often used by ophthalmologists to describe the size and shape of the tumor perimeter as well as its geographical location on the retinal surface. There is, however, an inherent inaccuracy associated with the use of a hand drawn diagram to obtain physical measurements. A computer planning program has been developed which uses CT and a digitized photographic montage of the posterior hemisphere to estimate the size and location of posteriorly located tumors. A simple phantom was constructed to test the software and a direct comparison made between planned versus measured tumor size and location in an excised eye.

Transurethral microwave hyperthermia for benign prostatic hyperplasia: the Leuven clinical experience.

Local microwave hyperthermia, delivered transurethrally or transrectally, is a new treatment modality for benign prostatic hyperplasia. We started transurethral application, delivering 915-MHz microwaves at the prostatic urethra using a helical microwave antenna incorporated in a Foley catheter. This hyperthermia was given without a urethral surface cooling system. Thermophysical testing of the applicator proved therapeutic efficacy in vitro and in vivo. Pathologic studies demonstrated hyperthermia-induced lesions in the periurethral prostatic tissues and permitted us to hypothesize a working mechanism of transurethral hyperthermia. Clinical Phase I and II studies showed clinical efficacy in patients with urinary retention or prostatism secondary to benign hyperplasia, especially in bilobar or trilobar prostatic configurations. While awaiting results of further pathologic and thermophysical experimental work and ongoing Phase II and III studies, we consider transurethral hyperthermia an investigational but promising conservative treatment modality for benign prostatic hyperplasia.

Utilization of a multilayer polyacrylamide phantom for evaluation of hyperthermia applicators.

A muscle-stimulating material made of polyacrylamide gel (PAG) for testing various kinds of hyperthermia applicators was investigated. The permittivity and conductivity dispersion of PAG, as well as an internal wavelength and penetration depth, were in good agreement with those of actual muscle at frequencies between 500 MHz and 3 GHz. A single formula for PAG covering three ISM bands, most commonly used for hyperthermia, 433, 915 and 2450 MHz, is presented. The physical properties of the PAG phantom allow any desired form or shape to be moulded, including shapes conforming to the actual geometry of an interstitial or intracavitary applicator. Utilization of a multilayer phantom makes possible the generation of experimental three-dimensional specific absorption rate (SAR) distributions composed from several two-dimensional SAR images at different depths or radial distances from the applicator. Spatial resolution of 1 mm can be achieved. The two-dimensional SAR distributions at different depth values for commercial superficial applicator, an interstitial antenna and a new oesophageal applicator are presented.

Temperature steering in prostate by simultaneous transurethral and transrectal hyperthermia.

Localized hyperthermia (HT) is presently under investigation as a treatment for benign prostatic hyperplasia and carcinoma of the prostate (CaP). One popular approach employs a transrectal (TR) device, a directional microwave (MW) applicator inserted into the rectum and aimed at the prostate. Alternatively, in the transurethral (TU) technique, a symmetrically radiating MW antenna is placed directly within the prostatic urethra. Used individually, TR applicators are capable of effectively heating (> 42 degrees C) the prostate up to 2 cm from the rectum, whereas TU applicators selectively heat the periurethral tissue with effective radial penetration of about 0.6 cm. Neither technique is of much value in heating the anterior prostate. In general, the highest temperatures are produced in the tissue immediately adjacent to the surface of intracavitary microwave devices. However, when MW antennas are used in arrays, the resulting heating pattern can differ significantly from that of the individual antennas. Heating at depth can be selectively enhanced and "steered" by adjusting the phase relationship between the devices. Prostatic temperature profiles were measured in 6 patients treated with TR alone, TU alone, and simultaneous TR and TU heating. In the combined treatments different phase relationships between the antennas were applied. We found that a higher temperature could be produced in the center of the prostate than on the surface of either applicator for certain phase relationships, and that the temperature profiles could be changed by shifting phase. The results of these measurements are in agreement with those of a computer simulation. Based on the above data we feel the combined use of TU and TR hyperthermia may be justified in Phase I-II trials for patients with locally advanced CaP.

