S1962
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
1 Department of Oncology, University of Turin, Torino, Italy. 2 Data Science Unit, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy. 3 Medical Physics Department, IRCCS Regina Elena National Cancer Institute - IFO, Rome, Italy. 4 Research and Development, Tecnologie Avanzate, Turin, Italy. 5 Radiation Oncology, IRCCS Regina Elena National Cancer Institute - IFO, Rome, Italy Purpose/Objective: Propose a framework for optimising prostate re- irradiation plans based on NTCP, considering cumulative biologically-effective equivalent-uniform- doses (BE-EUDs) without requiring image or dose co- registration between different treatment sessions. Material/Methods: The framework directly operates on BE-EUDs to manage re-irradiation cumulative NTCP. For each at- risk organ, BE-EUD_1 is calculated from delivered dose–volume-histograms, corrected for fractionation. Organ-specific α / β and seriality parameters are used to preserve the radiobiological meaning of BE- EUD/NTCP. Optional time-dependent “dose discounts” account for recovery between treatments. Clinicians establish the maximum acceptable probabilities of side-effects after the second radiotherapy P_max. These indicate individual patient thresholds, which are based on balancing relapse control against side- effects. The total BE-EUD corresponding to P_max is determined using NTCP inverse formulation. The allowable contribution from the second course is calculated as max_BE-EUD_2 = max_BE-EUD_total − BE- EUD_1. This biologically safe BE-EUD_2 is converted into max_EUD_2 at the selected fractionation schedule for re-irradiation. The new plan is optimised by maintaining EUD<max_EUD_2, ensuring the toxicity risk remains acceptable. The framework conservatively assumes overlap between high-dose regions from both treatments and supports patient-specific dose- modifying factors. Anatomical uncertainties are implicitly managed by operating at the organ-level EUD. The framework was applied to ten prostate cancer re-irradiation cases, considering bladder (grade2+ haematuria, NTCP_model, Brand_2022) and rectum (grade2+ bleeding, NTCP model, Jongen_2025). To explore different risk–benefit scenarios, two P_max thresholds were tested: 20% (conservative) and 40% (permissive). The resulting plans were evaluated against the clinically delivered plans (manual) by assessing compliance with the prescribed dosimetric EQD2 goals derived applying co-registration. Results: Median interval between treatments was 7 years. Median BE-EUD_1 values: bladder 281.0 Gy ( α / β = 0.6 Gy) and rectum 130.9 Gy ( α / β = 2 Gy). At 𝑃 max=20%, allowable BE-EUD_2 was 273.4 Gy (bladder) and 70.3 Gy (rectum). At Pmax=40%, values increased to 340.7
Results: Introducing tools such as Batch Planning, Batch QA Calculation, Plan Check among others have demonstrated the scripts significant impact on process efficiency. These tools can improve the experience of professionals, freeing them from repetitive tasks and allowing them to focus more on clinical decisions. Beyond efficiency, the integration of scripts also enhances consistency and reliability in workflows. By automating standardized procedures, these tools mitigate the risk of human error, ensure compliance with established protocols, and provide a consistent framework for daily operations. This not only supports professionals in delivering safer, higher-quality patient care and outcomes but also fosters greater confidence in the overall process. Conclusion: The use of scripts in Elekta systems has proven to be an effective strategy for optimizing radiotherapy processes, promoting efficiency, safety, and standardization. These tools reduce the risk of human error and increase productivity, making them an essential resource for departments aiming to improve the quality of their services. However, implementation requires specific training and a collaborative and multidisciplinary approach between programmers and healthcare professionals in order to maximize the benefits of these technologies. In addition, scripts play a crucial role in fostering innovation within clinical practice. By enabling the customization of workflows and the automation of complex tasks, they empower institutions to adapt processes to their specific context while remaining aligned with international standards. This flexibility not only supports continuous improvement but also strengthens the integration of advanced technologies, paving the way for more precise and patient-centered treatments. References: 1. 1. Elekta Solutions AB. User Manual Monaco Scripting Reference Manual [Internet]. 2021. Available from: www.elekta.com.2. 2. Ford E, Conroy L, Dong L, de Los Santos LF, Greener A, Gwe-Ya Kim G, et al. Strategies for effective physics plan and chart review in radiation therapy: Report of AAPM Task Group 275. Med Phys. 2020 Jun 1;47(6):e236–72. Keywords: Scripting, Automation, Efficiency
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A non-coregistration NTCP-based framework for biologically guided prostate re-irradiation planning using cumulative Equivalent Uniform Dose Christian Fiandra 1 , Tiziana Rancati 2 , Erminia Infusino 3 , Marco D'Andrea 3 , Anna Ianiro 3 , Stefania Zara 4 , Claudio Vecchi 4 , Alessia Farneti 5 , Adriana Faiella 5 , Marta Bottero 5 , Antonella Soriani 3 , Giuseppe Sanguineti 5
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