Main Session
Sep
28
QP 09 - Fewer Fractions, Greater Precision: Innovations in Prostate SBRT
LBA 21 - The ART of SABR: A Randomized Phase II Trial of Near "Margin-less" Adaptive Radiation Therapy (ART) Stereotactic Ablative Body Radiotherapy (SABR) for Primary Localized Prostate Cancer: Two vs. Five Fractions
Presenter(s)
Mark Waddle, MD - Mayo Clinic Rochester, Rochester, MN
M. R. Waddle1, B. J. Traughber Jr1, C. A. Dodoo2, J. M. Wilson1, A. W. Rajkumar3, T. D. Malouff1, B. J. Davis1, K. N. Lee1, J. L. Leenstra1, D. D. Chamberlain1, A. L. Stockham Jr1, B. J. Stish1, F. Mastroleo1,4, M. Borras-Osorio1, V. Malkov1, M. K. Lee3, and R. Phillips1; 1Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 2Mayo Clinic Department of Statistics, Scottsdale, AZ, 3Mayo Clinic, Rochester, MN, 4Division of Radiation Oncology, IEO, European Institute of Oncology, IRCCS, Milan, Italy
Purpose/Objective(s):
Ultra-hypofractionated stereotactic ablative body radiotherapy (SABR) is a safe and effective treatment of localized prostate cancer (CaP). Studies have demonstrated reduced acute toxicity and decrements in patient reported toxicity with margin reduction on an MR-based online adaptive platform; other studies found a two-fraction regimen feasible. The primary goal of this study was to evaluate the acute changes in patient reported outcomes with two-fraction SABR delivered with near margin-less CT-based online adaptive treatment versus standard of care five-fraction SABR.Materials/Methods:
Men with NCCN low- or intermediate-risk localized CaP were randomized 1:1 to either (Arm 1) online ART SABR delivered in two fractions with 1–2 mm planning target volume margins or (Arm 2) standard SABR delivered in five fractions with 3–5 mm margins. Iodinated hydrogel spacer was used in all patients, fiducial markers were optional. The primary endpoint was the change from baseline to 3 months post-treatment in patient-reported quality of life (QOL) using the EPIC-26 bowel and urinary irritative/obstructive domains. The study was powered for non-inferiority with a prespecified margin of 7 points. This interim analysis includes patients who completed baseline and 3-month EPIC-26 assessments. Mean change from baseline in bowel and urinary EPIC-26 domain scores are summarized by treatment arm. Between-group differences are presented with 97.5% confidence intervals. The trial remains ongoing and this analysis was not prespecified for efficacy testing, results are descriptive; no formal hypothesis testing was conducted. The final analysis will occur after full accrual.Results:
At the time of this interim analysis, 136 patients had been enrolled, 118 have started RT, and 38 and 35 were evaluated for the primary endpoint in Arms 1 and 2, respectively. The mean change in EPIC-26 bowel domain score at 3 months was -1.54 in Arm 1 versus -5.95 in Arm 2 (between-group difference 4.42, 97.5% CI [-0.90, 9.73]). The mean change in EPIC-26 urinary irritative/obstructive score at 3 months was -3.29 in Arm 1 versus -3.93 in Arm 2 (difference 0.64, 97.5% CI [-5.11, 6.39]). Rates of physician-reported grade =2 genitourinary and gastrointestinal toxicity within 3 months were 22.0% (13/59) for arm 1 patients and 27.1% (16/59) for arm 2 patients.Conclusion:
In this interim analysis, near margin-less online adaptive SABR delivered in two fractions appeared similar to early patient-reported bowel and urinary QOL compared with standard five-fraction SABR. As noted, these findings are preliminary. Definitive analysis and results are pending completion of accrual and follow-up.