In vivo temperature mapping of prostate during treatment with TherMatrx TMx-2000 device: heat field and MRI determinations of necrotic lesions

Issues Critical to the Successful Application of Cryosurgical Ablation of the Prostate

The techniques of present-day cryosurgery performed with multiprobe freezing apparatus and advanced imaging techniques yield predictable and encouraging results in the treatment of prostatic and renal cancers. Nevertheless, and not unique to cryosurgical treatment, the rates of persistent disease demonstrate the need for improvement in technique and emphasize the need for proper management of the therapeutic margin. The causes of persistent disease often relate to a range of factors including selection of patients, understanding of the extent of the tumor, limitations of the imaging techniques, and failure to freeze the tumor periphery in an efficacious manner. Of these diverse factors, the one most readily managed, but subject to therapeutic error, is the technique of freezing the tumor and appropriate margin to a lethal temperature [Baust, J. G., Gage, A. A. The Molecular Basis of Cryosurgery. BJU Int 95, 1187–1191 (2005)]. This article describes the recent experiments that examine the molecular basis of cryosurgery, clarifies the actions of the components of the freeze-thaw cycle, and defines the resultant effect on the cryogenic lesion from a clinical perspective. Further, this review addresses the important issue of management of the margin of the tumor through adjunctive therapy. Accordingly, a goal of this review is to identify the technical and future adjunctive therapeutic practices that should improve the efficacy of cryoablative techniques for the treatment of malignant lesions.

Rezūm System Water Vapor Treatment for Lower Urinary Tract Symptoms/Benign Prostatic Hyperplasia: Validation of Convective Thermal Energy Transfer and Characterization With Magnetic Resonance Imaging and 3-Dimensional Renderings

OBJECTIVE

To evaluate by magnetic resonance imaging the physical effects of convective thermal energy transfer with water vapor as a means of treating lower urinary tract symptoms due to benign prostatic hyperplasia.

METHODS

Sixty-five men with lower urinary tract symptoms were treated with the Rezūm System by transurethral intraprostatic injection of water vapor. A group of 45 of these men consented to undergo a series of gadolinium-enhanced magnetic resonance imagings of the prostate after treatment to monitor the size and location of ablative lesions, their time course of resolution, and the corresponding change in prostate tissue volume. Visualization was conducted at 1 week, 1, 3, and 6 months after treatment.

RESULTS

Outcomes were available for 44 patients. Convective thermal lesions were limited to the transition zone and correlated with targeted treatment locations. At 1 week after treatment, the mean volume of ablative lesions was 8.2 cm(3) (0.5-24.0 cm(3)). At 6 months, whole prostate volume was reduced by a mean of 28.9% and transition zone volume by 38.0% as compared with baseline 1-week images. At 3 and 6 months after treatment, the lesion volumes had reduced by 91.5% and 95.1%, respectively. Lesions remained within the targeted treatment zone without compromising integrity of the bladder, rectum, or striated urinary sphincter.

CONCLUSION

This imaging study confirms the delivery of convective water vapor technology to create thermal lesions in the prostate tissue. Lesions generated underwent near complete resolution by 3 and 6 months after treatment with a concomitant one-third reduction in overall prostate and transition zone volumes.

Accurate field mapping in the presence of B0 inhomogeneities, applied to MR thermometry

PURPOSE

To describe how B0 inhomogeneities can cause errors in proton resonance frequency (PRF) shift thermometry, and to correct for these errors.

METHODS

With PRF thermometry, measured phase shifts are converted into temperature measurements through the use of a scaling factor proportional to the echo time, TE. However, B0 inhomogeneities can deform, spread, and translate MR echoes, potentially making the "true" echo time vary spatially within the imaged object and take on values that differ from the prescribed TE value. Acquisition and reconstruction methods able to avoid or correct for such errors are presented.

RESULTS

Tests were performed in a gel phantom during sonication, and temperature measurements were made with proper shimming as well as with intentionally introduced B0 inhomogeneities. Errors caused by B0 inhomogeneities were observed, described, and corrected by the proposed methods. No statistical difference was found between the corrected results and the reference results obtained with proper shimming, while errors by more than 10% in temperature elevation were corrected for. The approach was also applied to an abdominal in vivo dataset.

