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An endocavitary ultrasound applicator has been developed for targeted heat delivery to the cervix. The device has multiple sectored tubular transducers for truly 3-D heating control (angular and along the length) and is integrated with an intracavitary HDR brachytherapy applicator for sequential administration of conformal heat and radiation. Brachytherapy treatment planning data are inspected to determine target thermal treatment volumes. Heat treatments are simulated with an acoustic and biothermal model of cervical tissue. Power control to individual elements and sectors is implemented for global maximum and pilot point control to limit rectum and bladder temperature. A parametric analysis of device parameters, tissue properties, and catheter materials is conducted to assess their effects on heating patterns and inform device development. Acoustic output of all devices was characterized. MR thermal imaging is used to analyze 3-D conformal heating capabilities in ex vivo tissue and compare to theoretical predictions. Devices were fabricated with 1–3 transducers at 6.5–8 MHz with sectors from 90–180° and heating length from 15–35 mm housed within a 6 mm diameter water-cooled PET catheter. Directional heating from sectored transducers can extend lateral penetration of therapeutic heating (41° C)>2 cm while maintaining rectum and bladder temperatures within 12 mm below thermal damage thresholds. MR artifacts extended <2 mm beyond the device and real time thermal imaging was used to guide power selection to shape heating profiles in axial and coronal slices. Endocavitary delivery of ultrasound thermal therapy is feasible and 3-D conformal capabilities will benefit targeted cervical hyperthermia. [ABSTRACT FROM AUTHOR]

Transurethral ultrasound catheter devices in curvilinear configurations are being optimized for improved treatment control and accuracy, reduced treatment times and minimizing surrounding heating of thermally sensitive structures beyond the prostate. A transient acoustic and biothermal model was used to estimate prostate temperature distributions, treatment times and rectal heating for various device configurations and control strategies while accommodating sweeping of curvilinear applicators, power modulation, outer target boundary pilot-point temperature control (sequential rotation) and changes in attenuation with lethal thermal dose. Large prostates can be treated in clinically reasonable times (20–40 min) with low rectal heating if the curvilinear device radius of curvature are increased to 25 mm, device frequency is kept low between 5–6.5 MHz and large device dimensions are chosen (5 X 20 mm) with high maximum allowable temperatures along device length. Pilot-point temperature feedback treatment control can be enhanced with decreased rectal thermal dose by using variable boundary temperatures at the posterior prostate near rectum. [ABSTRACT FROM AUTHOR]

Catheter-based ultrasound applicators have been investigated for delivering hyperthermia and thermal ablation for the treatment of cancer and benign diseases. Technology includes an intrauterine applicator integrated with an HDR ring applicator, interstitial applicators for hyperthermia delivery during brachytherapy, interstitial applicators for tumor ablation, and transurethral devices for conformal prostate ablation. Arrays of multiple sectored tubular transducers have been fabricated for interstitial and intrauterine hyperthermia applicators. High-power interstitial versions have been evaluated for percutaneous implantation with directional or dynamic angular control of thermal ablation. Transurethral applicators include curvilinear transducers with rotational sweeping of narrow heating patterns, and multi-sectored tubular devices capable of dynamic angular control without applicator movement. Performance was evaluated in phantom, excised tissue, in vivo experiments in canine prostate under MR temperature monitoring, clinical hyperthermia, and 3D-biothermal simulations with patient anatomy. Interstitial and intrauterine devices can tailor hyperthermia to large treatment volumes, with multisectored control useful to limit exposure to rectum and bladder. Curvilinear transurethral devices with sequential rotation produce target conforming coagulation zones that can cover either the whole gland or defined focal regions. Multi-sectored transurethral applicators can dynamically control the angular heating profile and target large regions of the prostate without applicator manipulation. High-power interstitial implants with directional devices can be used to effectively ablate defined target regions while avoiding sensitive tissues. MR temperature monitoring can effectively define the extent of thermal damage and provided a means for real-time control of the applicators. In summary, these catheter-based ultrasound devices allow for dynamic control of heating profiles along the length and angular expanse of the applicator during therapy delivery, are amenable to MR monitoring, and provide a minimally-invasive technique for true 3D control of hyperthermia and thermal ablation. [ABSTRACT FROM AUTHOR]