Dana L. Deardorff

Combination of transurethral and interstitial ultrasound applicators for high-temperature prostate thermal therapy

The purpose of this study was to determine the feasibility of using a transurethral ultrasound applicator in combination with implantable ultrasound applicators for inducing thermal coagulation and necrosis of localized cancer lesions or benign disease within the prostate gland. The potential to treat target zones in the anterior and lateral portions of the prostate with the angularly directive transurethral applicator, while simultaneously treating regions of extracapsular extension and zones in the posterior prostate with the directive implantable applicators in combination with a rectal cooling bolus, is evaluated. Biothermal computer simulations, acoustic characterizations, and in vivo thermal dosimetry experiments with canine prostates were used to evaluate the performance of each applicator type and combinations thereof. Simulations have demonstrated that transurethral applicators with 180-270° acoustic active zones can direct therapeutic heating patterns to the anterior and lateral prostate, implantable needles can isolate heating to the posterior gland while avoiding rectal tissue, and that the combination of applicators can be used to produce conformal heating to the whole gland. Single implantable applicators (1.8mm ODx10mm long, ∼180° active sector, ∼7MHz, direct-coupled type) produced directional thermal lesions within in vivo prostate, with temperatures >50°C extending more than 10mm radially after 10-15min. Combination of interstitial applicators (1-2) and a transurethral applicator (3-2.5mm ODx6 mm long, 180° active sector, 6.8MHz, 6 mm OD delivery catheter) produced conforming temperature distributions (48-85°C) and zones of acute thermal damage within 15min. The preliminary results of this investigation demonstrate that implantable directional ultrasound applicators, in combination with a transurethral ultrasound applicator, have the potential to provide thermal coagulation and necrosis of small or large regions within the prostate gland, while sparing thermally sensitive rectal tissue.

Axial control of thermal coagulation using a multi-element interstitial ultrasound applicator with internal cooling

A multi-element, direct-coupled ultrasound (US) applicator with internal water cooling was investigated for axial control of interstitial thermal coagulation. A prototype implantable applicator was constructed with a linear array of three tubular PZT ultrasound transducers (each 2.5 mm OD, 10 mm length, 360/spl deg/ emittance). Acoustic beam distributions from each element were measured and found to be collimated within the transducer length. The internally cooled applicator could sustain high levels of applied power to each transducer (0 to 40 W) and maintain acceptable applicator surface temperatures (<100/spl deg/C). Thermal performance of the applicator was investigated through heating trials in vivo (porcine thigh muscle and liver) and in vitro (bovine liver). The radial depth of thermal lesions produced was dependent on the applied power and sonication time and was controlled independently with power levels to each transducer element. With 18 W per element (applied electrical power) for 3 min, cylindrical thermal lesions were produced with a diameter of /spl sim/3 cm and a length ranging from 1.2 cm (with one element) to 3.5 cm (three elements). Higher powers (24 to 30 W) for 3 to 5 min provided increased depths of coagulation (/spl sim/4 cm diameter lesions). Analysis of axial lesion shapes demonstrated that individual variation of power to each transducer element provided control of axial heating and depth of coagulation (for custom lesion shapes); lesion lengths corresponded to the number of active transducers. This ability to control the heating distribution dynamically along the length of the applicator has potential for improved target localization of thermal coagulation and necrosis in high temperature thermal therapy.

Ultrasound applicators with internal water-cooling for high-powered interstitial thermal therapy

Internal water-cooling of direct-coupled ultrasound (US) applicators for interstitial thermal therapy (hyperthermia and coagulative thermal therapy) was investigated. Implantable applicators were constructed using tubular US sources (360 angular acoustic emittance, /spl sim/7 MHz) of 10 mm length and 1.5, 1.8, 2.2, and 2.5 mm outer diameter (OD). Directional applicators were also constructed using 2.2 mm OD tubes sectored to provide active acoustic sectors of 90/spl deg/ and 200/spl deg/. A water-cooling mechanism was integrated within the inner lumen of the applicator to remove heat from the inner transducer surface. High levels of convective heat transfer (2100-3800 W/m/sup 2/K) were measured for practical water flow rates of 20-80 mL/min. Comparative acoustic measurements demonstrated that internal water-cooling did not significantly degrade the acoustic intensity or beam distribution of the US transducers. Water-cooling allowed substantially higher levels of applied electrical power (>45 W) than previous designs (with air-cooling or no cooling), without detriment to the applicators. High temperature heating trials performed with these applicators in vivo (porcine liver and thigh muscle) and in vitro (bovine liver) showed improved thermal penetration and coagulation. Radial depth of coagulation from the applicator surface ranged from 12 to 20 mm for 1-5 min of sonication with 28-W applied power. Higher powers (41 W) demonstrated increased coagulation depths (/spl sim/9 mm) at shorter times (15 s). Thermal lesion dimensions (angular and axial expanse) produced with directional applicators were controlled and directed, and corresponded to the active zone of the transducer. These characteristic lesion shapes were also generally unchanged with different sonication times and power, and were found to be consistent with previous coagulation studies using air-cooled applicators. The implementation of water-cooling is a significant advance for the application of ultrasound interstitial thermal therapy (USITT), providing greater treatment volumes, shorter treatment times, and the potential for treatment of highly perfused tissue with shaped lesions.