CONCLUSION

Field variations induce errors in measured field values, which can be detected and corrected. The approach was validated for a PRF thermometry application.

Temperature mapping near the surface of ultrasound transducers using susceptibility- compensated magnetic resonance imaging

Magnetic resonance imaging (MRI)-based temperature mapping very close to the surface of an ultrasound transducer is not possible due to the large magnetic susceptibility- induced image artifacts that arise from the materials used in transducer construction. Here, it is shown in phantoms that "susceptibility-compensated" MRI sequences can be used to measure thermal increases approximately 1 mm from the surface of a 4-element cymbal array transducer, which has been used widely for noninvasive transdermal drug delivery. The estimated temperatures agree well with those measured using thermocouples.

Transurethral ultrasound applicators with dynamic multi-sector control for prostate thermal therapy: in vivo evaluation under MR guidance

The purpose of this study was to explore the feasibility and performance of a multi-sectored tubular array transurethral ultrasound applicator for prostate thermal therapy, with potential to provide dynamic angular and length control of heating under MR guidance without mechanical movement of the applicator. Test configurations were fabricated, incorporating a linear array of two multi-sectored tubular transducers (7.8-8.4 MHz, 3 mm OD, 6 mm length), with three 120 degrees independent active sectors per tube. A flexible delivery catheter facilitated water cooling (100 ml min(-1)) within an expandable urethral balloon (35 mm long x 10 mm diameter). An integrated positioning hub allows for rotating and translating the transducer assembly within the urethral balloon for final targeting prior to therapy delivery. Rotational beam plots indicate approximately 90 degrees-100 degrees acoustic output patterns from each 120 degrees transducer sector, negligible coupling between sectors, and acoustic efficiencies between 41% and 53%. Experiments were performed within in vivo canine prostate (n = 3), with real-time MR temperature monitoring in either the axial or coronal planes to facilitate control of the heating profiles and provide thermal dosimetry for performance assessment. Gross inspection of serial sections of treated prostate, exposed to TTC (triphenyl tetrazolium chloride) tissue viability stain, allowed for direct assessment of the extent of thermal coagulation. These devices created large contiguous thermal lesions (defined by 52 degrees C maximum temperature, t43 = 240 min thermal dose contours, and TTC tissue sections) that extended radially from the applicator toward the border of the prostate (approximately15 mm) during a short power application (approximately 8-16 W per active sector, 8-15 min), with approximately 200 degrees or 360 degrees sector coagulation demonstrated depending upon the activation scheme. Analysis of transient temperature profiles indicated progression of lethal temperature and thermal dose contours initially centered on each sector that coalesced within approximately 5 min to produce uniform and contiguous zones of thermal destruction between sectors, with smooth outer boundaries and continued radial propagation in time. The dimension of the coagulation zone along the applicator was well-defined by positioning and active array length. Although not as precise as rotating planar and curvilinear devices currently under development for MR-guided procedures, advantages of these multi-sectored transurethral applicators include a flexible delivery catheter and that mechanical manipulation of the device using rotational motors is not required during therapy. This multi-sectored tubular array transurethral ultrasound technology has demonstrated potential for relatively fast and reasonably conformal targeting of prostate volumes suitable for the minimally invasive treatment of BPH and cancer under MR guidance, with further development warranted.

Transurethral microwave thermotherapy: from evidence-based medicine to clinical practice

PURPOSE OF REVIEW

The aim of this article is to provide new clinical data on transurethral microwave thermotherapy, evaluate it in the perspective of evidence-based guidelines and daily practice and investigate the driving forces that determine the current position of thermotherapy for the management of benign prostatic obstruction.

RECENT FINDINGS

Recent studies have provided significant evidence regarding the efficacy, safety and durability of thermotherapy. Updated evidence-based clinical guidelines on the management of patients with benign prostatic obstruction have been made available. Surveys have evaluated the acceptance of transurethral microwave thermotherapy from the urological community. In addition, several studies have made major contributions to our knowledge of the translation of evidence to daily practice.

SUMMARY

The range of therapeutic options for benign prostatic obstruction continues to widen creating the need for clarity in selection and application of these treatments. High-quality data on transurethral microwave thermotherapy have been published and integrated into clinical guidelines. Considerations on the implementation of guidelines to clinical practice, emergence of new treatments, shift of benign prostatic obstruction therapy, economics and the increasing need to treat patients with different clinical profile during the last decade seem to affect the position of transurethral microwave thermotherapy in the armamentarium of a urological centre. Into this frame, transurethral microwave thermotherapy tailored to selective cases seems to remain an attractive option.

