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PQA 04 - PQA 04 Palliative Care and Central Nervous System Poster Q&A

2493 - Efficacy and Safety of Magnetic Resonance-Guided Online Adaptive Stereotactic Radiotherapy in Oligometastatic Gynecologic Malignancies: A Multi-Institutional Outcomes Study

Monday, September 30, 2024
10:45 AM – 12:00 PM ET
Location: Hall C

Screen: 13

D. A. Cerbon1, E. Ozyar2, G. Ugurluer2, M. Tadross3, A. Rivera1, K. V. Albuquerque4, B. Atalar2, Y. Bolukbasi5, S. Corradini6, V. Demircan7, S. Han8, S. Lalondrelle9, A. Owrangi10, S. Patel11, I. M. Reis12, B. Thomas13,14, M. U. Abacioglu15, and L. Portelance1; 1Department of Radiation Oncology, University of Miami/Sylvester Comprehensive Cancer Center, Miami, FL, 2Department of Radiation Oncology, Acibadem MAA University, School of Medicine, Istanbul, Turkey, 3University of Miami, Miami, FL, United States, 4Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 5Amerikan Hastanesi, ISTANBUL, Turkey, 6Department of Radiation Oncology, University Hospital, LMU Munich, Munich, Germany, 7Gazi University Medical Faculty, Department of Radiation Oncology, Ankara, Turkey, 8Biostatistics and Bioinformatics Shared Resources, Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, FL, 9Department of Clinical Oncology, The Royal Marsden NHS Foundation Trust and Institute of Cancer Research London, London, United Kingdom, 10UT Southwestern Medical Center, Dallas, TX, 11Obstetrics, Gynecology and Reproductive Sciences at UT Health Houston, McGovern Medical School, Houston, TX, 12Department of Public Health Sciences and Sylvester Biostatistics/Bioinformatics Shared Resources (BBSR), University of Miami, Sylvester Comprehensive Cancer Center, Miami, FL, 13Royal Marsden NHS Foundation Trust, London, United Kingdom, 14Institute of Cancer Research London UK, London, United Kingdom, 15Department of Radiation Oncology Acibadem University, School of Medicine. Acibadem Altunizade & Atasehir Hospitals, Istanbul, Turkey

Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is an established treatment for most oligometastatic cancers. The challenge when treating oligometastatic GYN cancer (OGYNC) is metastases are commonly found near organs at risk (OAR). Therapeutic ratio may be improved using MR-guided radiation therapy (MRgRT) as it offers better soft tissue resolution and onboard adaptation, allowing for safe dose escalation on a mobile target or surrounded by mobile OARs. Few published prospective studies assess the role of Non-MRg SBRT in OGYNC. Reports of acute/late grade 2+ toxicity from the MITO retrospective cohorts range between 5-7%. Evidence for MRgRT in OGYNC is limited to small institutional series, and prospective outcomes using this technology have been reported only in a single institution stage I trial with 10 ovarian cancer patients. We report outcomes of the largest retrospective, multicenter cohort of MRgSBRT in patients with OGYNC. Materials/

Methods: We gathered data from 7 centers located in Miami, Dallas, Istanbul, London, and Munich, and included p</span>atients with OGYNC (= 5 metastases) treated by MRgSBRT w/wo online adaptation between January 2018 - July 2023. Primary endpoints were local control (LC) and Acute/late toxicities, recorded via version 5.0 of Common Terminology Criteria for Adverse Events (CTCAE). Secondary endpoints were progression free survival (PFS) defined as time from MRgSBRT to1st event: death, locoregional failure (using RECIST 1.1 criteria), or distant failure at 12 months, and overall survival (OS) at 12 months; both estimated using Kaplan-Meier method.
Results: We obtained data-sharing agreements and identified 81 patients (106 MRgSBRT courses) with a median follow-up of 15 months. Primary diagnoses were Ovary (n=41), Vagina (n=3), Uterine (n=26), Cervix (n=10). Sites treated included 28 RP lesions (26.4%), 15 intrabdominal (14.2%), 24 pelvic (22.6%), 10 vaginal (9.4%), 10 lung/mediastinal (9.4%), 17 liver/periportal lesions (16%), and 2 supraclavicular nodes (1.9%). Median GTV and PTV size was 8.14 cc (range 0.5-274cc) and 16.6 cc (2-487cc) respectively. Median prescription dose was 40 Gy (18-60 Gy) in a median 5 (1-10) fractions, and median BED10 of 72 Gy (28-180Gy). Ninety six MRgSBRT courses were adaptive (90%), of which 6.8% were due to motion management, 25.4% and 16.9% due to PTV or OAR violations respectively, and 32.2% due to violation of both. LC rate was 84.6%, of which 63.5% had complete response (Table 1). Estimated PFS and OS at 12 months were 48% (95% CI 36-59) and 91% (95% CI 81-96) respectively. Incidence of grade 2+ toxicity was 2.8% (2 grade 2 acute GI/GU events and 1 grade 3 vertebral fracture).
Conclusion: We provide the largest cohort to date of OGYNC treated with MRgSBRT, showing that dose escalation with this technology is feasible and well-tolerated with minimal toxicity and ~85% local control.
Local Control at 1 year (individual SBRT courses) N = 104 %
Complete Response 66 63.5
Partial Response 13 12.5
Stable Disease 9 8.7
Disease Progression 16 15.4