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Title: Model-based feasibility assessment and evaluation of prostate hyperthermia with a commercial MR-guided endorectal HIFU ablation array

Purpose: Feasibility of targeted and volumetric hyperthermia (40–45 °C) delivery to the prostate with a commercial MR-guided endorectal ultrasound phased array system, designed specifically for thermal ablation and approved for ablation trials (ExAblate 2100, Insightec Ltd.), was assessed through computer simulations and tissue-equivalent phantom experiments with the intention of fast clinical translation for targeted hyperthermia in conjunction with radiotherapy and chemotherapy. Methods: The simulations included a 3D finite element method based biothermal model, and acoustic field calculations for the ExAblate ERUS phased array (2.3 MHz, 2.3 × 4.0 cm{sup 2}, ∼1000 channels) using the rectangular radiator method. Array beamforming strategies were investigated to deliver protracted, continuous-wave hyperthermia to focal prostate cancer targets identified from representative patient cases. Constraints on power densities, sonication durations and switching speeds imposed by ExAblate hardware and software were incorporated in the models. Preliminary experiments included beamformed sonications in tissue mimicking phantoms under MR temperature monitoring at 3 T (GE Discovery MR750W). Results: Acoustic intensities considered during simulation were limited to ensure mild hyperthermia (T{sub max} < 45 °C) and fail-safe operation of the ExAblate array (spatial and time averaged acoustic intensity I{sub SATA} < 3.4 W/cm{sup 2}). Tissue volumes with therapeutic temperature levels (T > 41 °C) weremore » estimated. Numerical simulations indicated that T > 41 °C was calculated in 13–23 cm{sup 3} volumes for sonications with planar or diverging beam patterns at 0.9–1.2 W/cm{sup 2}, in 4.5–5.8 cm{sup 3} volumes for simultaneous multipoint focus beam patterns at ∼0.7 W/cm{sup 2}, and in ∼6.0 cm{sup 3} for curvilinear (cylindrical) beam patterns at 0.75 W/cm{sup 2}. Focused heating patterns may be practical for treating focal disease in a single posterior quadrant of the prostate and diffused heating patterns may be useful for heating quadrants, hemigland volumes or even bilateral targets. Treatable volumes may be limited by pubic bone heating. Therapeutic temperatures were estimated for a range of physiological parameters, sonication duty cycles and rectal cooling. Hyperthermia specific phasing patterns were implemented on the ExAblate prostate array and continuous-wave sonications (∼0.88 W/cm{sup 2}, 15 min) were performed in tissue-mimicking material with real-time MR-based temperature imaging (PRFS imaging at 3.0 T). Shapes of heating patterns observed during experiments were consistent with simulations. Conclusions: The ExAblate 2100, designed specifically for thermal ablation, can be controlled for delivering continuous hyperthermia in prostate while working within operational constraints.« less
Authors:
; ;  [1] ;  [2] ; ; ;  [3] ;  [4]
  1. Thermal Therapy Research Group, Radiation Oncology, University of California San Francisco, 1600 Divisadero Street, Suite H-1031, San Francisco, California 94143 (United States)
  2. Department of Electrical and Computer Engineering, Kansas State University, 2077 Rathbone Hall, Manhattan, Kansas 66506 (United States)
  3. Department of Radiology and Biomedical Imaging, University of California San Francisco, 505 Parnassus Avenue, San Francisco, California 94143 (United States)
  4. Department of Radiology, Stanford University, 1201 Welch Road, Stanford, California 94305 (United States)
Publication Date:
OSTI Identifier:
22250971
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 3; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ABLATION; ANIMAL TISSUES; BEAMS; CHEMOTHERAPY; COMPUTER CODES; COMPUTERIZED SIMULATION; CYLINDRICAL CONFIGURATION; FINITE ELEMENT METHOD; HEATING; HYPERTHERMIA; LIMITING VALUES; NEOPLASMS; PHANTOMS; POWER DENSITY; PROSTATE; RADIOTHERAPY; RECTUM; SKELETON; TEMPERATURE MONITORING