S2006
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Material/Methods: A retrospective planning study was performed on a patient with a 1400 cc CTV in the abdominal region. With 16 spheres the coverage ratio was 1.2%. Three non-coplanar plans with couch angles -10 and 10 degrees were created for a Varian TrueBeam 6 MV FFF. The first using target partitioning to determine segment shape and collimator angles, proceeding to MU-optimization. With each arc treating 3 targets and each target being treated from both couch angles, a minimum of 10 arcs is required. The other plans were VMATs with the same number of arcs optimized using the Grams strategy [2], one with leaf constraints and collimator angles determined by target partitioning. The prescription was 20 Gy to target sphere D50 (peak dose). Plans were compared by valley dose, defined as D50 in 5 mm spheres between targets in the different planes. Results: All strategies converged to highly modulated dose patterns. Valley dose in the sagittal and coronal planes was automatically low from beam geometry, but with a face-centered-cubic pattern rotated only in the transversal plane and limited couch kicks, neither plan reached <40% of prescription dose in the transversal valleys. Estimated treatment time was comparable between strategies at around 90s per beam. Target partitioning gave lower valleys in the coronal and sagittal planes, and VMAT optimization decreased valley dose in the transversal plane.
Figure 1: Segments from the three optimization strategies, transversal and coronal dose planes, transversal (left) and coronal (middle) line doses, DVH (right). Full line target partitioning + VMAT, dashed line target partitioning + segment weight optimization, dotted line VMAT without target partitioning, for treat spheres and Grams control structures. Conclusion: Target partitioning of lattice patterns isolated peaks in the cranio-caudial direction, but struggled in the transversal plane for the investigated face-centered- cubic sphere pattern and limited couch kicks. VMAT without target partitioning gave lower valleys in the transversal plane, but higher in the coronal and sagittal. References: [1] Duriseti S, Kavanaugh J, Goddu S, Price A, Knutson N, Reynoso F, Michalski J, Mutic S, Robinson C, Spraker MB. Spatially fractionated stereotactic body radiation therapy (Lattice) for large tumors. Advances in radiation oncology. 2021 May 1;6(3):100639.[2] Grams MP, Owen D, Park SS, Petersen IA, Haddock MG, Jeans EB, Finley RR, Ma DJ. VMAT grid therapy: A widely applicable planning approach. Practical radiation oncology. 2021 May 1;11(3):e339-47.[3] Sundström J, Finnson A, Hynning E, De Kerf G, Fredriksson A. Partitioning of multiple brain metastases improves dose gradients in single-isocenter radiosurgery. Med Phys. 2025 Oct;52(10):e18117. doi: 10.1002/mp.18117. PMID: 40973656. Keywords: Lattice: SFRT: target partitioning PTV coverage compromise in SBRT/SABR: an automated DICOM-based evaluation of PTV underdosage Martina Fassi 1,2 , Pietro Mancosu 2,3 , Laura Breschi 2 , Andrea Bresolin 2 , Pasqualina Gallo 2 , Francesco La Fauci 2 , Francesca Lobefalo 2 , Lucia Paganini 2 , Marco Pelizzoli 2 , Carlo Calissi 4,2 , Fabio Castellano 4,2 , Nicola Lambri 4,2 , Ciro Franzese 2,3 , Giacomo Reggiori 2,3 , Marta Scorsetti 2,3 , Stefano Tomatis 2 1 Dipartimento di Fisica e Astronomia Galileo Galilei, Università degli Studi di Padova, Padua, Italy. 2 Radiotherapy and Radiosurgery Department, IRCCS Humanitas Research Hospital, Rozzano, Italy. 3 Department of Biomedical Sciences, Humanitas University, Pieve Emanuele, Italy. 4 Dipartimento di Fisica Aldo Pontremoli, Università degli Studi di Milano, Milan, Italy Purpose/Objective: SBRT/SABR protocols often prioritise Organ Of Interest (OOI) over PTV coverage to reduce side effects. We developed a DICOM-based pipeline to automatically Digital Poster 4624
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