Feasibility of hyperthermia delivery to the prostate with a commercially available MR-guided endorectal ultrasound
(ERUS) phased array ablation system (ExAblate 2100, Insightec, LTD) was assessed through computer simulations and
ex vivo experiments.
The simulations included a 3D FEM-based biothermal model, and acoustic field calculations for the ExAblate phased
array (2.3 MHz, 2.3x4.0 cm2) using the rectangular radiator method. Array beamforming strategies were investigated to
deliver 30-min hyperthermia (<41 °C) to focal regions of prostate cancer, identified from MR images in representative
patient cases. Constraints on power densities, sonication durations and switching speeds imposed by ExAblate hardware
and software were incorporated in the models. T<41 °C was calculated in 14-19 cm3 for sonications with planar or
diverging beam patterns at 0.9-1.2 W/cm2, and in 3-10 cm3 for curvilinear (cylindrical) or multifocus beam patterns at
1.5-3.3 W/cm2, potentially useful for treating focal disease in a single posterior quadrant.
Preliminary experiments included beamformed sonications in tissue mimicking phantom material under MRI-based
temperature monitoring at 3T (GRE TE=7.0 ms, TR=15 ms, BW=10.5 kHz, FOV=15 cm, matrix 128x128, FA=40°).
MR-temperature rises of 2-6 °C were induced in a phantom with the ExAblate array, consistent with calculated values
and lower power settings (~0.86 W/cm2, 3 min.).
Conformable hyperthermia may be delivered by tailoring power deposition along the array length and angular expanse.
MRgERUS HIFU systems can be controlled for continuous hyperthermia in prostate to augment radiotherapy and drug
delivery. [FUS Foundation, NIH R01 122276, 111981].