MR Thermometry-guided Prostate Hyperthermia with Real-time Ultrasound Beamforming and Power Control

Eugene Ozhinsky¹, Vasant A. Salgaonkar², Chris J. Diederich², and Viola Rieke¹

¹Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, ²Radiation Oncology, University of California San Francisco, San Francisco, CA, United States

Synopsis

We have developed and evaluated a real-time MR thermometry-guided system for acoustic power output and beam pattern control for prostate hyperthermia therapy. It was designed to be integrated with a commercial focused ultrasound ablation system and supports real-time ultrasound phase pattern switching and MR thermometry for monitoring and automated power adjustment.

Introduction

Hyperthermia (HT, 40-45°C, 30-60 min) has been combined successfully with several cancer treatment modalities, such as radiation, chemotherapy and drug delivery (1,2) to enhance treatment efficacy. Clinical studies have demonstrated feasibility of safe application of prostate hyperthermia with endorectal ultrasound applicators (3). The goal of this project was to implement an MR thermometry-guided hyperthermia that allowed to change both shape and acoustic power of the beam in real time.

Methods

The real-time thermometry application (fig. 1) was developed for the RTHawk real-time MRI system (HeartVista, Inc., Menlo Park, CA), connected to a 3T MR scanner (GE Healthcare, Waukesha, WI) and the ExAblate 2100 prostate array (InSightec, Haifa, Israel). The application included an SPGR pulse sequence (TE = 13.4 ms, FOV = 28-32 cm, 3 s/slice), a real-time PRFS thermometry reconstruction pipeline and a custom interface for data visualization and prescription. The system provided for interleaved simultaneous acquisition of multiple slices at different orientations. Temperature measurement was implemented using user-adjustable elliptical ROIs.

The beam controller module was implemented for the RTHawk MR Thermometry application (fig. 1,2). It featured a proportional integral feedback controller for automated beam power adjustment and an ability to switch between up to 4 transducer phasing patters (single focus at 60 mm depth, simultaneous 4 point focusing with the focal distance of 60 mm and spread of 5, 10 and 15 mm).

To interface with vendor ultrasound control software, a Control Proxy Server application was developed. It accepted connections from the beam controller module over the local area network and translated commands into calls of the vendor-provided software interface.

The system was evaluated in experiments with a tissue mimicking phantom for prolonged exposures at max. electrical power of 10 W.

Results and Discussion

Fig. 3 (d-f) shows MR thermometry images during heating with the three phasing patterns. We were able to achieve the heating patterns that closely resembled the simulated beam shapes (fig. 3, a-c). Changing the spread of focal points in real-time allowed to adjust the beam shape and could be used to achieve the desired heating pattern for a particular patient anatomy and tissue thermal conductivity.

One limitation of the current technique is a limited range of beam depth due to the small number of discrete phase values, supported by the phased array transducer. Future work will focus on implementing phased patterns for different treatment scenarios (4) and in-vivo validation.

In conclusion, we have implemented a real-time MR thermometry-guided ultrasound beam control system for long duration prostate hyperthermia therapy and validated it in phantom experiments.

Acknowledgements

We would like to thank Benny Assif, Alex Kavushansky, Yerucham Shapira (Insightec, Inc.) for technical assistance with this project. This work was supported by Focused Ultrasound Foundation, NIH R01CA12276, R01CA111981, R00HL097030, UCSF-RAP.

References

1. Wust P, Hildebrandt B, Sreenivasa G, Rau B, Gellermann J, Riess H, Felix R, Schlag PM. Hyperthermia in combined treatment of cancer. The Lancet Oncology 2002;3(8):487-497.

2. Ponce AM, Vujaskovic Z, Yuan F, Needham D, Dewhirst MW. Hyperthermia mediated liposomal drug delivery. International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group 2006;22(3):205-213.

3. Hutchinson E, Dahleh M, Hynynen K. The feasibility of MRI feedback control for intracavitary phased array hyperthermia treatments. International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group 1998;14(1):39-56.

4. Salgaonkar VA, Prakash P, Rieke V, Ozhinsky E, Plata J, Kurhanewicz J, Hsu IC, Diederich CJ. Model-based feasibility assessment and evaluation of prostate hyperthermia with a commercial MR-guided endorectal HIFU ablation array. Med Phys 2014;41(3):033301.

Figures

Fig. 1. User interface of the MR thermometry application with beam control module (bottom right). The software allows to monitor up to three slices in arbitrary orientations.

Fig. 2. Diagram of the MR Thermometry-based ultrasound beam control system.

Fig. 3. Simulated simultaneous focus acoustic pattern with focal depth of 60 mm and spread of 5mm (a) and 15 mm (b); c: single focus at 60 mm; d-f: real-time MR thermometry images while heating with patterns above.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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