Radiotherapy quality assurance program of ongoing clinical trial using stereotactic ablative radiation therapy for recurrent ovarian cancer (SABR-ROC): a dummy run study of a prospective, randomized, multicenter phase III trial (KGOG 3064/KROG 2204).

Background: Recurrent ovarian cancer is often treated with chemotherapy, but many patients experience multiple recurrences with progressively shorter intervals and poorer prognosis. Repeated chemotherapy reduces patients' quality of life. Stereotactic Ablative Radiation Therapy for Recurrent Ovarian Cancer (SABR-ROC) (KGOG3064/KROG 2204) is an ongoing trial investigating the clinical efficacy of stereotactic ablative radiation therapy (SABR) for recurrent ovarian cancer. This study aimed to assess treatment planning consistency and protocol adherence in a prospective, randomized, multicenter phase III trial.

Methods: In this dummy run study of a prospective, randomized, multicenter phase III trial (SABR-ROC), we examined the variability in target delineation, dose prescription, and treatment planning among 10 centers participating in the SABR-ROC trial. Four representative cases, each presenting with different anatomical sites and treatment challenges, were selected for evaluation. Target volume consistency was measured using the Dice similarity coefficient, and treatment plans were reviewed to follow predefined goals and constraints in the protocol.

Results: Overall agreement in target delineation was low, with mean Dice similarity coefficients of 0.278 and 0.255 for gross tumor volume and planning target volume, respectively. Consistency was higher for cases involving lymph node and lung metastases but significantly lower for intraperitoneal and liver seeding metastases due to challenges in target delineation. Treatment plans generally adhered to protocol dose prescriptions, with minor deviations in planning target volume coverage, particularly in cases with multiple small metastases. Deviations from organ-at-risk constraints frequently occurred in cases involving small bowel proximity.

Conclusions: This study highlights the challenges in standardizing SABR for recurrent ovarian cancer, particularly in achieving a consensus on target delineation and balancing treatment efficacy with organ-at-risk safety. Clinician discretion remains essential in complex cases. The insights from this study will guide the development of standardized protocols to improve outcomes and reduce adverse effects in patients with recurrent ovarian cancer.

Trial Registration: This trial was registered with ClinicalTrials.gov under the identifier NCT05444270 on June 29, 2022.