2780 - Updates on Prospective Phase III Trial of Standard of Care Therapy with/without Stereotactic Ablative Radiation Therapy for Recurrent Ovarian Cancer
Presenter(s)
Y. B. Kim1, S. Park2, H. Kim3, C. W. Wee3, J. Y. Lee4, S. Kang5, and J. H. Kim4; 1Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea, Republic of (South), 2Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea, Republic of (South), 3Department of Radiation Oncology, Yonsei Cancer Center, Heavy Ion Therapy Research Institute, Yonsei University College of Medicine, Seoul, Korea, Republic of (South), 4Korean Gynecological Oncologic Group, Seoul, Seoul, Korea, Republic of (South), 5Korean Gynecological Oncologic Group, Kyungki-do, Kyungki-do, Korea, Republic of (South)
Purpose/Objective(s): This ongoing phase III trial evaluates whether adding stereotactic ablative radiotherapy (SABR) improves 3-year overall survival in patients with recurrent ovarian cancer. This study includes a dummy run to assess treatment planning consistency, protocol adherence, and feasibility across participating centers.
Materials/Methods: Patients with pathologically confirmed epithelial ovarian cancer who completed initial standard treatments were included. Additionally, patients with =10 metastases and maximum tumor diameter =5 cm are allowed. Randomization is stratified by (1) No. of the following clinical factors met: platinum sensitivity, absence of ascites, normal level of CA125, and ECOG performance status of 0–1 (0–3 vs. 4); (2) recurrence site: with vs. without lymph nodes; and (3) PARP inhibitor use vs. non-use. The target enrollment is 180 patients. Participants were randomized into two groups in a 1:2 ratio: the control arm receiving standard salvage therapy and the experimental arm receiving standard therapy plus SABR. The fraction number ranges from 1 to 10, and the accepted dose range is 16–45 Gy. A dummy run was conducted to validate target volume delineation, dose prescription, and treatment planning consistency across participating centers. Ten centers participated in this evaluation, using four representative cases encompassing different anatomical and therapeutic challenges, such as retroperitoneal lymph nodes, lung metastases, and intraperitoneal and liver seeding metastases. The consistency in target delineation was measured using the Dice similarity coefficient (DSC), focusing on protocol adherence and treatment uniformity.
Results: Currently, 138 (76.6%) patients have been enrolled across all centers. The dummy run revealed significant variability in target delineation, with mean DSC values of 0.278 for gross tumor volume (GTV) and 0.255 for planning target volume (PTV). Higher consistency was observed in lymph node and lung metastases cases, while intraperitoneal and liver seeding cases presented notable challenges due to anatomical complexity. Most treatment plans adhered to protocol standards, but deviations were often observed in organ-at-risk (OAR) constraints, particularly involving the small bowel. These findings emphasize variability in treatment planning and challenges in achieving uniformity for complex metastases.
Conclusion: The SABR-ROC trial is actively recruiting and is projected to meet its enrollment target by Q3 2025. The dummy run highlighted challenges in standardizing target delineation across centers, emphasizing the need for ongoing quality assurance and protocol refinement. Adhering to treatment protocols while balancing efficacy and OAR safety remains crucial. These insights aim to refine SABR protocols for recurrent ovarian cancer, enhancing treatment outcomes and safety. Clinical Trial number: NCT05444270.