Main Session
Sep
29
PQA 06 - Genitourinary Cancer, Gynecological Cancer, and Health Care Access and Engagement
3255 - Longitudinal Characterization of Rectal Spacing Achieved by Two Commercial Rectal Spacer Products
Presenter(s)
Ryan Davis, MD - City of Hope National Medical Center, Duarte, CA
R. S. Davis1, C. Tapia2, S. Maroongroge1, J. Y. C. Wong1, R. Li1, S. V. Dandapani1, P. Lee3, S. M. Glaser1, J. Weng4, W. Yip5, B. Yuh5, K. Wittig6, and C. J. Ladbury1; 1Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, 2City of Hope National Medical Center, Irvine, CA, 3City of Hope Radiation Oncology, Irvine, CA, 4City of Hope Orange County, Irvine, CA, 5Department of Surgery, City of Hope National Medical Center, Duarte, CA, 6City of Hope National Medical Center, Lancaster, CA
Purpose/Objective(s):
Rectal spacers are designed to reduce rectal dose during radiotherapy for prostate cancer, with the intention of reduced toxicity. The two most commonly used commercially available rectal spacers are made of polyethylene glycol polymer and hyaluronic acid. Given that hyaluronic acid does not polymerize during placement, this may allow for greater sculpting flexibility. We hypothesized that a greater rectoprostatic separation could be achieved with hyaluronic acid compared to polyethylene glycol.Materials/Methods:
We performed a retrospective, single-institution cohort study. Men with prostate cancer who underwent spacer placement prior to definitive radiotherapy were identified and a total of 80 consecutive patients were selected (40 hyaluronic acid, 40 polyethylene glycol). These patients were treated from March 2023 through August 2025. Rectoprostatic separation (cm) was measured at five anatomic locations (base, midgland left/middle/right, and apex) on the simulation CT as well as the CBCT at the time of the first and last fraction of treatment. Separation was analyzed at each anatomic site using linear mixed-effects models with patient-level random intercepts, adjusting for prostate volume, spacer product, time point, and product-by-time interaction.Results:
At the time of CT simulation, polyethylene glycol demonstrated greater separation than hyaluronic acid at the base, (0.199 cm, 95% CI 0.055-0.343; p=0.007), midgland middle (0.202 cm, 95% CI 0.077-0.327; p=0.002), and midgland right (0.151 cm, 95% CI 0.029-0.273; p=0.016) with no differences observed at the midgland left (0.075 cm, 95% CI -0.056-0.207; p=0.263) or apex (-0.014 cm, 95% CI -0.303-0.274; p=0.923). A product-by-time interaction was observed at the first fraction with polyethylene glycol demonstrating an increased gap relative to hyaluronic acid at the base (0.145 cm, 95% CI 0.038-0.252; p=0.008), midgland left (0.152 cm, 95% CI 0.049-0.255; p=0.004) and midgland middle (0.103, 95% CI 0.012-0.195; p=0.027). At the last fraction, polyethylene glycol demonstrated an increased gap at the midgland middle (0.107 cm, 95% CI 0.015-0.199; p=0.022). Increasing prostate size was correlated with decreased rectoprostatic separation at the midgland right (-0.002 cm per cc, 95% CI -0.004-0.000; p=0.023)Conclusion:
In this retrospective analysis which incorporated longitudinal imaging throughout treatment, polyethylene glycol produced a statistically significantly (though likely not clinically significant) increased separation in rectoprostatic separation than hyaluronic acid at several anatomic sites at CT simulation and throughout treatment.