Evaluating the Quality-of-Life Effect of Apical Spacing with Hyaluronic Acid Prior to Hypofractionated Prostate Radiation Therapy: A Secondary Analysis

Abstract

PurposeRecently, a randomized trial demonstrated that a hyaluronic acid (HA) spacer placed prior to prostate hypofractionated intensity-modulated radiation therapy improved rectal dosimetry and reduced acute grade 2+ gastrointestinal toxicity. However, 26.5% of patients receiving the spacer experienced a minimal clinically important decline (MCID) in bowel quality-of-life (QOL). The purpose of this study is to evaluate whether certain characteristics of the rectal spacer, as determined on post-implant imaging, were associated with change in bowel QOL at 3-months. Materials and MethodsThis is a secondary analysis of the 136 patients who received the HA spacer on the randomized trial. Post-implant spacer characteristics (i.e. prostate-rectum spacing at superior/mid-gland/inferior/apex planes, symmetry, prostate volume, spacer volume) were systematically analyzed from structure sets using custom software code. Characteristics demonstrating significant associations with rectal V30 on multivariate linear regression were identified. Linear regression models were used to analyze the associations of such characteristics with change (baseline to 3 months) in both bowel and urinary QOL. ResultsApical spacing (mean 9.7 (standard deviation 4.0)) was significantly smaller than spacing measurements at more superior planes. 95.6% of patients had a symmetric implant. Apical spacing (p < 0.001) and prostate volume (p = 0.01) were significantly associated with rectal V30 on multivariate analysis. However, only apical spacing (0.38/mm; p = 0.01) was associated with change in bowel QOL, even with adjustment of baseline bowel score (-0.33; p <0.01). Percentages of patients with bowel MCID were 14.8% for >= 10 mm versus 36.6% for <10 mm apical spacing (p = 0.01). Apical spacing was not associated with change in urinary QOL (-0.09; p = 0.72). when adjusted for baseline urinary QOL (-0.52; p < 0.01). ConclusionGreater apical spacing was associated with improved rectal dosimetry and smaller decline in bowel QOL at 3-months. Further prospective data are needed to fully understand the ramifications of increased apical spacing.