S1760
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
(mean=1.1%) , ∆ V95%<2.5% (mean=0.3%)). Robustness analysis revealed no relevant differences between DTU and clinical plans. Performance did not worsen with longer intervals between diagnostic and planning imaging, although in a clinical implementation diagnostic images acquired within ~1–2 months would likely be preferred. Conclusion: Within an adaptive framework, skipping the pCT and initiating PT planning directly from diagnostic imaging is dosimetrically feasible for the sites studied. If implemented, DTU could remove one hospital visit, shorten time to start treatment, and enable earlier proton-photon planning comparisons at diagnosis. References: M. Li, X. Li, S. Safai, A. J. Lomax, and Y. Zhang, “Diffusion Schrödinger bridge models for high - quality MR - to - CT synthesis for proton treatment planning,” Med Phys, vol. 52, no. 7, Jul. 2025, doi: 10.1002/mp.17898. Keywords: Direct-To-Unit,diagnostic-based planning,workflow Digital Poster Highlight 3921 Dirty Dose and Linear Energy Transfer: Complementary Metrics for Proton Therapy Planning Aleksandr Vanchugov 1 , Anna M. Flejmer 2,3 , Erik Traneus 4 , Iuliana Toma-Dasu 5,6 , Alexandru Dasu 1,3 1 The Skandion Clinic, The Skandion Clinic, Uppsala, Sweden. 2 Department of Immunology, Uppsala University Hospital, Uppsala, Sweden. 3 Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden. 4 RaySearch Laboratories, RaySearch Laboratories, Stockholm, Sweden. 5 Oncology Pathology Department, Karolinska Institutet, Stockholm, Sweden. 6 Medical Radiation Physics, Stockholm University, Stockholm, Sweden Purpose/Objective: While a constant relative biological effectiveness (RBE) of 1.1 is commonly assumed in proton therapy, the RBE increases with the linear energy transfer, potentially leading to unexpected toxicities. This study investigates the relationship between dose-averaged Linear Energy Transfer (LETd) and Dirty Dose (DD) – defined as the dose delivered by particles with LET > 3 keV/µm – to assess their impact on treatment plan evaluation and field arrangement strategies. Material/Methods: A virtual cylindrical phantom with a centrally located target and CT datasets of 10 previously treated patients were used in this study. For each patient, 10 robustly optimized (3%,3mm) plans with 2-7 fields were created in RayStation treatment planning
independently of the clinical ones.Next, to mimic day-1 adaptive DTU, the diagnostic-based template plan was re-optimized on the pCT (surrogate for the first fraction CT), creating the DTU plan (Figure 2). Finally, DTU and clinical plan were compared for target coverage (CTV D98%, V95%, mean dose), organ-at-risk (OAR) endpoints (vs clinical thresholds or clinical-plan
values), and robustness.
Results: Across all DTU plans, 93% of OAR and 96% of target goals were met, with the remaining goals deviating by less than 5%
from their thresholds. Target coverage was maintained (difference in ∆ D98%<5%
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