1087 - Moderate Hypofractionated Boost to the Prostate with Pelvic Radiotherapy in High-Risk Prostate Cancer (MOB-RT): Early Outcomes from a Non-Randomized Phase II Trial
Presenter(s)
J. P. Bernstein1,2, J. Winter3, Z. Liu4, V. Kong5,6, J. Dang6, K. Wang6, P. Chung5, A. Bayley7, A. Berlin5, C. Catton5, E. Gutierrez8, A. Mesci3, A. McPartlin3, S. Raman6, S. Alibhai9, E. Taylor5, P. R. Warde5, and R. Glicksman3; 1University Health Network, Toronto, ON, Canada, 2Dalhousie University, Halifax, NS, Canada, 3Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, ON, Canada, 4Department of Biostatistics, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, 5Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 6Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, 7University of Toronto - Sunnybrook Odette Cancer Centre, Toronto, ON, Canada, 8IMSS, leon, Mexico, 9General Internal Medicine, UHN, Associate Professor of Medicine and Health Policy Management and Evaluation, University of Toronto,, Toronto, ON, Canada
Purpose/Objective(s): Moderate hypofractionation is a standard-of-care for patients with localized prostate cancer, however most studies evaluating moderate hypofractionation in the setting of elective nodal irradiation have treated the pelvic nodes with conventionally fractionated radiotherapy. Herein, we present the primary endpoint of a prospective clinical trial of moderate hypofractionation to the prostate and nodes
Materials/Methods: This was prospective single-institution single-arm study. Patients with high-risk or clinically node-positive (by conventional or molecular imaging) prostate cancer were eligible. Patients received 60 Gy in 20 fractions to the prostate and 48 Gy to the elective nodes, with simultaneous integrated boosts up to 68 Gy to intraprostatic gross tumor volume defined on multiparametric MRI and up to 55 Gy to radiographically-involved nodes, with long-term ADT. The primary endpoint was acute gastrointestinal (GI) toxicity (CTCAE v5.0) at 3-months following radiotherapy, with an a priori hypothesis that acute grade >2 gastrointestinal (GI) toxicity would not exceed 35% based on published literature. Secondary endpoints included genitourinary (GU) toxicity and quality of life (QOL). Univariable analysis was performed to identify predictive factors; to avoid collinearity, multivariable analysis was not conducted
Results: One-hundred patients were enrolled, and 97 underwent protocol-specified treatment and were eligible for analysis. Median age was 73 years, 49% had grade group 4-5 disease, median PSA was 22.2 ng/mL, 76% were cT1c-2, and 21% were cN1. Twenty-three (24%) patients received intraprostatic boost and eighteen (19%) had nodal boost. All patients reached the 3-month follow-up timepoint. Fifteen patients (15.5%) experienced acute grade >2 GI toxicity, and the 95% Clopper-Pearson confidence interval was 0-22.8% (p <0.001); the upper bound of the confidence interval was below the pre-set threshold of 35%, and non-inferiority was satisfied. Higher dose to rectum (D1cc, p=0.009), small bowel (D1cc, p=0.022; D5cc, p=0.015) and large bowel (D1cc, p=0.022; D5cc, p=0.03), and use of intraprostatic boost (p=0.031) were associated with higher odds of grade >2 GI toxicity. One patient (1%) experienced grade 3 GI toxicity. Twenty-six (27%) patients experienced grade >2 GU toxicity, with no grade >3 GU toxicities, and no dosimetric predictors of GU toxicity. Nodal boost was not significantly associated with toxicity. All patients completed QOL questionnaires at baseline and 3 months. There were no statistically significant changes in GI or GU QOL scores at 3-months post treatment
Conclusion: Moderately hypofractionated RT to the prostate and pelvic nodes was associated with low rates of acute GU and GI toxicity and resulted in no detriment to QOL. Longer follow- up is needed for other key secondary endpoints. Ongoing studies assessing the role of ultrahypofractionated stereotactic body radiotherapy to the prostate and nodes are underway