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Clinical summary

Rectal Hydrogel Spacer Improves Late Gastrointestinal Toxicity Compared to Rectal Balloon Immobilization After Proton Beam Radiotherapy for Localized Prostate Cancer: A Retrospective Observational Study

By: Dinh TT, Lee HJ, Macomber MW, et al.

From 2013 to 2018, 267 patients with localized, clinical stage T1–4 prostate adenocarcinoma were treated at a single institution using conventionally fractionated, dose-escalated PBT.¹ 192 patients were treated with rectal balloon immobilization and 75 were treated with rectal spacer. Patient-reported GI toxicity was prospectively collected while the incidence of rectal bleeding was retrospectively reviewed from patient records.¹

Grade 2+ GI toxicity or rectal bleeding across reported trials

Grade 2+ GI Toxicity or Rectal Bleeding bar graph.

“Use of rectal hydrogel spacer for prostate proton beam therapy is associated with significantly lower incidence of clinically relevant, late rectal bleeding and lower decrement in long-term, patient-reported bowel QOL compared with rectal balloon immobilization. Our results suggest that hydrogel spacer may improve rectal sparing compared to rectal balloon immobilization during proton beam therapy for prostate cancer.”

Limitations of this report include:

  • Study was retrospective in nature.
  • The SpaceOAR™ Hydrogel pivotal study did not use PBT so the results may not be comparable.
  • This study was not designed or powered to make definitive claims about the benefits of a spacer.
  • These results may not be achieved with other PBT protocols.
  • A limitation of these data is the high drop-out rate in reporting with followup, though the rates are roughly similar between cohorts. A patient-level analysis of EPIC scores was not possible due to the limited number of patients with scores at all time points.
  • Incidences of RB were retrospectively graded, and thus subject to availability and heterogeneity of records.
  • High-risk patients comprised a higher proportion in the rectal balloon immobilization group, in large part because patients with ECE, SVI, or local invasion were precluded from receiving hydrogel spacer.

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  1. Dinh TKT, Lee Jr HJ, Macomber MW, et al. Rectal hydrogel spacer improves late gastrointestinal toxicity compared to rectal balloon immobilization after proton beam radiation therapy for localized prostate cancer: a retrospective observational study. Int J Radiat Oncol Biol Phys. 2020 Nov 1;108(3):635–43.

PBT was not the method used in the SpaceOAR™ Hydrogel single-blind Phase III trial performed to evaluate dosimetric and clinical effects of SpaceOAR Hydrogel. IG-IMRT delivered at 79.2 Gy in 1.8-Gy fractions was the method used.

Results from case studies are not necessarily predictive of results in other cases. Results in other cases may vary.

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