S1785
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
proton therapy if Δ NTCP>5% on the initial CT. After plan adaptation, patients were re-evaluated to assess whether switching to photon therapy would maintain Δ NTCP<5% relative to a proton-only treatment. An optimization algorithm was then developed to reallocate the freed proton treatment slots across the entire patient cohort to minimize the mean NTCP at the population level. Results: At baseline, 11 of 20 patients met the Δ NTCP>5% criterion and would have been referred for proton therapy. After tumor shrinkage and plan adaptation, 10 of these patients could have safely switched to photon therapy while maintaining Δ NTCP<5% (Figure 1), thereby freeing a total of 111 proton treatment slots.
Conclusion: Anatomical changes during treatment, particularly tumor shrinkage, may substantially affect the relative benefit of proton versus photon therapy. Adapting treatment modality mid-course can preserve clinical outcomes while freeing valuable proton resources. Optimizing the reallocation of these resources can enhance the overall benefit of proton therapy at the population level. References: [1] Niezink, A. G. H., van der Schaaf, A., Wijsman, R., Chouvalova, O., van der Wekken, A. J., Rutgers, S. R., Pieterman, R. M., van Putten, J. W. G., de Hosson, S. M., van der Leest, A. H. D., Ubbels, J. F., Woltman-van Iersel, M., Widder, J., Langendijk, J. A., & Muijs, C. T. (2023). External validation of NTCP-models for radiation pneumonitis in lung cancer patients treated with chemoradiotherapy. Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology, 186, 109735. https://doi.org/10.1016/j.radonc.2023.109735. Keywords: Proton slot allocation, NTCP, lung cancer Poster Discussion 4930 Mitigating metal-induced artefacts in pencil beam scanning proton therapy using multiple CT modalities. Claudine HOFVERBERG 1 , Luka McNeill 1 , Ronan Penard 1 , Axel Bernabe 1 , Régis Amblard 1 , Jean Gasteuil 1 , Louis Marage 1 , Baptiste Lhomel 1 , Pasqualina Gallo 2 , Andrea Bresolin 2 , Chiara Radice 2 , Benjamin Serrano 1 , Pietro Mancosu 2,3 , Daniel Maneval 1 1 Medical Physics Department, Centre Antoine Lacassagne, Nice, France. 2 Radiotherapy and Radiosurgery Department, IRCCS Humanitas Research Hospital, Milan, Italy. 3 Biomedical Sciences Department, Humanitas University, Milan, Italy Purpose/Objective: Metallic implants generate severe artefacts in CT imaging, compromising delineation and dose calculation accuracy in proton therapy. Comparative evaluation of CT technologies is essential to identify optimal imaging strategies for robust treatment
Optimal reallocation of these slots allowed 16 of 20 patients to receive at least a partial proton course, achieving NTCP reductions of up to 2.6% for individual patients (Figure 2). The average NTCP across the entire cohort decreased from 4.2±2.4% to 4.0±2.2%.
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