S1987
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
all 160 patients' cohort was validated against the multicentric model following the same approach. Results: Table 1 shows data points outside prediction bands for internal (red), external, and multicentric validation across centers. Internal validation detected 17-21 heart points outside the band (42.5%-52.5%) and 14-18 for lung (35.0%-45.0%) per center. External validation revealed center C's model detected fewest points outside the band (heart: 1-7, lung: 0-8) compared to other centers' models, while center D's model detected most heart points outside the band (18-31). The multicentric model identified 16-27 heart points outside the band (40%-67.5%) and 7-32 for lung (17.5%-80%) across centers. Figure 1 shows the full data validation against the multicentric model, identifying 81 points (50.6%) and 68 points (42.5%) outside the band for heart and left lung respectively.
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Enhancing treatment plan quality across the Meditarrean region using multicentric Overlap Volume Histograms (OVH) for left breast Radiotherapy Farah Ben Hammouda 1,2 , Alessia Tudda 3 , Rita Buono 3 , Lotfi Ben Salem 4 , Raja Faraj ALmijbari 5 , Ismail Zergoug 6 , Roberta Castriconi 3 , Claudio Fiorino 3 , Marco Esposito 2,7 1 Physics department, Trieste University, Trieste, Italy. 2 Medical Physics, Abdus Salam International Center for Theoretical physics, Trieste, Italy. 3 Medical Physics department, IRCCS San Raffaele Scientific Institute, Milano, Italy. 4 Department of radiotherapy, Salah Azaiez Institute, Tunis, Tunisia. 5 Department of radiotherapy, National Cancer Center, Benghazi, Libya. 6 Medical physics department, Oncopole l'espoir, Oran, Algeria. 7 Medical physics Unit, Azienda sanitaria USL Toscana Centro, Firenze, Italy Purpose/Objective: Knowledge-based planning (KBP) employs dose prediction models to automate and standardize radiotherapy treatment planning. Models developed using single-center data may be prone to bias due to suboptimal plan quality and limited patient anatomical diversity. The objective of this study was to conduct a multicenter investigation involving institutions from various geographical regions across the Mediterranean to evaluate quality improvement potentials through KBP for left breast radiotherapy. Comparisons were made between single-center and multicenter models, and model transferability across different centers was assessed. Material/Methods: Planning data of 160 left breast patients, all treated by tangential field 3D-CRT technique, were randomly selected from four centers (A, B, C, D) in Italy, Algeria, Libya, and Tunisia. The Overlap Volume Histogram (OVH, R10%-R50%) for heart and left lung were generated by custom MATLAB 2024b code, to build dose prediction models employing linear regression against dosimetric parameters (D2%, D10%, D20%, D50%, Dmean). Doses were normalized to PTV D98% to account for different treatment strategies across centers. Since the OVH-DVH relationship reflects plan quality in terms of OAR sparing, models were developed using high-quality plans from each center (single center models) and all centers combined (Multicentric model), establishing geometric-based dose benchmarks. For heart and left lung, each center's data was validated against its own single- center model, the other three centers' models, and the multicentric model. Data points exceeding the upper band of each model (±1 σ ) represented model uncertainty in predicting DVH based on OVH. Finally,
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