A clinical treatment delivery platform has been developed and is being evaluated in a clinical pilot study for providing
3D controlled hyperthermia with catheter-based ultrasound applicators in conjunction with high dose rate (HDR)
brachytherapy. Catheter-based ultrasound applicators are capable of 3D spatial control of heating in both angle and
length of the devices, with enhanced radial penetration of heating compared to other hyperthermia technologies.
Interstitial and endocavity ultrasound devices have been developed specifically for applying hyperthermia within HDR
brachytherapy implants during radiation therapy in the treatment of cervix and prostate. A pilot study of the
combination of catheter based ultrasound with HDR brachytherapy for locally advanced prostate and cervical cancer has
been initiated, and preliminary results of the performance and heating distributions are reported herein. The treatment
delivery platform consists of a 32 channel RF amplifier and a 48 channel thermocouple monitoring system. Controlling
software can monitor and regulate frequency and power to each transducer section as required during the procedure.
Interstitial applicators consist of multiple transducer sections of 2-4 cm length × 180 deg and 3-4 cm × 360 deg. heating
patterns to be inserted in specific placed 13g implant catheters. The endocavity device, designed to be inserted within a
6 mm OD plastic tandem catheter within the cervix, consists of 2-3 transducers × dual 180 or 360 deg sectors. 3D
temperature based treatment planning and optimization is dovetailed to the HDR optimization based planning to best
configure and position the applicators within the catheters, and to determine optimal base power levels to each
transducer section. To date we have treated eight cervix implants and six prostate implants. 100 % of treatments
achieved a goal of >60 min duration, with therapeutic temperatures achieved in all cases. Thermal dosimetry within the
hyperthermia target volume (HTV) and clinical target volume (CTV) are reported. Catheter-based ultrasound
hyperthermia with HDR appears feasible with therapeutic temperature coverage of the target volume within the prostate
or cervix while sparing surrounding more sensitive regions.
Steerability in percutaneous medical devices is highly desirable, enabling a needle or needle-like instrument to avoid
sensitive structures (e.g. nerves or blood vessels), access obstructed anatomical targets, and compensate for the
inevitable errors induced by registration accuracy thresholds and tissue deformation during insertion. Thus, mechanisms
for needle steering have been of great interest in the engineering community in the past few years, and several have been
proposed. While many interventional applications have been hypothesized for steerable needles (essentially anything
deliverable via a regular needle), none have yet been demonstrated as far as the authors are aware. Instead, prior studies
have focused on model validation, control, and accuracy assessment. In this paper, we present the first integrated
steerable needle-interventional device. The ACUSITT integrates a multi-tube steerable Active Cannula (AC) with an
Ultrasonic Interstitial Thermal Therapy ablator (USITT) to create a steerable percutaneous device that can deliver a
spatially and temporally controllable (both mechanically and electronically) thermal dose profile. We present our initial
experiments toward applying the ACUSITT to treat large liver tumors through a single entry point. This involves
repositioning the ablator tip to several different locations, without withdrawing it from the liver capsule, under 3D
Ultrasound image guidance. In our experiments, the ACUSITT was deployed to three positions, each 2cm apart in a conical pattern to demonstrate the feasibility of ablating large liver tumors 7cm in diameter without multiple parenchyma punctures.
An intracavitary hyperthermia applicator for targeted heat delivery to the cervix was developed based on a linear array of
sectored tubular ultrasound transducers that provides truly 3-D heating control (angular and along the length). A central
conduit can incorporate an HDR source for sequential or simultaneous delivery of heat and radiation. Hyperthermia
treatment volumes were determined from brachytherapy treatment planning data and used as a basis for biothermal
simulations analyzing the effects of device parameters, tissue properties, and catheter materials on heating patterns.
Devices were then developed with 1-3 elements at 6.5-8 MHz with
90-180° sectors and a 15-35 mm heating length,
housed within a 6-mm diameter water-cooled PET catheter. Directional heating from sectored transducers could extend
lateral penetration of therapeutic heating (41°C) >2 cm while maintaining rectum and bladder temperatures within 12
mm below thermal damage thresholds. Imaging artifacts were evaluated with standard CT, cone beam CT, and MR
images. MR thermal imaging was used to demonstrate shaping of heating profiles in axial and coronal slices with
artifact <2 mm from the device. The impact of the high-Z applicator materials on the HDR dose distribution was
assessed using a well-type ionization chamber and was found to be less than 6% attenuation, which can readily be
accounted for with treatment planning software. The intrauterine ultrasound device has demonstrated potential for 3-D
conformal heating of clinical tumors in the delivery of targeted hyperthermia in conjunction with brachytherapy to the
cervix.
