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SpaceOAR Hydrogel

SpaceOAR is an injectable polyethylene glycol (PEG) hydrogel placed between the prostate and the rectum before prostate radiation therapy. The hydrogel creates a physical spacer (approximately 1 cm) that separates the anterior rectal wall from the prostate, reducing the rectal dose of radiation and the incidence of radiation proctitis.

Composition & Timeline​

  • Biocompatible PEG hydrogel
  • Injected transperineally under ultrasound guidance before fiducial placement and planning
  • Absorbs progressively over 3–6 months
  • Completely cleared from the body within ~6 months

Why It's in the Biomaterials Reference​

Not a reconstructive urology biomaterial per se, but:

  • Reconstructive urologists increasingly encounter prior-SpaceOAR patients in the workup of post-radiation complications
  • Occasional misadventures (injection into the rectum, prostate, or vasculature) produce complications that come to the reconstructive clinic
  • The hydrogel is visible on imaging and may be mistaken for pathology by readers unfamiliar with it

Clinical Data​

Randomized data support reduction in acute and late rectal toxicity with SpaceOAR use in prostate radiation patients. It does not affect oncologic outcomes.

Imaging​

  • MRI: bright on T2-weighted sequences
  • CT: soft-tissue-density collection between prostate and rectum
  • Resolves progressively over 3–6 months — serial imaging shows shrinkage

See also: Radiation Tissue Effects, Rectovesical Fistula.