Transurethral hyperthermia for benign prostatic hyperplasia patients with retention.

From 1989 to 1990, 32 poor surgical risk patients with urinary retention were treated with transurethral microwave hyperthermia at the department of urology, University of Leuven in Belgium. Mean patient age was 73 years (range 58 to 90 years) and mean duration of retention was 4 weeks (range 3 to 12 weeks). Followup ranged from 13 to 82 weeks, with a mean of 31 weeks. Bilobar or trilobar hyperplasia was diagnosed in 25 patients (78%), while 7 (22%) had median lobe or median bar hypertrophy. The mean prostatic volume was 52 cc (range 25 to 150 cc). Transurethral microwave hyperthermia was given with a helical antenna at 915 MHz. once or twice per week. The mean number of transurethral microwave hyperthermia sessions was 8.9 (range 5 to 10). Each session consisted of a 60-minute treatment at a mean maximum temperature of 45.4C (range 43.7 to 47.2C), average temperature 43.9C (range 42.7 to 45.5C) and minimum temperature 42.0C (range 40.2 to 43.0C). The temperature was continuously monitored, including thermal mapping in all patients. Of the 25 patients who presented with bilobar or trilobar hyperplasia 18 (72%) were catheter-free for the duration of followup. Of the 7 median lobe or median bar patients 1 (14%) showed sufficient improvement to warrant catheter removal. This patient, however, had recurrent retention 4 months after transurethral microwave hyperthermia. In patients with bilobar and trilobar hyperplasia a strong correlation was observed among maximum temperature (p = 0.0006), average temperature (p = 0.0033) and treatment response. As expected, no such correlation existed between minimum temperature and response to treatment (p = 0.56). Our study has again demonstrated therapeutic activity in patients with benign prostatic hyperplasia treated with transurethral microwave hyperthermia. A new finding was a strong correlation between temperature and response.

Episcleral plaque radiotherapy in the treatment of uveal melanomas.

During an 8-year period, 85 patients with uveal melanomas were treated with episcleral plaque radiotherapy (EPRT). The T-stage was: T1-3 (4%), T2-29 (34%) and T3-53 (62%). The mean tumor elevation was 6.1 mm. Radiation dose was prescribed at the tumor apex and at D5mm. The mean D5mm dose was 150.1 Gy (range 70.5-430 Gy) and the mean dose at the apex was 102.6 Gy (range 29.8-200 Gy). Useful vision (greater than 5/200) was maintained in 73% of patients. The 5-year actuarial survival was 88%. Metastatic disease developed in 9 (11%) patients, 6 of whom died of their disease. Basal tumor dimensions were important factors predicting metastatic disease, p = 0.002. A decrease in tumor evaluation was seen in 82%. There was a much lower incidence of decrease in tumor radial and circumferential dimensions, 47.5 and 46%, respectively, p less than 0.001. Treatment complications were common (56%), particularly in patients with large tumors (72%), p = 0.04. The incidence of complications was higher in patients treated prior to 1988 as compared to those who were treated more recently (67 vs 35%, p = 0.010). There were 13 (15%) patients who had enucleation. This included 12 treated before 1986 and 1 patient treated subsequently (46 vs 2%, p less than 0.001). In a univariate analysis, tumor height and radiation dose at D5mm were important factors predicting enucleation, p = 0.004. In a multivariate analysis, however, the most important factor predicting enucleation was treatment administration prior to 1986, p less than 0.001). A sharp decrease in the incidence of severe complications, including enucleation, as seen after 1985, is likely due to a major effort in treatment optimization.

Episcleral plaque thermoradiotherapy in patients with choroidal melanoma.