KEYWORDS: Francium, Ultrasonography, Thermometry, Amplifiers, Control systems, Transducers, High dynamic range imaging, Computing systems, Temperature metrology, Human-machine interfaces
A clinical treatment delivery platform has been developed for providing 3D controlled hyperthermia with catheter-based
ultrasound applicators in conjunction with high dose rate (HDR) brachytherapy. This integrated system consists of
hardware and software components required for thermal therapy delivery, treatment monitoring and control, and realtime
and post-treatment analysis; and interstitial and endocavity ultrasound heating applicators. Hardware includes a
32-channel RF amplifier with independent power (0-25 W) and frequency (5-10 MHz) control for ultrasound power
delivery and a 48-channel thermometry system compatible with 0.4 mm OD multi-sensor thermocouple probes.
Software graphical user interfaces (GUI) are used to monitor and control both the amplifier and the thermometry system.
The amplifier GUI controls, monitors, and records individual channel frequency and power values in real-time; the
thermometry GUI monitors and records temperature and thermal dose values in real-time, as well as displaying and
allowing dynamic control for temperature and thermal dose target thresholds. The thermometry GUI also incorporates
registration of thermocouple positions relative to target anatomy and applicator transducers based on HDR planning
tools (CT/MRI/US overlays) for improved treatment control and documentation. The interstitial (2.4 mm) and
endocavity (6 mm) ultrasound hyperthermia applicators are composed of linear arrays of 1-4 tubular piezoceramic
transducers - sectored at 90°, 180°, 270°, and 360° for single or dual directional heating patterns - that are compatible
with plastic implant catheters. QA techniques specific to these catheter-based ultrasound applicators have been devised
and implemented, and include rotational beam plots and dynamic force balance efficiency measurements, which are
critical to establish applicator performance. A quality assurance test matrix has been devised and used to evaluate and
characterize all components of this system prior to clinical implementation.
Uterine myomas (fibroids) are the most common pelvic tumors occurring in women, and are the leading cause of
hysterectomy. Symptoms can be severe, and traditional treatments involve either surgical removal of the uterus
(hysterectomy), or the fibroids (myomectomy). Interstitial ultrasound technologies have demonstrated potential for
hyperthermia and high temperature thermal therapy in the treatment of benign and malignant tumors. These ultrasound
devices offer favorable energy penetration allowing large volumes of tissue to be treated in short periods of time, as well
as axial and angular control of heating to conform thermal treatment to a targeted tissue, while protecting surrounding
tissues from thermal damage. The goal of this project is to evaluate interstitial ultrasound for controlled thermal
coagulation of fibroids. Multi-element applicators were fabricated using tubular transducers, some of which were
sectored to produce 180° directional heating patterns, and integrated with water cooling. Human uterine fibroids were
obtained after routine myomectomies, and instrumented with thermocouples spaced at 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 cm
from the applicator. Power levels ranging from 8-15 W per element were applied for up to 15 minute heating periods.
Results demonstrated that therapeutic temperatures >50° C and cytotoxic thermal doses (t43) extended beyond 2 cm
radially from the applicator (>4 cm diameter). It is anticipated that this system will make a significant contribution
toward the treatment of uterine fibroids.
Four types of transurethral applicators were devised for thermal ablation of prostate combined with MR thermal
monitoring: sectored tubular transducer devices with directional heating patterns; planar and curvilinear devices with
narrow heating patterns; and multi-sectored tubular devices capable of dynamic angular control without applicator
movement. These devices are integrated with a 4 mm delivery catheter, incorporate an inflatable cooling balloon (10
mm OD) for positioning within the prostate and capable of rotation via an MR-compatible motor. Interstitial devices
(2.4 mm OD) have been developed for percutaneous implantation with directional or dynamic angular control. In vivo
experiments in canine prostate under MR temperature imaging were used to evaluate the heating technology and develop
treatment control strategies. MR thermal imaging in a 0.5 T interventional MRI was used to monitor temperature and
thermal dose in multiple slices through the target volume. Sectored tubular, planar, and curvilinear transurethral
devices produce directional coagulation zones, extending 15-20 mm radial distance to the outer prostate capsule.
Sequential rotation and modulated dwell time can conform thermal ablation to selected regions. Multi-sectored
transurethral applicators can dynamically control the angular heating profile and target large regions of the gland in short
treatment times without applicator manipulation. Interstitial implants with directional devices can be used to effectively
ablate the posterior peripheral zone of the gland while protecting the rectum. The MR derived 52 °C and lethal thermal
dose contours (t43=240 min) allowed for real-time control of the applicators and effectively defined the extent of thermal
damage. Catheter-based ultrasound devices, combined with MR thermal monitoring, can produce relatively fast and
precise thermal ablation of prostate, with potential for treatment of cancer or BPH.
