LBA 17 - Primary Endpoint Analysis of a Multi-Center Phase II Randomized Control Trial of Neurovascular-Sparing SAbR in Localized Prostate Cancer (Late Breaking Abstract)

09:15am - 09:25am ET

Room 253

Presenter(s)

Neil Desai, MD - University of Texas Southwestern Medical Center, Dallas, TX

N. B. Desai¹, K. Pithadia², R. T. Dess³, R. Hannan², K. L. Stephans⁴, T. P. Robin⁵, A. N. Slade⁶, J. P. Christodouleas⁷, R. D. Tendulkar⁸, D. E. Spratt⁹, A. Garant², W. C. Jackson³, D. X. Yang², A. Goel¹⁰, A. C. Wong¹¹, C. Gonzalez², S. Neufeld¹, C. Ahn¹², Y. Yan², M. Lee¹³, and R. D. Timmerman²; ¹University of Texas Southwestern Medical Center, Dallas, TX, ²Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, ³Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 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, ⁹University Hospitals Seidman Cancer Center, Case Western Reserve University, Cleveland, OH, ¹⁰Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, ¹¹University of California San Francisco, Department of Radiation Oncology, San Francisco, CA, ¹²Kidney Cancer Program, Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX, ¹³University of Texas Houston McGovern Medical School, Houston, TX

Purpose/Objective(s): We hypothesized that neurovascular element-sparing SAbR (NV-SAbR) would mitigate sexual quality of life (QoL) decline in men with localized prostate cancer.

Materials/Methods: A phase II RCT enrolled men planned for SAbR without ADT, intact sexual function, adequate hydrogel spacer placement and no dominant MRI lesion within 5 mm of one NV side. Patient-blinded randomization was 1:1 to SAbR (40 or 45 Gy/5 fractions) or NV-SAbR (unilateral NV de-escalation to 30 Gy). Accrual of 120 men provided 80% power at 2-sided significance a = 0.10 to detect a 10-point lesser difference in 2-year EPIC sexual summary score (-10 vs -20; standard deviation 20; attrition 15% for sample size 102). Secondary endpoints included EPIC-26 urinary/bowel QoL and CTCAE v4.0 GU/GI toxicity. Comparisons were made by Chi-square test for categorical variables and by t-test or Wilcoxon rank-sum test as appropriate for continuous variables.

Results: Of 120 men randomized, 119 received protocol treatment, and 102 had available EPIC data (see Table) at 2-years (50/59 NV-SAbR vs 52/60 SAbR). Mean age (64.2 vs 62, p = 0.13) and baseline sexual score (79.0 vs 80.8, p = 0.32) were balanced. For NV-SAbR vs SAbR, mean change from baseline in sexual score at 2 years did not differ significantly (-9.3±17.3 vs -12.6±16.9, p = 0.34), and erection quality (Q59) was answered “firm enough for intercourse” by 76% vs 81% of respondents. Among secondary endpoints, NV-SAbR demonstrated significantly better urinary incontinence scores at 2 years (median 100.0 vs 91.8, p < 0.01) and smaller decline from baseline (-1.40 ± 9.0 vs -7.8 ± 15.0, p = 0.01; minimal clinically important difference -6 point change 18% vs 41%, p = 0.01), including lower pad use (Q27: 0% vs 7.7%). No significant differences in 2-year GU/GI toxicity were observed between NV-SAbR vs SAbR: GU (Gr1 55.0% vs 42.1%, Gr2 27.3% vs 26.3%, Gr3 0% vs 1.8% p = 0.33); GI (Gr1 7.3% vs 8.8%, Gr2 0% vs 3.5%, p = 0.35).

Conclusion: NV-SAbR did not improve the 2-year primary sexual QoL endpoint. Notably, the control arm had substantially less decline than assumed in the trial design, with ~80% of men in both arms retaining erections sufficient for intercourse. NV-SAbR was associated with improved patient-reported urinary continence. These findings support continued evaluation of anatomy-sparing SAbR.

*EPIC Domain*	*SAbR*	*NV-SAbR*	*p-value*
*2 yr Scores* *Median (IQR); Wilcoxon rank-sum test* *[Respondents]*
Urinary Irritative	93.8 (81.3, 100.0) [50]	93.75 (87.5, 100.0) [50]	0.87
Urinary Incontinence	91.8 (76.1, 100.0) [51]	100.0 (91.8, 100.0) [49]	<0.01
Bowel	100.0 (95.8, 100.0) [52]	100.0 (91.7, 100.0) [50]	0.39
Sexual	71.0 (52.4, 82.7) [50]	71.2 (59.9, 80.3) [50]	0.96
*Change at 2 yr from Baseline* *Mean (SD); t-test* *[Respondents]*
Urinary Irritative	-3.1 (14.5) [48]	-4.0 (12.7) [50]	0.75
Urinary Incontinence	-7.8 (15.0) [51]	-1.4 (9.0) [49]	0.01
Bowel	-1.0 (6.5) [52]	-2.4 (6.7) [50]	0.27
Sexual	-12.6 (16.9) [50]	-9.3 (17.3) [50]	0.34