Control of interstitial thermal coagulation: comparative evaluation of microwave and ultrasound applicators.

This study presents a comparative evaluation of the control of heating and thermal coagulation with microwave (MW) and ultrasound (US) interstitial applicators. Helical coil MW antennas (17 mm and 25 mm length radiating antennae) were tested using an external implant catheter (2.2 mm o.d.) with water-cooling. US applicators with tubular transducers (2.2 and 2.5 mm o.d., 10 mm length, single-element and 3-element) were utilized with a direct-coupled configuration and internal water-cooling. Measurements of E-field distributions (for MW) and acoustic beam distributions (for US) were used to characterize the applicator energy output. Thermal performance was evaluated through multiple heating trials in vitro (bovine liver) and in vivo (porcine thigh muscle and liver) at varied levels of applied power (20-40 W for microwave, 15-35 W for ultrasound) and heating times (0.5-5 min). Axial temperature distributions in the tissue were recorded during heating, and dimensions of the resulting lesions of thermal coagulation were measured. Both MW and US applicators produced large volumes of tissue coagulation ranging from 8 to 20 cm3 with singular heating times of 5 min. Radial depth of lesions for both MW and US applicators increased with heating duration and power levels, though US produced notably larger lesion diameters (30-42 mm for US vs 18-26 mm for MW, 5 min heating). Characteristic differences between the applicators were observed in axial energy distribution, tissue temperatures, and thermal lesion shapes. MW lesions increased significantly in axial dimensions (beyond the active applicator length) as applied power level and/or heating duration was increased, and lesion shapes were generally not uniform. US provided greater control and uniformity of heating, with energy deposition and axial extent of thermal lesions corresponding to the length of the active transducer(s). The improved ability to control the extent of thermal coagulation demonstrated by the US applicators provides greater potential to target a specific region of tissue.

Angular directivity of thermal coagulation using air-cooled direct-coupled interstitial ultrasound applicators

The performance characteristics and thermal coagulation of tissue produced by directional air-cooled, direct-coupled interstitial ultrasound (US) applicators were evaluated. Prototype applicators (2.2 mm o.d.) were constructed using cylindrical transducers sectored into angular active zones of 90 degrees, 200 degrees, 270 degrees, and 360 degrees. Acoustic characterization of the applicators showed the beam output to be angularly directed from the active sector of the transducer and collimated within the axial extent. Empirical determination of the average convective heat transfer coefficient, resulting from airflow cooling the inner surface of the transducer, showed significantly high levels of transfer (> 700 W m(-2) degrees C(-1)) with a flow rate of 5.6 L min(-1). Thermal performance of the applicators was characterized through high temperature heating in vivo (porcine thigh muscle, 11 trials) and in vitro (bovine liver, 46 trials). Results demonstrated directional coagulation of tissue, with good correlation between the angular extent of the lesions and the active acoustic sector. Radial depth of coagulation with a 200 degrees applicator extended 8-17 mm, with a heating time of 1-10 min, respectively. Angular and axial lesion shape remained similar over the course of 1-10 min heating trials. Implementation of air-cooling within direct-coupled interstitial US applicators provided enhanced directivity of heating in angular and axial dimensions, and significantly increased the power handling and radial depth of tissue coagulation.

Air-cooling of direct-coupled ultrasound applicators for interstitial hyperthermia and thermal coagulation