Previous studies have reported the computer modeling, CAD design, and theoretical performance of single and multiple antenna arrays of Dual Concentric Conductor (DCC) square slot radiators driven at 915 and 433 MHz. Subsequently, practical CAD designs of microstrip antenna arrays constructed on thin and flexible printed circuit board (PCB) material were reported which evolved into large Conformal Microwave Array (CMA) sheets that could wrap around the surface of the human torso for delivering microwave energy to large areas of superficial tissue. Although uniform and adjustable radiation patterns have been demonstrated from multiple element applicators radiating into simple homogeneous phantom loads, the contoured and heterogeneous tissue loads typical of chestwall recurrent breast cancer have required additional design efforts to achieve good coupling and efficient heating from the increasingly larger conformal array applicators used to treat large area contoured patient anatomy. Thus recent work has extended the theoretical optimization of DCC antennas to improve radiation efficiency of each individual aperture and reduce mismatch reflections, radiation losses, noise, and cross coupling of the feedline distribution network of large array configurations. Design improvements have also been incorporated into the supporting bolus structure to maintain effective coupling of DCC antennas into contoured anatomy and to monitor and control surface temperatures under the entire array. New approaches for non-invasive monitoring of surface and sub-surface tissue temperatures under each independent heat source are described that make use of microwave radiometry and flexible sheet grid arrays of thermal sensors. Efforts to optimize the clinical patient interface and move from planar rectangular shapes to contoured vest applicators that accommodate entire disease in a larger number of patients are summarized. By applying heat more uniformly to large areas of contoured anatomy, the CMA applicator resulting from these enhancements should expand the number of patients that can benefit from effective heating of superficial disease in combination with radiation or chemotherapy.
Laboratory experiments have shown that thermal enhancement of radiation response increases substantially for higher thermal dose (approaching 100 CEM43) and when hyperthermia and radiation are delivered simultaneously. Unfortunately, equipment capable of delivering uniform doses of heat and radiation simultaneously has not been available to test the clinical potential of this approach. We present recent progress on the clinical implementation of a system that combines the uniform heating capabilities of flexible printed circuit board microwave array applicators with an array of brachytherapy catheters held a fixed distance from the skin for uniform radiation of tissue <1.5 cm deep with a scanning high dose rate (HDR) brachytherapy source. The system is based on the Combination Applicator which consists of an array of up to 32 Dual Concentric Conductor (DCC) apertures driven at 915 MHz for heating tissue, coupled with an array of 1 cm spaced catheters for HDR therapy. Efforts to optimize the clinical interface and move from rectangular to more complex shape applicators that accommodate the entire disease in a larger number of patients are described. Improvements to the system for powering and controlling the applicator are also described. Radiation dosimetry and experimental performance results of a prototype 15 x 15 cm dual-purpose applicator demonstrate dose distributions with good homogeneity under large contoured surfaces typical of diffuse chestwall recurrence of breast carcinoma. Investigations of potential interaction between heat and brachytherapy components of a Combination Applicator demonstrate no perceptible perturbation of the heating field from an HDR source or leadwire, no perceptible effect of a scanning HDR source on fiberoptic thermometry, and <0.5% variation of radiation dose delivered through the CMA applicator. By applying heat and radiation simultaneously for maximum synergism of modalities, this dual therapy system should expand the number of patients that can benefit from effective thermoradiotherapy treatments.
The large variance of survival in the treatment of large superficial tumors indicates that the efficacy of current therapies can be dramatically improved. Hyperthermia has shown significant enhancement of response when used in combination with chemotherapy and/or radiation. Control of temperature is a critical factor for treatment quality (and thus effectiveness), since the response of tumor and normal cells is significantly different over a range of just a few degrees (41-45°). For diffuse spreading tumors, microwave conformal arrays have been shown to be a sound solution to deposit the power necessary to reach the goal temperature throughout the targeted tissue. Continuous temperature monitoring is required for feedback control of power to compensate for physiologic (e.g. blood perfusion and dielectric properties) changes. Microwave radiometric thermometry has been proposed to complement individual fluoroptic probes to non-invasively map superficial and sub-surface temperatures. The challenge is to integrate the broadband antenna used for radiometric sensing with the high power antenna used for power deposition. A modified version of the dual concentric conductor antenna presented previously is optimized for such use. Several design challenges are presented including preventing unwanted radiating modes and thermal and electromagnetic coupling between the two antennas, and accommodating dielectric changes of the target tissue. Advanced 3D and planar 2D simulation software are used to achieve an initial optimized design, focused on maintaining appropriate radiation efficiency and pattern for both heating and radiometry antennas. A cutting edge automated measurement system has been realized to characterize the antennas in a tissue equivalent material and to confirm the simulation results. Finally, the guidelines for further development and improvement of this initial design are presented together with a preliminary implementation of the feedback program to be used to control the temperature distribution in variable, inhomogeneous tissue.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.