S488
Clinical - Gynaecological
ESTRO 2026
Purpose/Objective: To investigate the impact of nodal
rectum in cervical cancer radiotherapy. Interfractional organ variations led to significantly higher accumulated doses than planned, influencing toxicity outcomes. Incorporation of daily imaging, adaptive planning, and online dose correction may improve dosimetric precision and reduce treatment-related morbidity. References: Tyagi N,Lewis J.H.,Yashar C..Vo D. ,JiangS.B.,Mell L.K..Daily Online Cone Beam Computed Tomography to Assess Interfractional Motion in Patients With Intact Cervical Cancer.International Journal of Radiation Oncology 2011 May;80(1):273- 280Deville C, Both S, Hwang W, Tochner Z, Vapiwala N. Clinical Toxicities and Dosimetric Parameters After Whole-Pelvis Versus Prostate-Only Intensity-Modulated Radiation Therapy for Prostate Cancer. International Journal of Radiation Oncology*Biology*Physics. 2010;78(3):763- 772. Keywords: cumulative dose, VMAT, toxicity Digital Poster 4845 Impact of nodal characteristic and treatment technique on failure patterns in cervical cancer IGABT-based chemoradiotherapy: A competing risk analysis Sittiwong Wiwatchai 1,2 , Pittaya Dankulchai 1,2 , Tissana Prasartseree 1,2 , Akrapol Suppasedtanon 1 , Natthanicha Sauenram 1 , Naritsa Rotmuenwai 1 , Pongpop Tuntapakul 1 , Wajana Thaweerat 1 , Pitchayut Wongsuwan 1 , Ratchapas Romrattaphan 1 , Nantakan Apiwarodom 1 , Yaowalak Chansilpa 1 1 Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand. 2 Siriraj Brachytherapy Center (SiBTC),, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
characteristics and treatment techniques on patterns and predictors of nodal failure and distant metastasis in patients with locally advanced cervical cancer (LACC) treated with image-guided adaptive brachytherapy (IGABT)-based concurrent chemoradiotherapy (CCRT). Material/Methods: This retrospective study included 188 patients with FIGO 2018 stage IB3–IVA LACC treated with definitive CCRT comprising weekly cisplatin and external beam radiotherapy (EBRT, 45–50 Gy), followed by 3D image-guided adaptive brachytherapy (3D-IGABT). Whole-pelvic radiotherapy (WPRT) or extended-field radiotherapy (EFRT) was delivered according to nodal involvement. Nodal boosts were administered using either a Simultaneous Integrated Boost (SIB) or Sequential technique. Local–regional failure (LRF) and distant metastasis (DM) were analyzed using Fine–Gray competing risks regression, treating death or the alternate failure type as competing events. Subhazard ratios (SHR) and 95% confidence intervals (CI) were calculated to identify predictors. Variables with clinical relevance or p < 0.10 in univariate analysis were included in multivariable models. Interaction terms were evaluated for SIB × Sequential (LRF) and EFRT × para-aortic involvement (DM). Statistical significance was set at p < 0.05. Results: The median follow-up was 26 months (IQR 18–35). Most patients had stage IIIC1 (39.9%) or IIIC2 (19.1%) disease. WPRT and EFRT were delivered in 67.1% and 32.9% of patients, respectively. The median number of boosted lymph nodes was 3 (range 1–30) for pelvic and 4 (range 1–42) for para-aortic regions, with mean diameters of 1.3 cm and 0.9 cm, respectively. SIB was used in 82.4% of patients and Sequential boosts in 17.6%. Two-year locoregional recurrence-free survival (LRFS) and distant metastasis-free
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