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

PURPOSE - Perirectal spacing, whereby biomaterials are placed between the prostate and rectum, shows promise in reducing rectal dose during prostate cancer radiation therapy. A prospective multicenter randomized controlled pivotal trial was performed to assess outcomes following absorbable spacer (SpaceOAR system) implantation.

METHODS - Overall, 222 patients with clinical stage T1 or T2 prostate cancer 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). Patients 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, toxicity, 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 bleeding, 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 patients experiencing rectal pain (P=.02). A significant reduction in late (3-15 months) rectal toxicity severity in the spacer group was observed (P=.04), with a 2.0% and 7.0% late rectal toxicity incidence in the spacer and control groups, respectively. There was no late rectal toxicity greater than grade 1 in the spacer group. At 15 months 11.6% and 21.4% of spacer and control patients, 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 rectal toxicity severity, and decreased rates of patients experiencing declines in bowel quality of life. The spacer appears to be an effective tool, potentially enabling advanced prostate RT protocols.

Int J Radiat Oncol Biol Phys. 2015 Aug 1;92(5):971-7. doi: 10.1016/j.ijrobp.2015.04.030. Epub 2015 Apr 23.

Mariados N1, Sylvester J2, Shah D3, Karsh L4, Hudes R5, Beyer D6, Kurtzman S7, Bogart J8, Hsi RA9, Kos M10, Ellis R11, Logsdon M12, Zimberg S13, Forsythe K14, Zhang H15, Soffen E16, Francke P17, Mantz C18, Rossi P19, DeWeese T20, Hamstra DA21, Bosch W22, Gay H22, Michalski J22.

1 Associated Medical Professionals of New York, Syracuse, New York.
2 21st Century Oncology, East Bradenton, Florida.
3 Western New York Urology Associates, Cancer Care of WNY, Cheektowaga, New York.
4 The Urology Center of Colorado, Denver, Colorado.
5 Chesapeake Urology Research Associates, The Prostate Center, Owings Mills, Maryland.
6 Arizona Oncology Services Foundation, Phoenix, Arizona.
7 Urological Surgeons of Northern California, Campbell, California.
8 The Research Foundation of State University of New York, SUNY Upstate Medical University, Syracuse, New York.
9 Peninsula Cancer Center, Poulsbo, Washington.
10 Urology Nevada, Reno, Nevada.
11 University Hospitals Case Medical Center, Cleveland, Ohio.
12 Sutter Health Sacramento Sierra Region, Sutter Institute for Medical Research, Sacramento, California.
13 Advanced Radiation Centers of New York, Lake Success, New York.
14 Oregon Urology Institute, Springfield, Oregon.
15 University of Rochester, Rochester, New York.
16 CentraState Medical Center, Freehold, New Jersey.
17 Carolina Regional Cancer Center, 21st Century Oncology, Myrtle Beach, South Carolina.
18 21st Century Oncology, Fort Meyers, Florida.
19 Emory University, Atlanta, Georgia.
20 The Johns Hopkins University, Baltimore, Maryland.
21 Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
22 Washington University School of Medicine, St. Louis, Missouri.

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