LBA 18 - Effectiveness and Safety of Pre-formed Radiopaque Hydrogel for Perirectal Spacing in Subjects with Low to Intermediate Risk Prostate Cancer Undergoing External Beam Radiotherapy: Preliminary Results of a Multicenter RCT (HYDROSPACE)
Presenter(s)
M. A. Fagundes1, M. J. Zelefsky2, S. A. Patel3, R. A. Hsi4, N. B. Desai5, L. Baum6, X. Shen7, T. McClintock8, J. Kaminetsky9, A. Berger10, T. P. Kole11, P. Chung12, A. Y. Jia13, A. Taggar14, L. H. Belkoff15, N. K. Taunk16, D. B. Fried17, T. Mendel18, M. R. Folkert19, D. A. Barron20, M. T. Corkum21, A. J. Chang22, A. Nanda23, D. Su24, P. Mehta Jr25, S. P. Collins26, D. Vannan27, P. O'Connor27, K. M. Haven27, and B. C. Baumann28,29; 1Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 2NYU Langone Health, New York, NY, 3Department of Radiation Oncology, Emory University, Atlanta, GA, 4University of Washington School of Medicine, Seattle, WA, 5University of Texas Southwestern Medical Center, Dallas, TX, 6Houston Metro Urology, Houston, TX, 7Department of Radiation Oncology, University of Kansas Medical Center, Kansas City, KS, 8Midtown Urology Associates, Austin, TX, 9Department of Urology, Perlmutter Cancer Center at New York University Grossman School of Medicine, New York, NY, 10Associated Urological Specialists, Chicago Ridge, IL, 11Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 12Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 13Department of Radiation Oncology, University Hospitals Cleveland Medical Center/ Seidman Cancer Center, Cleveland, OH, 14Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 15MidLantic Urology, Bala Cynwyd, PA, 16Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 17Gibbs Cancer Center & Research Institute, Spartanburg, SC, 18Rio Grande Radiation Oncology, El Paso, TX, 19Department of Radiation Oncology, University of Washington, Seattle, WA, 20Mercy Cancer Center Bon Secours Mercy Health, Elyria, OH, 21Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Ottawa, ON, Canada, 22Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 23Orlando Health Cancer Institute, Orlando, FL, 24Orange County Urology Associates, Laguna Hills, CA, 25UroPartners, Glenview, IL, 26University of South Florida, Tampa, FL, 27Boston Scientific, Marlborough, MA, 28Springfield Clinic, Springfield, IL, 29Hopewell Oncology, St. Louis, MO
Purpose/Objective(s):
Perirectal spacing is a guideline-supported strategy to help meet rectal dose constraints and reduce gastrointestinal AEs during prostate cancer radiotherapy (RT). Polyethylene glycol (PEG) hydrogel spacers are a common approach. The next-generation iodinated, pre-formed PEG hydrogel spacer studied in this clinical trial is radiopaque—visible on ultrasound, MRI, CT, and CBCT—and differs from current PEG hydrogels by being delivered as a pre-polymerized material, enabling flexibility to pause and resume injection with adjustment of the needle. The primary trial objective is safety and effectiveness evaluation in a large cohort of prostate cancer patients undergoing EBRT (including SBRT).Materials/Methods:
In this prospective, multi-center, multinational (US and Canada) randomized controlled trial (NCT06451614), the primary safety endpoint (PSE) is a non-inferiority evaluation of acute Grade 3+ AEs inclusive of all AEs listed on commercially available hydrogel perirectal spacer labels, arising within 90 days of index procedure. The primary effectiveness endpoint is a clinically relevant dose reduction defined as a 25% reduction in the rectal volume receiving 90% of prescribed radiation dose in subjects receiving the pre-formed radiopaque perirectal hydrogel spacer. Dosimetric comparisons were performed between pre- and post- spacer RT plans within each subject, with subjects serving as their own controls. A total of 230 subjects diagnosed with low to intermediate risk prostate cancer were randomized (1:1) to the intervention or the commercially available PEG-based hydrogel control group and treated with EBRT +/- short-term ADT.Results:
The pre-specified 3-month interim analysis results for 147 subjects (72 intervention, 75 control) are presented. Baseline characteristics were not significantly different between groups. All subjects had tumor stage T1-T2c, mainly stage T1c (83.3% intervention, 80.0% control). All had Gleason scores =7, most with pattern 3+4 disease (72.2% intervention, 68.0% control). The hydrogel was visible in the perirectal space in 100% of subjects after placement. For the PSE, non-inferiority was achieved for intervention compared with control (p=0.0017, boundary a level 0.0051). In the intervention arm, 92.4% (95% CI: 83.2, 97.5) of subjects had a 25% reduction in rectal V90%.Conclusion:
The iodinated, pre-formed PEG hydrogel spacer met the PSE for non-inferiority compared to commercially available PEG hydrogel spacers and demonstrated a reduction in rectal radiation dose. The study design, allowing for contemporary EBRT modalities across sites and involving paired pre- and post-spacer treatment plans, may further inform evaluation of spacing in modern RT practice.