ESTRO 2025 - Abstract Book

S1788

Clinical – Upper GI

ESTRO 2025

that increasing the low-to-intermediate dose area in the lungs further raises the risk, even when this increase reduces the high dose area in the heart. Considering the dose effect and good calibration, this model can be used for treatment optimization and RT-technique selection, offering a promising avenue for reducing pneumonia risk in future EC patients.

Keywords: NTCP-model, Pneumonia, Oesophageal cancer

References: [1] de Jong VMT, Moons KGM, Eijkemans MJC, Riley RD, Debray TPA. Developing more generalizable prediction models from pooled studies and large clustered data sets. Statistics in Medicine 2021;40:3533–59. https://doi.org/10.1002/sim.8981.

2077

Digital Poster Hepatic metastases SBRT: what can CECT features tell us about outcome prediction and follow up? A single center retrospective study Alessandro Biscarini 1 , Silvia Ruggeri 1 , Linda Calistri 1 , Maria Pisano 1 , Gabriele Simontacchi 2 , Michele Aquilano 3 , Mauro Loi 2 , Daniela Greto 2 , Isacco Desideri 2 , Pietro Garlatti 2 , Luca Visani 2 , Monica Mangoni 2 , Alessandra Galardi 2 , Pierluigi Bonomo 2 , Andrea Romei 2 , Giulio Frosini 2 , Ilaria Morelli 2 , Luca Burchini 2 , Marco Banini 2 , Marianna Valzano 2 , Dora Cela 2 , Stefania Pallotta 4 , Marta Casati 4 , Lorenzo Livi 2 , Cosimo Nardi 1 1 Department of Experimental and Clinical Biomedical Sciences, Radiodiagnostic Unit n.2,University of Florence, Azienda Ospedaliero-Universitaria Careggi, Florence, Italy. 2 Radiation Oncology, Azienda Ospedaliero Universitaria Careggi, University of Florence, Florence, Italy. 3 Cyberknife Center, Istituto Fiorentino di Cura e Assistenza (IFCA), Florence, Italy. 4 Medical Physics Unit, Azienda Ospedaliero Universitaria Careggi, Florence, Italy Purpose/Objective: This study aims to investigate how morphological, dimensional and contrast enhancement CT features can inform the selection for Stereotactic Body RadioTherapy (SBRT), predict the outcome and aid the early post-radiotherapic treatment approach to liver metastases. Material/Methods: Data from 40 patients with 54 liver metastases treated with SBRT were restrospectively extracted from multiphasic contrast enhanced CT (CECT) before SBRT (T0) and after 3 months (T1). Patients with less than 6 months of CECT follow up evaluation or patients with target lesion not adequately assessable on follow up investigations (e.g. due to fiducial artifacts) were excluded from the study. To evaluate treatment response, we categorized radiotherapy treated secondary lesions into two groups: responders and non-responders. The responder group comprised all metastases that exhibited volumetric reduction, dimensional stability (growth <20%), or pseudoprogression (a transient increase in size followed by a decrease or dimensional stability) during the follow up period (up to 12 months) compared to T0 volume. The non-responder group included all lesions that showed true progression or recurrence localized at the borders of the lesion within the follow-up period. Clinical and radiological data (longest diameter, volume, mean density) extracted from multiphasic CECT at T0 and T1 were compared between these two groups. Results: Among non-responders (20 lesions), 59.3% had a Biological Equivalent Dose (BED) value <100 compared to only 14.8% with a BED >100 (p=0.002). At baseline (T0), responder lesions had a significantly smaller mean diameter (24.015 mm) compared to non-responders (31.689 mm) (p=0.25), as well as a smaller volume (4227.133 mm^3 vs. 7651.481 mm^3, p=0.03). Regarding contrast enhancement characteristics, non-responders showed a lower mean density (in Hounsfield Units) compared to responders in both arterial and venous phases (p=0.028 and p=0.021,