Feasibility and Short-Term Safety of Hydrogel Spacer before Treatment with Magnetic Resonance Imaging-Guided Transurethral Ultrasound Ablation for Prostate Cancer Treatment

<b><i>Purpose:</i></b> Magnetic resonance imaging (MRI)-guided transurethral ultrasound ablation (TULSA) is a minimally invasive method of ablating prostate cancer (PCa) using ultrasound energy under real-time temperature mapping provided by MRI. Posterior prostate tumors can be challenging to treat with adequate margins because of the proximity of the anterior rectal wall. We report our initial experience with rectal hydrogel spacer (spacer) placement in men undergoing TULSA for PCa treatment. <b><i>Materials and Methods:</i></b> A small cohort of men with spacers placed before TULSA were analyzed. Spacers were recommended in patients with posterior lesions near the rectal wall. Spacers were placed before TULSA with no other significant modifications during treatment day. Anatomical separation from the spacer was evaluated with <i>ad hoc</i> review of pre-/postspacer placement images. <b><i>Results:</i></b> Nine patients underwent TULSA with spacers in place, of which two patients had pre-existing spacers in preparation for radiation before switching to TULSA, and seven had intentional spacer placement because of posterior lesions. Spacers resulted in a median separation between the rectal wall and posterior prostate at the index lesion of 6 mm (interquartile range 3-8). All treatments were completed as planned with no additional artifact introduced because of the spacer. No postoperative complications were attributed to the presence of spacer during TULSA. <b><i>Conclusions:</i></b> We demonstrated that TULSA can be safely performed in patients with both polyethylene glycol-based and hyaluronic acid-based hydrogel rectal spacers. The presence of rectal spacer does not appear to impact thermoablation of targeted lesions and enables wider margins during posterior ablations.