ESTRO 2025 - Abstract Book

S849

Clinical - Gynaecology

ESTRO 2025

30 and 40 Gy (V10, V20, V30, V40, respectively), Dmean and Dmax were collected. Clinical data such as age, BMI, comorbidities, steroid and hormonal therapy before radiotherapy, menopausal state, smoking status, vitamin D and calcium dosage before and after treatment and diagnosis of osteopenia/osteoporosis on Bone Densitometry were analyzed. Results: A total of 202 patients were retrospectively analyzed. Thirty-six patients (17.8%) developed PIF in the treatment field, most asymptomatic. Our analysis shows that V40 Gy of LPBM is the most relevant dosimetric parameter; it was combined with age so we find a different risk of developing fracture depending on the V40 which takes into account the age of the patient. Conclusion: Our preliminary study allowed us to identify the following constraints to reduce the risk of PIF according to the age of patients. Further investigations are needed to confirm these findings through the inclusion of these parameters in the planning process. Poster Discussion Updates on Prospective Phase III Trial of Standard of Care Therapy With/Without Stereotactic Ablative Radiation Therapy for Recurrent Ovarian Cancer Yong Bae Kim 1,2 , Sangjoon Park 1 , Hojin Kim 1 , Chan Woo Wee 1 , Jung-Yun Lee 2 , Sokbom Kang 2 , Jae-Hoon Kim 2 1 Korean Radiation Oncology Group, Korean Radiation Oncology Group, Seoul, Korea, Republic of. 2 Korean Gynecological Oncologic Group, Korean Gynecological Oncologic Group, Seoul, Korea, Republic of Purpose/Objective: This ongoing phase III trial (NCT05444270) 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. Material/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, 130 (72.2%) 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 Keywords: Cervical cancer, pelvic insufficiency fractures 3182