First report of transperineal polyethylene glycol hydrogel spacer use to curtail rectal radiation dose after permanent iodine-125 prostate brachytherapy.

PURPOSE 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 after permanent iodine-125 prostate brachytherapy. METHODS AND MATERIALS Five patients with suboptimal rectal dosimetry after iodine-125 seed brachytherapy implant 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 because of spacer insertion was assessed at Days 0-1 and 4-6 weeks using National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0. RESULTS All patients experienced a clinically significant reduction in the volume of rectum receiving greater than or equal to the prescription dose (RV100) on the postspacer postimplant dosimetry, compared with the prespacer postimplant dosimetry. Mean prostate-rectum separation that was achieved with the insertion of the spacer was 15.1 mm (±3.4). The mean difference in separation from before to after spacer insertion was 12.5 mm (±4.5). This was associated with a reduction in mean RV100 from 3.04 (±1.2) to 0.06 (±0.1) cc. Toxicities were limited to Grade 1 (National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0) perineal pain and rectal discomfort (3/5 patients). There were no Grade 2 or greater toxicities reported after insertion of the spacer. CONCLUSIONS PEG hydrogel is safe and effective at reducing rectal radiation dose in select patients with suboptimal rectal dosimetry after prostate seed brachytherapy.