Rectal Dosimetry of Different Rectal Displacement Devices for Prostate External Beam Radiation Therapy: A Multi-Institutional Retrospective Cohort Study

Purpose Multiple rectal displacement device (RDD) technologies are in use or under development for the reduction of rectal toxicity in prostate cancer. In this multi-institutional retrospective cohort study, we compare the rectal dose-sparing capabilities of 2 types of RDD: polyethylene glycol (PEG) gel and inflatable balloon (IB). Materials and Methods Dose-volume parameters of D0.1cc, D1cc, and D2cc to the rectum were used as endpoints for late rectal toxicity. All dosimetry values were converted to equivalent dose in 2 Gy fractions with α/β of 3 to better compare patients receiving differing treatment fractionation schedules. Results Dosimetric data were analyzed for 283 patients. Of those patients, 99 received a PEG implant, 92 received an IB implant, and 92 received neither implant. Both RDD types (PEG and IB) reduced the dose to the rectum for all dose-volume parameters (D0.1cc, D1cc, D2cc) compared to the control cohort. The IB implant yielded a dose reduction of 10% compared to control patients for D0.1cc, a reduction of 17% for D1cc, and a reduction of 21% for D2cc. The PEG implant resulted in a dose reduction of 2% compared to control patients for D0.1cc, a reduction of 7% for D1cc, and a reduction of 11% for D2cc. Compared to the PEG implant, the IB implant reduced the dose by 8% for D0.1cc, by 11% for D1cc, and by 12% for D2cc. Conclusions The use of both PEG and IB spacers significantly reduces dose to the rectum. The IB spacer provides a greater reduction in dose than the PEG spacer.