S421
Clinical - Gynaecological
ESTRO 2026
Milan, Italy. 6 Radiation Oncology Center, S Maria Hospital, Terni, Italy. 7 Department of Radiation Oncology, IRCCS San Raffaele Scientific Institute, Milan, Italy. 8 Department of Radiotherapy and Radiosurgery, IRCCS Humanitas Research Hospital, Milan, Italy. 9 Radiation Oncology Unit, “Vito Fazzi” Hospital, Lecce, Italy. 10 Radiation Oncology Unit, Ospedale degli Infermi, Biella, Italy. 11 Radiation Oncology, Department of Medical and Surgical Sciences (DIMEC), University of Bologna, Bologna, Italy. 12 Operative Research Unit of Radiation Oncology, Fondazione Policlinico Universitario Campus Bio-Medico, Rome, Italy. 13 Radiation Oncology Unit, Azienda Ospedaliero Universitaria Careggi, University of Florence, Florence, Italy. 14 Radiation Oncology Section, Perugia General Hospital, Perugia, Italy. 15 Radiation Oncology Unit of Arezzo-Valdarno, Azienda USL Toscana sud est, Arezzo, Italy. 16 Radiation Oncology Unit, UPMC Hillman Cancer Center San Pietro FBF, Rome, Italy. 17 Radiotherapy Oncology, Department of Medicine and Surgery and Translational Medicine, Sapienza University of Rome, S. Andrea Hospital, Rome, Italy. 18 Radiation Oncology Unit, Department of Oncology, “Santa Maria della Misericordia” University Hospital, Azienda Sanitaria Universitaria Friuli Centrale, Udine, Italy. 19 Department of Radiation Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori di Milano, Milano, Italy. 20 U.O. di Radioterapia Oncologica "Guido Berlucchi", Fondazione Poliambulanza Istituto Ospedaliero, Brescia, Italy. 21 Radiation Oncology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy. 22 Istituto di Radiologia, Università Cattolica del Sacro cuore, Rome, Italy. 23 Department of Maternal and Child Health, Obstetrics and Gynecology Clinic, University Hospital of Udine, Udine, Italy. 24 Department of Medicine (DMED), University of Udine, Udine, Italy. 25 Uro-Gynecological Department, National Cancer Institute of Naples Fondazione G Pascale IRCCS, Naples, Italy
Purpose/Objective: Stereotactic body radiotherapy (SBRT) achieves high local control in oligometastatic gynecologic malignancies, yet predictors of treatment-related toxicity remain uncertain. This study aimed to identify clinical and dosimetric determinants of acute and late toxicity and to quantify the predictive value through statistical and machine-learning models. Material/Methods: A retrospective analysis was conducted on patients with cervical, endometrial, or ovarian oligometastatic disease enrolled in the MITORT-1 and MITORT-2 trials [1–3]. Toxicity was assessed according to CTCAE v5.0 and categorized as acute ( ≤ 90 days) or late (>90 days). Lesion-level predictors were assessed using generalized linear mixed-effects models (GLMM) with a random intercept for each patient. Variables included dose (BED ₁₀ , BED ₃ ), Planning Tumour Volume (PTV), fractionation schedule, tumor type, and anatomic site. Complementary machine- learning algorithms (Random Forest, XGBoost, GLMNet) explored non-linear associations. Model performance was evaluated via patient-grouped cross- validation (AUC, sensitivity, precision). Results: Toxicity data were collected from 820 SBRT- treated lesions in 483 patients. Overall, 21% of lesions were associated with any-grade toxicity (16% acute, 4% late, 1.5% both). Lesion-level analysis identified the irradiated anatomic site as the only significant predictor of acute toxicity (p < 0.002), with the highest risk observed for abdominal and pelvic lesions. None of the evaluated dosimetric parameters (BED ₁₀ , BED ₃ , PTV) showed an independent association (all p > 0.1). No variable significantly correlated with late toxicity.At the patient level, tumor type was a significant predictor of any toxicity (p = 0.03), with ovarian cancers showing a nearly threefold higher risk than cervical cancers (OR ≈ 2.7, 95% CI 1.2–6.6). The GLMM
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