S1782
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Conclusion: The commercial DLCT system provides robust, substantial RSP accuracy improvement over SECT. Sub-1% RMS error and consistency across conditions confirm suitability for clinical implementation, supporting reduced range uncertainty margins and eliminating calibration curve needs. Clinical adoption presents new challenges, like reduced RSP map contrast, requiring additional staff training for matching daily on-set images to the planning CT, and workarounds for importing RSP maps into treatment planning systems. Keywords: Relative stopping power, Dual-layer dual energy CT Fast conformal delivery of biologically optimized carbon ion plans: dosimetric, in vitro , and pre- clinical validations Sae Hyun Ahn 1,2 , