S2010
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
demonstrated using research treatment planning systems (TPS). The goal of this study was to implement and validate a script that generates fraction-variant treatments within a commercial TPS, enabling future
clinical translation. Material/Methods:
The script was developed using the Eclipse Scripting API. Starting from a manually generated reference plan, the field setup and planning objectives are automatically copied. Multiple plans, each to be delivered in only a subset of the fractions, are then sequentially optimized based on their cumulative physical dose, ensuring consistent target coverage while allowing plan-specific variations in aperture shapes and MU weights. A built-in module for plan complexity analysis was included to identify plans more likely to require patient-specific quality assurance (psQA) [2]. The script was validated for 10 patients with bilateral head-and-neck cancer. For each patient, five distinct 2-arc volumetric modulated arc therapy plans were generated to be delivered in seven fractions each (the prescription dose was 35 × 2 Gy for all patients, with simultaneous integrated boost). Results: Fraction-variant treatments were automatically generated in less than one hour, without manual intervention. While each individual plan in a fraction- variant treatment may be sub-optimal, their cumulative dose distribution resulted in excellent target coverage and improved normal tissue sparing (Figure 1).
Conclusion: In left-sided breast radiotherapy, using V5 guidance reduces low-dose irradiation of the ipsilateral lung but may increase cardiac and LAD exposure. When heart- sparing is prioritized, the need for V5 limitation should be carefully reconsidered in the context of contralateral breast and lung doses. Keywords: breast cancer, dose guidance, heart
Poster Discussion 4720
Towards clinical translation of fraction-variant radiotherapy for bilateral head-and-neck cancer Nathan Torelli, Madalyne Day, Riccardo Dal Bello, Jan Unkelbach Department of Radiation Oncology, University Hospital Zurich and University of Zurich, Zurich, Switzerland Purpose/Objective: Fraction-variant radiotherapy consists of delivering distinct plans across different fractions, thereby allowing to use a larger number of aperture shapes and monitor unit (MU) weights throughout the treatment course without increasing delivery time. Consequently, fraction-variant radiotherapy can achieve enhanced intensity modulation compared to conventional fraction-invariant approaches, resulting in an improved dosimetric quality [1]. However, fraction-variant radiotherapy has so far only been
For all patients, fraction-variant treatments improved target dose homogeneity (HI=D5/D95) and dose conformity (Paddick CI) compared to the corresponding fraction-invariant treatments (HI: 1.06±0.02 vs 1.07±0.02, CI: 1.00±0.03 vs 1.02±0.04), while achieving similar or better organs-at-risk sparing (mean dose to the pharyngeal constrictor muscles reduced by 1.8±1.2 Gy, mean dose to the ipsilateral parotid reduced by 0.6±0.5 Gy). The dosimetric results obtained for all patients are summarized in Figure 2.
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