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Hyaluronic Acid Spacer May Reduce Rectal Dosimetry, GI Toxicity From Prostate Cancer Treatment


A randomized controlled trial found that the use of a rectal spacer may help mitigate the gastrointestinal (GI) toxicity associated with hypofractionated radiation therapy for prostate cancer.

Use of a hyaluronic acid rectal spacer during hypofractionated radiation therapy (HFRT) for prostate cancer may help improve rectal dosimetry and reduce acute grade 2 or higher gastrointestinal (GI) toxicities, according to findings from a randomized trial published in JAMA Oncology.1

HFRT, a more convenient and cost-effective alternative to conventionally fractionated radiation therapy (CFRT), has been increasingly used to treat prostate cancer in recent years. While many studies have shown HFRT to have similar efficacy to CFRT in low- and intermediate-risk prostate cancers, the study authors note that a recent meta-analysis found HFRT to be associated with a greater absolute risk of acute grade 2 or higher GI toxic effects vs CFRT.2 Rectal spacers that create distance between the prostate and rectum may reduce the risk of GI toxic effects related to HFRT by minimizing the amount of radiation exposure to the rectum.

The main end point in the study was radiation exposure, with researchers hypothesizing that more than 70% of patients in the rectal spacer group would experience at least a 25% reduction in the rectal volume receiving a radiation dose of 54 Gy (V54). The secondary end point was GI toxicity, with a hypothesis that those in the rectal spacer cohort would have noninferior acute grade 2 or higher GI toxic effects vs patients without a rectal spacer.

A total of 201 patients were included in the study, with 136 in the spacer group and 65 in the control group. Of the overall cohort, 63 patients received androgen deprivation therapy (ADT), the authors noted. Spacer injection was rated as easy or very easy by 92.7% of investigators in the study, and no procedural adverse events were reported. A total of 133 patients in the spacer group were evaluable for the primary end point, with 3 missing baseline scans.

In the rectal spacer cohort, 98.5% of patients (n = 131) experienced at least a 25% reduction in rectum V54. The mean reduction was 85%, and one of the 2 patients who did not achieve the main end point had received ADT.

Four patients in the spacer cohort (2.9%) and 9 in the control group (13.8%) experienced acute grade 2 or higher GI toxic effects. One patient in the spacer group and 3 in the control group who experienced GI toxic effects had received ADT.

Overall, the findings suggest that using a rectal spacer helps reduce radiation exposure to the rectum during treatment with HFRT, and the results are consistent with prior studies of patients receiving hyaluronic spacers before HFRT.

Although the study was limited by its short-term follow-up and by clinician investigators not being masked to the randomization group, the authors noted that the toxic effects were adjudicated by a committee masked to patient randomization.

“Given that HFRT has been associated with greater acute grade 2 or higher GI toxic effects than CFRT, rectal spacing may address a clinically important need for the large volume of patients receiving this effective and convenient treatment,” the authors wrote. They added that further prospective research is planned to follow up on the findings and characterize the effects of rectal spacing on long-term toxicities and patient quality of life.


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

2. Datta NR, Stutz E, Rogers S, Bodis S. Conventional versus hypofractionated radiation therapy for localized or locally advanced prostate cancer: a systematic review and meta-analysis along with therapeutic implications. Int J Radiat Oncol Biol Phys. 2017;99(3):573-589. doi:10.1016/j. ijrobp.2017.07.021

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