A rectal spacer with hyaluronic acid can reduce the risk for gastrointestinal toxicity from hypofractionated prostate cancer radiation therapy, recent study findings suggest.

Hypofractionated radiation therapy for prostate cancer is more convenient and cost effective than conventionally fractionated radiation therapy, but it has been associated with greater acute grade 2 gastrointestinal toxic effects. Rectal spacers create distance between the prostate and rectum, thereby reducing the rectal volume receiving a high radiation dose.

A team led by Martin King, MD, PhD, of Brigham and Women’s Hospital in Boston, Massachusetts, conducted a clinical trial from March 2020 to June 2021 involving 12 centers in the United States, Australia, and Spain. The trial had a 6-month follow-up period. They randomly assigned 201 patients to receive a hyaluronic acid spacer plus fiducial markers (136 patients) or fiducial markers only (control group, 65 patients) followed by hypofractionated radiation therapy.

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The primary outcome was a 25% or greater reduction in the rectal volume receiving 54 Gy (V54) of radiation. The investigators hypothesized that more than 70% of patients in the spacer group would achieve this primary outcome.

Results showed that 131 (98.5%) of 133 patients in the spacer group (the investigators excluded 3 patients from the primary efficacy analysis) experienced the primary outcome, Dr King and colleagues reported in JAMA Oncology. The mean reduction in rectum V54 was 85%. In addition, 2.9% of the spacer recipients experienced grade 2 or higher gastrointestinal toxic effects compared with 13.8% of the control group, a significant 10.9% difference.

“The trial results suggest that hyaluronic acid rectal spacer should be considered for patients who are receiving hypofractionated radiation therapy,” the investigators concluded.

The study population included men with biopsy-proven T1 to T2 prostate cancer with a Gleason score of 7 or less and PSA level of 20 ng/mL or less. The median age of patients in the spacer and control groups was 68.6 years and 68.4 years, respectively. The majority of patients (76.1%) were White.


Mariados NF, Orio PF III, Schiffman Z, et al. Hyaluronic acid spacer for hypofractionated prostate radiation therapy. A randomized clinical trial. JAMA Oncol. Published online February 9, 2023. doi:10.1001/jamaoncol.2022.7592