3278 - CT-Guided Adaptive SBRT with Simultaneous Integrated Boost for Prostate and Pelvic Nodes in High-Risk and Unfavorable Intermediate-Risk Prostate Cancer: Interim Analysis
Presenter(s)
W. Liu1, D. Hong2, M. Mahmood3, V. Sviderskiy4, M. R. Waters5, J. P. Schiff6, K. Kiser7, Y. Huang3, B. Strickland8, T. Minor8, C. Phillips8, E. Marshall8, L. Brunt9, L. Mayer10, C. Welch8, L. E. Henke11, E. Laugeman2, R. Beckert2, J. W. Randall12, J. M. Michalski13, B. C. Baumann14, H. A. Gay13, and A. K. Bhatt15; 1University of Iowa, Iowa City, IA, 2WashU Medicine, Department of Radiation Oncology, St. Louis, MO, 3Washington University School of Medicine in St. Louis, Department of Radiation Oncology, St. Louis, MO, 4NYU Grossman School of Medicine, New York, NY, 5Virginia Commonwealth University Health System, Richmond, VA, 6Tulane University School of Medicine, New Orleans, LA, 7MD Anderson Cancer Center, Houston, TX, 8Washington University in St. Louis School of Medicine, Saint Louis, MO, 9Washington University in St. Louis, St. Louis, MO, 10Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO, 11Department of Radiation Oncology, University Hospitals Seidman Cancer Center, Case Western Reserve University, Cleveland, OH, 12Department of Radiation Oncology, Northwestern University, Chicago, IL, 13Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 14University of Pennsylvania, Philadelphia, PA, 15Karmanos Cancer Institute at McLaren Greater Lansing, Lansing, MI
Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is increasingly used to treat high-risk prostate cancers. While SBRT has acceptable toxicity, larger elective nodal volumes required to treat higher-risk prostate cancer remains a concern. Preliminary studies show that CT-guided online adaptive SBRT improves target coverage and reduces doses to organs-at-risk (OAR). This prospective study will evaluate toxicities and quality of life (QoL) in unfavorable intermediate- and high-risk prostate cancer patients treated with CT-guided online adaptive SBRT to the prostate and regional nodes.
Materials/Methods: Patients with unfavorable intermediate- or high-risk prostate adenocarcinoma were enrolled in this IRB-approved single arm prospective trial from February 2023 to present. Treatment includes four targets with a simultaneous integrated boost (SIB): 50 Gy to MRI-detected lesions, 40 Gy to the prostate and gross nodal or extraprostatic disease, 36.25 Gy to the prostate and proximal seminal vesicles, and 25 Gy to the elective pelvic nodes, delivered in 5 fractions over 5 weeks. All treatments were conducted on the technology company system using online adaptive SBRT approach. Time on table was recorded by radiation therapists. Acute gastrointestinal (GI) and genitourinary (GU) toxicities were assessed using CTCAE v5. Patient-reported QoL were measured using EPIC-26 and EQ-5D-5L questionnaires at baseline, end of treatment, and 3 months post-treatment.
Results: Of 17 patients currently enrolled on study, 15 have completed 1 adaptive fraction, and 9 have completed treatments. 12 had high-risk prostate cancer and 5 had unfavorable intermediate risk. The median age is 70 years (56-77), and the median baseline ECOG score is 0 (0-1). 97% (63/65) of fractions required adaptation to meet OAR constraints and/or maintain PTV coverage. Average treatment time was 56 minutes (39-83). No Grade 3 toxicities were reported. From baseline to end of treatment, three Grade 2 and five Grade 1 GU toxicities including dysuria, urinary frequency, and urinary retention were recorded. Three Grade 1 GI toxicities including diarrhea and rectal discomfort were also recorded. From end of treatment to 3 months post treatment, three Grade 1 GU toxicities were reported. EPIC-26 urinary obstruction (UO) scores showed decline of 21 points (6-35) from baseline to end of treatment (p=0.003) and recovery of 20 points (1-40) from end of treatment to 3 months post treatment (p=0.03). No statistical differences were observed for other Epic-26 domains or EQ-5D-5L scores between different time points.
Conclusion: Patients with unfavorable intermediate or high-risk prostate cancer treated with CT-guided online adaptive SBRT with elective nodal coverage and 50Gy SIB to MR-detected lesions did not experience any Grade 3 toxicities during or after treatment. QOL UO scores decreased at the end of treatment but recovered at the 3-month follow-up. This interim analysis suggest this approach is safe and well tolerated.