Treatment Characteristics and Inherent Prostatic Features Do Not Predict Patient Outcome after High-Energy Transurethral Thermotherapy: A Prospective Study of ProstaLund Feedback Treatment™

PURPOSE

To determine whether treatment characteristics, intrinsic prostatic factors, and clinical parameters predict the outcome in patients treated with high-energy transurethral microwave thermotherapy (HE-TUMT).

PATIENTS AND METHODS

A series of 48 consecutive patients, 28 with an indwelling catheter, underwent ProstaLund Feedback Treatment (PLFT). The 12-month International Prostate Symptom Score response rate (IPSS < or = 7 or > or =50% improvement), peak flow rate response rate (Q(max) > or = 15 mL/sec or > or =50% improvement), and bladder outflow obstruction index response rate (BOOI <40) were correlated with treatment characteristics such as duration, average intraprostatic temperature, time with therapeutic intraprostatic temperatures (>45 degrees C), average intraprostatic blood flow, consumed energy, and recorded prostate mass destruction. Baseline parameters such as age, serum prostate specific antigen concentration, prostate volume, and pretreatment IPSS, quality of life (QOL), Q(max), postvoiding residual urine volume (PVR), and BOOI were included in the logistic regression analysis.

RESULTS

Treatment characteristics did not discriminate responders and nonresponders to HE-TUMT. For the patients without a catheter, the IPSS response (75%) was predicted by higher pretreatment IPSS (P = 0.041; relative risk [RR] = 3.4) and higher pretreatment PVR (P = 0.026; RR = 1.1). The Q(max) response (85%) was predicted by higher grades of pretreatment obstruction (P = 0.009; RR = 1.02). The BOOI response (60%) was not related to any of the factors tested. For the patients with a catheter, no outcome predictors could be identified.

CONCLUSIONS

According to our results, the intraprostatic temperature, the duration of intraprostatic temperatures in the therapeutic range, and the pattern of blood flow did not predict HE-TUMT outcome. Treatment duration, consumed energy, and the magnitude of tissue necrosis did not translate into clinical efficacy. Clinical parameters were important predictors of outcome in patients not in retention.

Interstitial temperature mapping during Prolieve transurethral microwave treatment: Imaging reveals thermotherapy temperatures resulting in tissue necrosis and patent prostatic urethra

OBJECTIVES

Temperature mapping of the prostate during transurethral microwave thermotherapy and imaging of the resultant zones of tissue necrosis have been previously performed using several commercial systems. This study was performed using the Prolieve Thermodilatation System, which simultaneously compresses the prostate with a 46F balloon circulating heated fluid and delivering microwave energy into the prostate.

METHODS

Interstitial temperature mapping during Prolieve treatment was performed on 10 patients with benign prostatic hyperplasia using 24 temperature sensors arrayed throughout the prostate. Voiding cystourethrograms were performed on 3 additional patients treated without temperature mapping to document the patency of the prostatic urethra 1 hour after treatment. Gadolinium-enhanced magnetic resonance imaging studies were performed on all patients 1 week after treatment to determine the extent and pattern of tissue necrosis resulting from transurethral microwave thermotherapy.

RESULTS

Interstitial temperature mapping found that the heating pattern generated by the Prolieve system created average peak temperatures of 51.8 degrees C an average of 7 mm away from the prostatic urethra. These temperatures were greater near the bladder neck and mid-gland than toward the prostatic apex. Subtherapeutic temperatures were seen adjacent to the urethra, consistent with the viable tissue seen on gadolinium-enhanced magnetic resonance imaging sequences. Magnetic resonance imaging also revealed necrotic zones that were consistent with sustained temperatures greater than 45 degrees C. Voiding cystourethrograms showed widely patent prostatic urethras 1 hour after treatment.

CONCLUSIONS

Transurethral microwave thermotherapy with the Prolieve Thermodilatation System produced sustained therapeutic temperatures that resulted in tissue necrosis while maintaining viable tissue surrounding a temporarily dilated prostatic urethra.