From 1988 to 1991, 21 patients with uveal melanoma were treated in a Phase I study with episcleral plaque radiotherapy (EPRT). This irradiation was combined with localized current field episcleral hyperthermia (LCFHT). Tumor stage was: T3 = 15 (71%) and T2 = 6 (29%). Follow-up ranged from 2 to 42 months (mean 9.2 months). EPRT was given using custom built I-125 gold plaques. Radiation doses to the tumor apex ranged from 13 to 123 Gy (mean dose 70.0 Gy) given at a mean dose rate of 55 cGy/hr. LCFHT was given with 500 KHz frequency for 45 min immediately before EPRT. The temperature was controlled on the scleral surface using four thermocouples. T mean ranged from 42.5 degrees C to 45 degrees C +/- 0.5 degrees C (mean 43.4 degrees C). The study patients showed rapid tumor necrosis. A 25% mean decrease of apical tumor dimension was noted, p = 0.0007. At least ambulatory vision (greater than 5/200) was maintained by 17/21 (81%) patients. Visual acuity was seen to improve greater than 6 months post-plaque therapy in 10 (48%) study patients. This was following an intermediate decrease in visual acuity. Severe complications, including large hemorrhagic retinal detachment and large vitreous hemorrhage, were seen in two (9.5%) of the early study patients. A mean scleral temperature reduction to less than or equal to 44 degrees C +/- 0.5 degrees C resulted in good treatment tolerance and a lack of serious complications in subsequently treated patients. A Phase II prospective randomized trial comparing LCFHT with 60 versus 80 Gy EPRT dose to the tumor apex is currently being activated for patients with choroidal melanoma.

Regional hyperthermia in patients with recurrent genitourinary cancer.

During a 6-year period, 53 patients with advanced tumors of the genitourinary tract were treated in Phase I protocols with deep regional hyperthermia in combination with irradiation (83%) or in combination with chemotherapy (11%). Primary tumors included those of bladder in 22 patients (41%), prostate in 20 patients (37%), kidney in 9 patients (17%), and ureter testicle or adrenal in 3 patients (5%). The majority (77%) had prior definitive therapy and had experienced treatment failure, and 11% had clinically important distant metastases. Treatment consisted of deep regional hyperthermia (mean of 4 sessions). In addition, 44 patients (83%) received irradiation (mean dose 39.2 Gy). The 1- and 3-year actuarial survival was 60% and 56%, respectively. Patients with carcinoma of the prostate had a 1- and 3-year survival of 82%. Complete response was observed in 7 patients (13%), partial response in 8 (15%), and nominal response in 13 (25%). Complete and partial response correlated well with histology of the tumor (adenocarcinoma), radiation dose (greater than 50 Gy), primary site (prostate, kidney), and treatment (hyperthermia-radiotherapy combination), (p = 0.02). There was no such correlation between response and thermal dose (p = 0.13). The treatment tolerance was good in 79% of patients. Treatment toxicity was limited to acute side effects, including pain during hyperthermia (47%), tachycardia greater than 140/min (7%), and blister formation in the treated area (4%). Phase II studies in previously untreated patients with locally advanced tumors of bladder, prostate, and kidney are needed for evaluation of the role of deep regional hyperthermia in the management of these cancers.

Combined localized current field hyperthermia and irradiation for intraocular tumors.

Ten patients with large melanomas and one patient with recurrent retinoblastoma were treated with combined localized current field (LCF) hyperthermia and iodine 125 irradiation delivered by episcleral plaque. Tumors were heated to 43 degrees to 45 degrees C for 28 to 45 minutes. Localized current field hyperthermia when combined with irradiation appeared to induce rapid tumor necrosis. One eye enucleated 17 hours after treatment showed only focal necrosis of the melanoma, while another eye demonstrated extensive necrosis 60 hours after treatment. In all remaining eyes, tumor regression occurred within the first month of treatment. Complications included cataract formation in six eyes, hemorrhagic retinal detachment in five eyes, and phthisis in two eyes. Complications from combined therapy of large intraocular tumors in this series appeared to result from the rapid necrosis of the tumor and secondary intraocular inflammation. Intraocular temperature dosimetry measurements demonstrated a temperature gradient of not more than -0.23 degrees C/mm-1 per axial millimeter from the episcleral plaque surface to the apex of the tumor. The authors believe that LCF hyperthermia could be a suitable means of application of hyperthermia in patients with intraocular tumors if further modifications were performed to reduce ocular complications.

