Hydrogel Spacer Prospective Multicenter Randomized Controlled Pivotal Trial: Dosimetric  and Clinical Effects of Perirectal Spacer Application in XXXX Undergoing Prostate  Image Guided Intensity Modulated Radiation  Therapy.

@entity1 @entity137 @entity263 @entity548 @entity158
PURPOSE: Perirectal spacing, whereby biomaterials are placed between the prostate and rectum, shows promise in reducing rectal dose during @entity263 radiation therapy. A prospective multicenter randomized controlled pivotal trial was performed to assess outcomes following absorbable spacer (SpaceOAR system) implantation. METHODS AND MATERIALS: Overall, 222 @entity1 with clinical stage T1 or T2 @entity263 underwent computed tomography (CT) and magnetic resonance imaging (MRI) scans for treatment planning, followed with fiducial marker placement, and were randomized to receive spacer injection or no injection (control). @entity1 received postprocedure CT and MRI planning scans and underwent image guided intensity modulated radiation therapy (79.2  Gy in 1.8-Gy fractions). Spacer safety and impact on rectal irradiation, @entity137 , and quality of life were assessed throughout 15  months. RESULTS: Spacer application was rated as "easy" or "very easy" 98.7% of the time, with a 99% hydrogel placement success rate. Perirectal spaces were 12.6      3.9  mm and 1.6      2.0  mm in the spacer and control groups, respectively. There were no device-related adverse events, rectal perforations, serious @entity548 , or infections within either group. Pre-to postspacer plans had a significant reduction in mean rectal V70 (12.4% to 3.3%, P<.0001). Overall acute rectal adverse event rates were similar between groups, with fewer spacer @entity1 experiencing @entity158 (P=.02). A significant reduction in late (3-15  months) @entity137 severity in the spacer group was observed (P=.04), with a 2.0% and 7.0% late @entity137 incidence in the spacer and control groups, respectively. There was no late @entity137 greater than grade 1 in the spacer group. At 15  months 11.6% and 21.4% of spacer and control @entity1 , respectively, experienced 10-point declines in bowel quality of life. MRI scans at 12  months verified spacer absorption. CONCLUSIONS: Spacer application was well tolerated. Increased perirectal space reduced rectal irradiation, reduced @entity137 severity, and decreased rates of @entity1 experiencing declines in bowel quality of life. The spacer appears to be an effective tool, potentially enabling advanced prostate RT protocols.
