First Report of Transperineal Polyethylene Glycol Spacer Use to Curtail Rectal Radiation Dose Following Permanent 125I Prostate Brachytherapy

Abstract

To demonstrate the feasibility of transperineal polyethylene glycol (PEG) hydrogel insertion into anterior perirectal fat for reducing rectal radiation dose in patients with suboptimal rectal dosimetry following permanent 125I prostate brachytherapy. Patients with suboptimal day 30 post-implant rectal dosimetry following 125I prostate seed brachytherapy were approached for this study. This was defined according to updated American Brachytherapy Society concensus guidelines as rectal volume receiving prescribed dose >1.3 cubic centimeters (RV100>1.3cc). Four patients underwent a single transperineal injection of PEG hydrogel into the anterior perirectal fat under general anesthetic using transrectal ultrasound guidance. Prostate-rectum separation and rectal radiation dose before and after PEG hydrogel spacer insertion were measured. Toxicity due to spacer insertion was assessed at day 0-1 and 4-6 weeks using NCI Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v4.0). All patient experienced a clinically significant reduction in the volume of rectum receiving greater than or equal to the prescription dose (RV100) on the post-spacer post-implant dosimetry, compared with the pre-spacer post-implant dosimetry. Mean prostate-rectum separation that was achieved with the insertion of spacer was 14.7mm (± 3.8). The mean difference in separation from before to after spacer insertion was 11.9mm (± 4.9). This was associated with a reduction in mean rectal volume receiving prescribed dose or greater (RV100) from 3.2 (± 1.3) to 0.08 (± 0.05) cubic centimeters (cc).Tabled 1Pre-spacer Rectal V100 (cc)Post-spacer Rectal V100 (cc)Difference (cc)Patient 14.0404.04Patient 24.670.094.58Patient 32.010.121.88Patient 42.150.12.05Mean (n=4) ± SD3.22 ± 1.30.08 ± 0.13.14 ± 1.4 Open table in a new tab Two patients reported rectal fullness at day 0-1 following the procedure, and one patient had grade 1 perineal pain. There were no grade 2 or greater toxicities reported following insertion of the spacer. PEG hydrogel is safe and effective at reducing rectal radiation dose in select patients with suboptimal rectal dosimetry following prostate seed brachytherapy.