Histotripsy of the prostate using a commercial system in a canine model

Histotripsy is a focused ultrasound technology that uses controlled acoustic cavitation to homogenize targeted tissue. We assessed local and systemic effects after histotripsy treatment with the Vortx RX® system in a canine model. The system was not approved for human use at the time of the study.

Histotripsy was applied in 10 intact male dogs. The therapy transducer (36 elements, 700 kHz and 11 cm focal distance) delivered acoustic bursts (3 cycles and 500 Hz pulse repetition frequency) transabdominally to the prostate for 60 minutes. Tissue and systemic response were assessed by transrectal ultrasound, cystoscopy and interval evaluation of blood and urine parameters. Prostates were harvested on postoperative day 2 in 2 dogs and on postoperative day 28 in 8.

A treatment cavity was apparent in each prostate on transrectal ultrasound and cystoscopy. Mean prostate volume decreased 36% (range 19% to 53%) by postoperative day 28. Although clinical symptoms were not produced, notable pathological findings at necropsy consisted of rectal wall muscle degeneration in 2 animals and concern for a potential histotripsy effect and 1 cm diameter areas of fibrosis in the abdominal rectus muscle in 2 animals suggestive of thermal injury along the acoustic propagation path to the prostate.

Extracorporeal application of histotripsy produced prostate debulking in all dogs. Pathological findings of collateral injury are of concern since this may represent suboptimal confinement of cavitation or heating of overlying tissue. Further study is under way to quantify the prefocal thermal fields to eliminate these effects before human application.