SpaceOAR hydrogel product information suggests that deployment does not need to be confirmed with post-insertion MRI imaging. Post-market surveillance suggests significant complications are much more common than suggested by the original SpaceOAR PIVOTAL trial. We aimed to assess the symmetry of deployment and rates of rectal wall infiltration during transperineal placement of prostate-rectum hydrogel spacers (SpaceOAR™) for patients with prostate cancer and their association with significant rectal toxicity.

A retrospective audit of all men who underwent transperineal SpaceOAR hydrogel insertion at 2 centres (Nepean Public Hospital and Nepean Private Hospital) from 1 January 2017 to 30 June 2021 prior to radiotherapy for prostate cancer was undertaken. Baseline demographics, procedural details and post-operative outcomes were collected. Post-insertion MRIs were assessed for symmetry and rectal wall infiltration (RWI) according to the PIVOTAL trial protocol. Rectal complications were assessed and correlated to MRI findings.

In total 141 patients were identified of which 87 had post-insertion MRIs performed. The median age was 72 years (range: 51 – 84 years), median PSA was 8ng/mL (range: 3.1 – 23ng/mL). Proportions of prostate cancer grade group (GG) were GG2 48%; GG3 16%; GG4 23% and GG5 13%. 36 (41%) cases had rectal wall infiltration on the post-SpaceOAR insertion MRI. 20 (23%) were grade 1, 9 (10%) grade 2 and 7 (8%) were grade 3. Three patients had significant rectal complications, 2 patients had a grade 2 rectal ulcer, and 1 patient developed a rectourethral fistula. All 3 cases had significant grade 3 RWI on MRI, suggesting that grade 3 RWI is a significant risk factor for rectal complications post SpaceOAR insertion. GI symptoms are not a good predictor of RWI, with only 2 of the 7 cases of grade 3 RWI having GI symptoms. For the 2 patients with rectal ulcers- 1 patient had their radiotherapy delayed by 3 months and the other patient proceeded to radical prostatectomy. 1 patient had significant infiltration of SpaceOAR into the prostate. There appeared to be no association with the symmetry of SpaceOAR placement and the development of significant rectal complications.

Our real-world data suggests SpaceOAR hydrogel insertion results in a much higher RWI rate than suggested by the PIVOTAL trial (6% in PIVOTAL trial vs. 41% in our cohort). Grade 3 RWI was associated with a significant risk in significant rectal complications. Given that RWI could not be predicted by GI symptoms, SpaceOAR insertion should be followed by an MRI to ensure there is no significant rectal wall infiltration. In cases with significant rectal wall infiltration delay of treatment and referral for colorectal assessment for the presence of rectal ulceration should be considered to prevent serious rectal complications.