Real-World Data on Barrigel and SpaceOAR Rectal Spacers in Prostate Cancer Radiation Therapy: A Comparative Analysis

: Hydrogel rectal spacers are in widespread and routine clinical use for prostate cancer radiation therapy. Theses spacers separate the prostate from the rectum, thereby reducing the radiation dose to the rectum. Two major hydrogels are in use, SpaceOAR and Barrigel, yet there are no real-world data comparing these two. This study aims to compare these gels with respect to quality of insertion and dosimetric outcomes.

A multicenter retrospective analysis was performed on all men with prostate cancer undergoing radiation therapy from 2017 to 2023. Demographic, radiation therapy, and magnetic resonance imaging details were imported for analysis. Each multiparametric magnetic resonance imaging was scored on rectal spacing placement by 2 independent observers.

Eight hundred twenty-two patients were included for dosimetric and 605 for quality of insertion analysis. The median SpaceOAR volume (13.80 cc) was larger than the median Barrigel volume (5.10 cc) (P < .01). SpaceOAR was more likely to achieve a higher Spacer Quality Score (SQS) compared to Barrigel (5-fraction odds ratio [OR], 6.25; >5 fractions OR, 2.16; P < .01 for both respectively). SpaceOAR achieved lower irradiated rectal volumes for 20 fractions, at v60, v46, v38, and v30 (P < .01 for all) and 5 fractions, v30 (P = .04), v20 (P = .01). After accounting for spacer volume, Barrigel achieved better rectal dosimetric outcomes for 20 fraction patients compared to SpaceOAR for volumes between 6 and 13 cc, v57 (P = .01), v54 (P = .01). Higher SQS correlated with improved dosimetric outcomes (P < .05), whereas no similar monotonic trend was observed with the Fischer-Valuck (FV) score across evaluated dose levels, including v36 (P = .10), v32 (P = .26), and v30 (P = .45). Incidence of rectal wall infiltration among SpaceOAR patients was 7/287 (2.44%) compared to none for Barrigel.

Real-world data show that SpaceOAR achieves better dosimetry than Barrigel likely due to larger insertion volumes. At similar insertion volumes, Barrigel achieves lower irradiated rectal volumes compared to SpaceOAR. Dosimetric outcomes are more likely impacted by volume rather than symmetry of insertion. The SQS scoring method may have better utility than the FV scoring method for assessing dosimetric outcomes. Our data also indicate that Barrigel has a lower incidence of rectal wall infiltration compared with SpaceOAR.