Algorithm for dosimetry of multiarc linear-accelerator stereotactic radiosurgery.

Treatment planning for multiarc radiosurgery is an inherently complex three-dimensional dosimetry problem. Characteristics of small-field x-ray beams suggest that major simplification of the dose computation algorithm is possible without significant loss of accuracy compared to calculations based on large-field algorithms. The simplification makes it practical to efficiently implement accurate multiplanar dosimetry calculations on a desktop computer. An algorithm is described that is based on data from fixed-beam tissue-maximum-ratio (TMR) and profile measurements at isocenter. The profile for each fixed beam is scaled geometrically according to distance from the x-ray source. Beam broadening due to scatter is taken into account by a simple formula that interpolates the full width at half maximum (FWHM) between profiles at isocenter at different depths in phantom. TMR and profile data for two representative small-field collimators (10- and 25-mm projected diameter) were obtained by TLD and film measurements in a phantom. The accuracy of the calculational method and the associated computer program were verified by TLD and film measurements of noncoplanar multiarc irradiations from these collimators on a 4-MV linear accelerator. Comparison of film measurements in two orthogonal planes showed close agreement with calculations in the shape of the dose distribution. Maximal separation of measured and calculated 90%, 80%, and 50% isodose curves was less than or equal to 0.5 mm for all planes and collimators. All TLD and film measurements of dose to isocenter agreed with calculations to within 2%.

A comparison of transurethral and transrectal microwave hyperthermia in poor surgical risk benign prostatic hyperplasia patients.

From 1987 to 1989, 36 poor surgical risk patients with benign prostatic hyperplasia (BPH) were treated with transrectal or transurethral microwave hyperthermia. Most of the 36 patients treated (85%) had severe signs and symptoms of urinary outflow obstruction. Of the patients 22 (61%) underwent transrectal and 14 (39%) underwent transurethral hyperthermia. Followup ranged from 10 to 28 months (mean 19 months) for the transrectal hyperthermia group and 7 to 16 months (mean 10 months) for the transurethral hyperthermia group. The patients were given 6 hyperthermia sessions of 30 minutes each with the temperature controlled on the rectal or urethral surface at 45C. Hyperthermia was well tolerated with mild acute toxicity and no late complications were observed. In the important subjective and objective parameters, major improvement was noted more frequently in the 14 transurethral than in the 22 transrectal hyperthermia treated patients (p less than 0.05). The Food and Drug Administration severity score, prostate volume, post-voiding residual volume and urethral flow showed substantial improvement in 79, 86, 79 and 79%, respectively, of the 14 transurethral hyperthermia treated patients compared to 41, 45, 82 and 82%, respectively, for the 22 transrectal hyperthermia treated patients. A prospective randomized trial comparing transrectal and transurethral hyperthermia is required to define the role of each treatment mode in patients with BPH.

Management of carcinoma of the esophagus: the role of radiotherapy.

This is an analysis of treatment results over a 23-year period in 241 patients with carcinoma of the esophagus. The treatment for unresectable patients was external beam radiotherapy (EBRT) alone (mean dose 55 Gy) in 137 (57%) combined with brachytherapy (mean dose 50 + 40 Gy) in 46 (19%), and chemotherapy alone in 3 (1%) patients. In the 55 resectable patients, treatment was resection alone in 9 (4%), and combined with radiotherapy (mean dose 43 Gy) in 46 (19%) patients. The 1-, 2-, and 5-year survival for the 241 patients was 36, 15, and 5%, respectively (median 38 weeks). The 5-year survival was 18% for radiotherapy (RT)-surgery (S) patients, 11% for EBRT with brachytherapy, 2% for EBRT alone, and 0% for patients who had S alone, p less than 0.001. Survival correlated well with initial performance status, treatment, stage of disease, tumor size, radiation dose, and degree of response, p less than 0.001, but not with tumor location in the esophagus and patients' race and sex, p = 0.44. Serious complications occurred in 5 (2%) patients treated with RT alone and in 4 (7%) patients treated with S alone or combined with RT. The leading cause of death was persistent or recurrent tumor in the chest found in 39% patients.

