Hyaluronic Acid Spacer for Hypofractionated Prostate Radiation Therapy A Randomized Clinical Trial

Importance Hypofractionated radiation therapy (RT) for prostate cancer has been associated with greater acute grade 2 gastrointestinal (GI) toxic effects compared with conventionally fractionated RT.Objective To evaluate whether a hyaluronic acid rectal spacer could (1) improve rectal dosimetry and (2) affect acute grade 2 or higher GI toxic effects for hypofractionated RT.Design, Setting, and ParticipantsThis randomized clinical trial was conducted from March 2020 to June 2021 among 12 centers within the US, Australia, and Spain, with a 6-month follow-up. Adult patients with biopsy-proven, T1 to T2 prostate cancer with a Gleason score 7 or less and prostate-specific antigen level of 20 ng/mL or less (to convert to mu g/L, multiply by 1) were blinded to the treatment arms. Of the 260 consented patients, 201 patients (77.3%) were randomized (2:1) to the presence or absence of the spacer. Patients were stratified by intended 4-month androgen deprivation therapy use and erectile quality.Main Outcomes and MeasuresFor the primary outcome, we hypothesized that more than 70% of patients in the spacer group would achieve a 25% or greater reduction in the rectal volume receiving 54 Gy (V54). For the secondary outcome, we hypothesized that the spacer group would have noninferior acute (within 3 months) grade 2 or higher GI toxic effects compared with the control group, with a margin of 10%.Results Of the 201 randomized patients, 8 (4.0%) were Asian, 26 (12.9%) Black, 42 (20.9%) Hispanic or Latino, and 153 (76.1%) White; the mean (SD) age for the spacer group was 68.6 (7.2) years and 68.4 (7.3) years for the control group. For the primary outcome, 131 of 133 (98.5%; 95% CI, 94.7%-99.8%) patients in the spacer group experienced a 25% or greater reduction in rectum V54, which was greater than the minimally acceptable 70% (P < .001). The mean (SD) reduction was 85.0% (20.9%). For the secondary outcome, 4 of 136 patients (2.9%) in the spacer group and 9 of 65 patients (13.8%) in the control group experienced acute grade 2 or higher GI toxic effects (difference, -10.9%; 95% 1-sided upper confidence limit, -3.5; P = .01).Conclusions and Relevance The trial results suggest that rectal spacing with hyaluronic acid improved rectal dosimetry and reduced acute grade 2 or higher GI toxic effects. Rectal spacing should potentially be considered for minimizing the risk of acute grade 2 or higher toxic effects for hypofractionated RT.