Quantitative evaluation of recto-prostatic distance before and after SpaceOAR hydrogel placement.

[AIM] Radiation is the standard therapy for prostate cancer. However, it may cause damage to the surrounding organs, including the rectum. SpaceOAR hydrogel is a Food and Drug Administration (FDA)-approved spacer which increases the distance between the rectum and prostate, reducing rectal radiation exposure. A 7.5 mm distance is considered desirable for radiation toxicity purposes. This study aims to quantify the increased recto-prostatic distance after SpaceOAR hydrogel placement.

[MATERIALS AND METHODS] A total of 118 consecutive patients who underwent magnetic resonance imaging (MRI) prior to and after SpaceOAR hydrogel placement were included. The distance between the prostate and rectum distance (PRD) was measured in nine different locations, including one centimetre superior to the apex, inferior to the base, and at the level of mid-gland on sagittal views, and one centimetre to the left, right, and midline of the prostate on axial views. The measured data were recorded in Microsoft Excel and compared before and after SpaceOAR hydrogel placement.

[RESULTS] The average PRD was significantly different before and after SpaceOAR hydrogel placement at all locations (P < 0.001). The mean PRD increased throughout the entire prostate (ranging from 8 ± 3 mm at base to 12 ± 14 mm at the apex). Although the averages were significantly different, up to 57% of patients did not achieve a PRD of 7.5 mm after SpaceOAR hydrogel placement.

[CONCLUSION] Although SpaceOAR hydrogel increases the mean PRD, the distribution of SpaceOAR hydrogel between the rectum and prostate may not be uniform, which may leave some portions of the rectum at increased risk for radiation toxicity.