Injectable Spacer Preserves Bowels During Prostate Radiotherapy

Researchers at Texas Oncology (Irving, USA) reported the three-year follow-up results from a phase III trial in patients with low-intermediate risk prostate cancer who were injected with the SpaceOAR, an absorbable hydrogel rectal spacer that separates the rectum from the prostate during RT to potentially reduce the risk of adjacent organ-at-risk (OAR) injury. The researchers examined the cumulative incidence of toxicity and mean changes in quality of life (QoL) summary scores, based on previously established thresholds.

Three-year results showed that grade 1+ rectal toxicity incidence in patients with the SpaceOAR was just 2%, compared with 90% in controls. Incidence of grade 2+ rectal toxicity was 6% in the controls, with no cases of grade 2+ toxicity reported in those receiving SpaceOAR spacer. Grade 1+ urinary incontinence was lower in patients with the spacer (4%) than in controls (15%), but there was no difference in grade 2+ urinary effects between groups. The study was presented at the annual meeting of the American Society for Radiation Oncology (ASTRO), held during September 2016 in Boston (MA, USA).

“The distance between the prostate and rectum is typically 1-2 mm; a trans-perineal procedure can be used to place the hydrogel device between the prostate and the rectum, increasing the distance to approximately 1 cm, thus putting the rectum out of harm's way during radiotherapy,” said lead author and study presenter Daniel Hamstra, MD, PhD. “Rectal dosimetry was tremendously better after placement of the hydrogel spacer, and what this correlated with was a decrease in rectal toxicity. We saw significant and dramatic relative reductions of rectal dosimetry at all levels assessed.”

The SpaceOAR system, a product of Augmenix (Waltham, MA, USA), is a temporary hydrogel injected through the perineum, guided by transrectal ultrasound. The material flows into the space between the prostate and the rectum and expands within ten seconds, reducing rectum radiation during prostate RT. Shielding the rectum also permits dose escalation and hypo-fractionation, resulting in more prostate radiation, improved cancer kill rates, and fewer radiation treatment sessions. The hydrogel remains in place for three months and is then liquefied and absorbed, leaving nothing behind.

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