Acoustic Access to the Prostate for Extracorporeal Ultrasound Ablation

Abstract

This study aimed to measure acoustic access to the prostate for extracorporeal ultrasound ablation. Both transabdominal and transperineal approaches were considered. The objective was to measure the size and shape of the aperture available for unobstructed targeting of the prostate. CT images of 17 randomly selected men >56 years of age were used to create 3D reconstructions of the lower abdomen and pelvis. Rays were traced from target locations in the prostate toward the perineum and the abdomen. The maximum CT density encountered along each path was recorded; those paths that traversed structures with CT density exceeding a soft tissue threshold were considered to be blocked by bone. Unblocked rays comprised the accessible aperture. The aperture through the perineum was found to be a triangular-shaped region bounded by the lower bones of the pelvis varying significantly in size between subjects. The free aperture through the abdomen was wedge shaped limited by the pubis and also with great subject-to-subject variability. Average unblocked fractions of an f=1 transducer to target base, middle, and apex of the prostate along the urethra from the perineum were 77.0%, 94.4%, and 99.6%, respectively. Averages targeting from the abdomen were 86.1%, 52.3%, and 11.0%. Acoustic access to the prostate for therapy through the perineum was judged to be feasible. Access from the abdomen was judged to be sufficient for the base of the prostate, but likely inadequate for the middle and apex.

Histotripsy of the Prostate Using a Commercial System in a Canine Model

“…Previous work reconstructing human pelvic bone anatomy revealed this to be a much more efficient way to deliver acoustic energy to the prostate than the suprapubic approach. 21 In this configuration, the structure behind the targeted prostate volume will be the trigone and lumen of the bladder and the rectum will not be within the acoustic path.…”

Histotripsy Fractionation of Prostate Tissue: Local Effects and Systemic Response in a Canine Model

“…Firstly, differences in pelvic anatomy (longer path length and intervening bones) may limit use of an abdominal approach for acoustic targeting the prostate. Analysis of human cross-sectional images and reconstructions suggests a perineal approach provides sufficient acoustic access to the prostate 19. Additionally, transrectal access may become practical when engineering advances lead to development of small transducer elements sufficiently powerful to initiate cavitation.…”

Development and translation of histotripsy

“…Three dimensional reconstructions of the pelvic bony anatomy and prostate were used to back project from the prostate to the therapy transducer located in either a perineal or suprapubic location. The perineal approach was superior, allowing an average unblocked transducer surface area of 77.0%, 94.4%, and 99.6% when targeting the base, middle, and apex of the prostate [24]. A transrectal approach is used by commercial prostate HIFU systems and would also simplify targeting and energy deliver with histotripsy.…”