Interstitial temperature measurements during transurethral microwave hyperthermia.

Microwave hyperthermia is presently being investigated as a treatment for alleviating the symptoms of urinary outlet obstruction associated with benign prostatic hyperplasia. Two clinical techniques using intracavitary microwave applicators are being evaluated for safety and efficacy at various institutions. The transrectal technique uses a directional microwave radiator that is inserted into the rectum adjacent to the prostate. The transurethral approach uses a symmetrically radiating applicator located within the prostatic urethra. Transrectal prostatic heating techniques require surface cooling to prevent hazardous temperatures in the intervening rectal mucosa. Since transurethral applicators radiate from within the prostatic urethra, heating is confined to the obstructive tissue immediately surrounding the applicator. Concern has been expressed regarding the possibility of thermal injury to the prostate and adjacent rectum during transurethral hyperthermia treatment. In this report we present interstitial temperature measurements of prostatic and rectal temperatures in 5 patients. Temperature was observed to decrease at a rate of about 6C/cm. outward from the applicator. No clinically significant temperature increase was observed beyond 1 cm, outside the prostatic capsule or in the rectal mucosa.

Transurethral microwave hyperthermia: an alternative treatment for prostadynia?

A total of 15 patients with severe symptoms of prostadynia who were refractory to therapy were treated with transurethral microwave hyperthermia (TUHT) in a phase I trial. All patients had pain as the predominant symptom, 9 (60%) patients gave a history of psychological problems while frequency, urgency, dysuria, nocturia, and impotence were less common symptoms. Treatment consisted of TUHT at 915 MHz given weekly for 5 weeks with a total of 68 treatment sessions and a mean of 4.5 treatments per patient. Each treatment lasted for 60 minutes. The aim was to increase the temperature measured on the urethral surface to greater than or equal to 44 degrees C. T mean for all sessions was 45.5 degrees C. In 91% of treatments, the temperature was greater than or equal to 44 degrees C. Treatment was well tolerated in 87% patients and acute toxicity was mild. Of the 15 patients treated, 2 (13%) did not complete the treatment course due to discomfort during TUHT. Good treatment response, manifested by complete pain relief and a decrease in dysuria, was noted in 7 (47%) patients. A higher (greater than or equal to 46 degrees C) treatment temperature correlated well with good response, P less than .01. Similarly, relief of pain correlated well with the absence of a history of psychological problems, P less than .01. A decrease of obstructive micturition problems was noted in 5 of the 7 patients who had this upon presentation. This study showed evidence of therapeutic activity with the use of TUHT in patients with prostadynia refractory to therapy. The response obtained was limited to less than one-half of the patients. Complete pain relief was obtained in 4 (27%) patients. It is of interest to note that patients who had major benefit did not show evidence of psychological problems and were able to tolerate higher treatment temperatures. The latter could suggest a temperature-related response.

Heating characteristics of a helical microwave applicator for transurethral hyperthermia of benign prostatic hyperplasia.

A new applicator for intraurethral hyperthermic treatment of benign prostatic hyperplasia is described. The applicator uses an insulated helical antenna wound on the outer surface of a silicone urological (Foley) balloon catheter. The balloon catheter assures rapid and reproducible localization of the antenna in the prostatic urethra. Two small cannulae are fixed to the exterior surface of the applicator. One holds a temperature control sensor at a fixed location, the other is used to map temperature along the applicator. Two-dimensional SAR and steady-state temperature distributions measured in a plane tangent to the applicator in a tissue-equivalent phantom are presented, as well as longitudinal temperature distributions measured in situ at the applicator-urethral interface. Prostatic temperatures were also measured intraoperatively. The applicator appears to be capable of elevating temperature to greater than 42 degrees C in a cylindrically symmetric volume of about 4 cm length and about 0.5 cm radial penetration surrounding the antenna. The heating characteristics of this applicator are similar to an earlier design that employed an array of three dipoles. The helical applicator is narrower, more flexible and simpler to use than the earlier design.