(UroToday.com) The 2023 AUA annual meeting included a local prostate cancer radiotherapy session, featuring a presentation by Dr. Jonathan Kam discussing a real-world assessment of MRI predictors of rectal complications following transperineal SpaceOAR® hydrogel insertion. By way of background, Dr. Kam notes that a hydrogel spacer is placed between the prostate and rectum, aiming to reduce radiation dose to the rectum and rectal toxicity. This typically remains stable for 3 months and is reabsorbed by 6 months post-placement. The 2015 SpaceOAR® US PIVOTAL trial was a randomized clinical trial of 222 men randomized 2:1 to spacer versus control, with key inclusion criteria of T1/T2 prostate cancer and prostate volume <80 cc.1
In this trial, acute toxicity (<6 months) showed no difference between the two groups: >= G1 34.2% vs 31.5% and >=G2 rectal toxicity 4.1% vs 4.2%. This trial suggests that SpaceOAR® is very safe, however, 51% of patients had asymmetrical placement (but still resulted in rectal dose reduction), and 6% of patients had rectal wall infiltration (but with no correlation with adverse events). As such, the SpaceOAR® hydrogel product information does not recommend post-insertion MRI imaging to confirm deployment position. However, post-market surveillance, specifically data from the MAUDE database, suggests that significant complications are much more common than suggested by the original SpaceOAR® PIVOTAL trial.1 Additional case series have also suggested higher real world complication rates:
In the current study, Dr. Kam and colleagues aimed to assess ‘real-world’ 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.
This study was a retrospective audit of all men who underwent transperineal SpaceOAR® hydrogel insertion at 2 centers (Nepean Public Hospital and Nepean Private Hospital) from 2018 to 2021 prior to radiotherapy for prostate cancer. This audit included an assessment of rectal toxicity (electronic medical records) and post-SpaceOAR® MRI for symmetry and rectal wall infiltration according to the PIVOTAL trial protocol. Baseline demographics, procedural details, and post-operative outcomes were collected. Rectal complications were assessed and correlated to MRI findings. SpaceOAR® symmetry was assessed as follows:2
Additionally, the rectal wall invasion scoring method was as follows:2
In total, 141 patients were identified of which 87 had post-insertion MRIs performed. The median age was 72 years (range: 51–84 years) and median PSA was 9.9 ng/mL (range: 3.1–23 ng/mL). Proportions of prostate cancer grade group (GG) were GG2 48%, GG3 16%, GG4 23%, and GG5 13%. Four patients (3%) had significant rectal complications, including two patients with a grade 2 rectal ulcer, one patient developed a rectourethral fistula, and one patient had severe constipation with radiotherapy delayed by 1 month to allow for colonoscopy to exclude a rectal ulcer. There appeared to be no association with the symmetry of SpaceOAR placement and the development of significant rectal complications. The symmetry data in the current study was comparable to the PIVOTAL trial data:
Overall, there were 36 (41%) cases that had rectal wall infiltration on the post-SpaceOAR insertion MRI, which included 20 (23%) grade 1, nine (11%) grade 2, and seven (8%) grade 3 events. GI symptoms are not a good predictor of rectal wall infiltration, with only two of the seven cases of grade 3 rectal wall infiltration having GI symptoms. Among the seven patients with grade 3 rectal wall invasion, two had significant rectal toxicity, and two were symptomatic (one patients with rectal ulcer; one patient with severe constipation). Additionally, grade 3 rectal wall invasion was associated with higher risk of rectal toxicity: 29% vs 2.5% (p = 0.03).
Dr. Kam concluded his presentation discussing a real-world assessment of MRI predictors of rectal complications following transperineal SpaceOAR hydrogel insertion with the following take-home messages:
- This real-world data suggests SpaceOAR® hydrogel insertion results in a much higher rectal wall infiltration rate than suggested by the PIVOTAL trial (6% in PIVOTAL trial vs. 41% in this cohort) and there is increasing evidence of complications with SpaceOAR® in the literature and this series
- Grade 3 rectal wall infiltration was associated with a significant risk in significant rectal complications
- Given that rectal wall infiltration could not be predicted by GI symptoms, SpaceOAR® insertion should be followed by an MRI to ensure there is no significant rectal wall infiltration; this should be routine, which is contrary to the product information that suggests post-insertion is not required
- 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
Presented by: Jonathan Kam, Nepean Hospital, Sydney, Australia
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2023 American Urological Association (AUA) Annual Meeting, Chicago, IL, April 27 – May 1, 2023
References:
- Mariados N, Sylvester J, Shah D, et al. Hydrogel spacer prospective multicenter randomized controlled PIVOTAL Trial: Dosimetric and clinical effects of perirectal spacer application in men undergoing prostate imaging guided intensity modulated radiation therapy. Int J Radiat Oncol Biol Phys. 2015 Aug 1;92(5):971-977.
- Fischer-Valuck BW, Chundury A, Gay H, et al. Hydrogel spacer distribution within the perirectal space in patients undergoing radiotherapy for prostate cancer: impact of spacer symmetry on rectal dose reduction and the clinical consequences of hydrogel infiltration into the rectal wall. Pract Radiat Oncol. 2017;7:195-202