The feasibility of using air-cooling to improve the thermal penetration of direct-coupled interstitial ultrasound (US) applicators was investigated using biothermal simulations, bench experiments, phantom testing, and in vivo thermal dosimetry. Two applicator configurations using tubular US transducers were constructed and tested. The first design, intended for simultaneous thermobrachy-therapy, utilizes a 2.5 mm OD transducer with a central lumen to accommodate a radiation source from remote afterloaders. The second applicator consists of a 2.2 mm OD transducer designed for coagulative thermal therapy. Both designs provide cooling of the inner transducer surface by the counterflow of chilled air or CO2 gas through the annulus of the enclosed applicator. The average convective heat transfer (ha) associated with each applicator was determined empirically from curve-fits of radial steady-state temperatures measured in a tissue-mimicking phantom. High levels of convective heat transfer (ha > 500 W m-2 degrees C-1) were demonstrated in both designs at relatively low flow rates (< 5 L min-1). Transient and steady-state radial heating profiles were also measured in vivo (pig thigh muscle) with and without cooling. The therapeutic radius for hyperthermia (41-45 degrees C) was extended from 5-6 mm (without cooling) to 11-19 mm with air-cooling (4.8 L min-1, airflow 10 degrees C), effectively doubling and tripling the thermal penetration in vivo. Similar improvements were demonstrated at higher temperatures with the thermal coagulation applicator. Biothermal simulations, which modeled the physical, thermal, and acoustic parameters of the air-cooled applicator and surrounding tissue, were also used to investigate potential improvements in heating patterns. The simulated radial heating profiles with transducer cooling demonstrated significantly enhanced thermal penetration over the experimental range of convective transfer, and also agreed with in vivo results. These theoretical and experimental results clearly show air-cooling controls the transducer surface temperature, significantly increases thermal penetration, and produces a greater treatment volume for direct-coupled US applicators in hyperthermia and thermal coagulation.

Ultrasound interstitial thermal therapy (USITT) in the prostate

This research represents an experimental investigation of the use of interstitial catheter-cooled ultrasound applicators in various treatment strategies for the management of localized prostate cancer and benign prostatic hyperplasia. The anticipated clinical approaches under consideration were: (1) Ultrasound Interstitial Thermal therapy (USITT) alone for treatment of the whole gland, (2) high dose rate (HDR) brachytherapy with USITT to treat local recurrences or extracapsular extensions of the disease, and (3) sequence HDR brachytherapy and hyperthermia. Directional multielement catheter-cooled ultrasound applicators were fabricated using cylindrical piezoceramic transducers which can be inserted into 13 or 14 gage catheters. The applicators were characterized through measurements of acoustic power output, and beam profile distributions in degassed water. Thermal lesion formation studies were performed in an in vitro setup using fresh beef muscle. Various implant strategies were evaluated for the ability to control the temperature distribution within a pre-determined volume of tissue. Lesions extending more than 15 mm from the applicator surface were generated within 5 minutes of heating. Preliminary results from this study demonstrate the versatility of catheter-cooled interstitial ultrasound applicators, and their potential to provide controlled thermal therapy in the prostate.

Combination of implantable and transurethral ultrasound applicators for prostate thermal therapy

This preliminary investigation demonstrates that using implantable ultrasound applicators (with energy directed away from the rectum and nontargeted tissue) in combination with a directional transurethral ultrasound applicator have potential to provide controlled thermal coagulation and necrosis of small or large regions within the prostate gland, while sparing thermally sensitive rectal tissue.

Ultrasound applicators with internal cooling for interstitial thermal therapy

The use of internally-cooled, direct-coupled interstitial ultrasound applicators as a means of providing controlled and directed thermal therapy was investigated. Applicators were constructed using tubular ultrasound sources (1.5 - 2.5 mm OD) with active acoustic zones of 90 degree(s), 200 degree(s), 270 degree(s), and 360 degree(s) (single and multiple transducers). Cooling of the inner transducer surface was accomplished by the flow of chilled air or an integrated water mechanism. Thermal performance of the applicators was characterized through high temperature heating trials in vivo (porcine thigh muscle and liver) and in vitro (bovine liver). Both air-cooled and water-cooled applicators produced well- defined angular directional heating, with coagulated zones corresponding to the active sector of the transducer. Axial collimation and control of heating along the length of the applicator was also demonstrated using multiple transducer elements. Thermal penetration and extent of coagulation was reproducible and controlled with sonication time and power, extending radially 12 - 22 mm for 1 - 5 minutes. Directly of lesion shapes (both angular and axial) was found to remain characteristically similar at different heating times. This enhanced thermal penetration and improved control of directional heating with internal cooling shows great potential for treatment of localized tumors in prostate, brain, and liver.

Interstitial ultrasound applicators with internal cooling for controlled high temperature thermal therapy

The use of internally-cooled, direct-coupled interstitial ultrasound applicators as a means of providing controlled and directed high temperature thermal therapy was investigated. Prototype applicators were constructed using tubular ultrasound sources (1.5-2.5 mm OD) with transducers sectored for 90/spl deg/, 200/spl deg/, and 360/spl deg/ active acoustic zones. Effective cooling of the transducer surface was accomplished by the internal flow of chilled air or an integrated water mechanism. Thermal performance of the applicators was characterized through high temperature heating trials in-vivo (porcine thigh muscle and liver) and in-vitro (bovine liver) with varied sonication time and power. In general, internal cooling provided greatly enhanced thermal penetration and improved control of directional heating. This demonstrated ability to control and direct the extent of thermal coagulation shows great potential for treatment of localized tumors in sites such as prostate, brain, and liver.