197 - Hydrogel Spacer Quality Assurance (QA) in a Multi-Center Randomized Control Trial of Neurovascular-Sparing SAbR for Localized Prostate Cancer (PCa)
Presenter(s)
K. Elfatairy1, P. S. Atluri1, R. T. Dess2, R. Hannan3, K. L. Stephans4, T. P. Robin5, A. N. Slade6, J. P. Christodouleas7, R. D. Tendulkar8, D. E. Spratt9, A. Garant3, W. C. Jackson2, D. X. Yang3, A. Goel10, A. C. Wong11, C. Gonzalez1, Y. Yan1, R. D. Timmerman3, M. Lee12, and N. B. Desai3; 1University of Texas Southwestern Medical Center, Dallas, TX, 2Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 3Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 4Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, 5Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, CO, 6Department of Radiation Oncology, Stony Brook University Hospital, Stony Brook, NY, 7Elekta, Stockholm, Sweden, 8Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, 9Department of Radiation Oncology, University Hospitals Cleveland Medical Center/ Seidman Cancer Center, Cleveland, OH, 10University of Pennsylvania, Philadelphia, PA, 11University of California San Francisco, Department of Radiation Oncology, San Francisco, CA, 12Department of Health Data Science & Biostatistics, University of Texas Southwestern Medical Center, Dallas, TX
Purpose/Objective(s):
To assess how hydrogel spacer quality affects rectal dosimetry, acute toxicity and quality of life (QoL) in a clinical trial of PCa SAbR.Materials/Methods:
This is a post hoc analysis of a fully accrued patient-blinded phase II multicenter randomized control trial, which evaluated mitigation of sexual function decline by Expanded Prostate Cancer Index Composite (EPIC) instrument using MR-based neurovascular-sparing SAbR (40-45Gy/5fx randomly assigned neurovascular de-escalation to 30Gy). Hydrogel spacer placement was required. Spacer QA was performed by a GU radiologist on treatment planning T2-weighted MRI images according to published semiquantitative score (SQS) for separation of rectum/prostate (increasing score 0-2 reflecting more consistent spacing) and rectal wall infiltration (RWI) score (0 no infiltration, 1-3 increasing infiltration). Univariate correlations to EPIC QoL and physician-reported toxicity at 3 months and to rectal dosimetry were made using Chi-square test for categorical variables and by t-test or ANOVA for continuous variables, and linear regression was used for multivariable analysis for continuous outcome variables of interest. Significance level was set at p=0.05.Results:
Of 120 men randomized, 103 (86%) had available post-spacer MR imaging and 3 month toxicity/QoL data at time of analysis. There were no acute grade >=3 toxicities observed in the overall study or this cohort, and thus analyses were focused on dosimetry, grade 1-2 toxicity and QoL scores. SQS scores were 0 (10, 10%), 1 (70, 68%), and 2 (23, 22%). For RWI scores, most had no infiltration (76, 74%) with a minority having increasing degrees of infiltration: score 1 (17, 16%), score 2 (6, 6%), or score 3 (4, 4%). Distribution of SQS and RWI did not differ significantly between study arms but were more favorable in those prescribed to 45Gy vs 40Gy (SQS 0/1/2: 11%/77%/12% vs 8%/57%/35%, p=0.02; RWI 0/1/2/3: 63%/23%/9%/5% vs 87%/9%/2%/2%, p=0.06). Increasing SQS score was significantly correlated with lower rectum Dmax (SQS score, mean Dmax [SD]: 0, 44.6Gy [3.1]; 1, 39.8 Gy [5.0]; 2, 37.5 Gy [7.2], p<0.01), which held significant after adjusting for study arm and prescribed dose (p<0.01). In contrast, no statistically significant difference was noted by SQS for physician-reported GI toxicity at 3 months (p=0.18) or for 3-month bowel EPIC-26 score change from baseline (p=0.96).RWI was not associated with rectal dose (p=0.89), 3 month physician-reported GI toxicity (p=0.23), or EPIC-26 bowel score change from baseline (p=0.72).Conclusion:
Quantitative hydrogel spacer trial QA demonstrated that while higher SQS scores correlated to lower max rectal dose, there was no apparent impact of SQS score or RWI on acute rectal toxicity or patient-reported QoL. Longer term impact will be determined in follow up analyses.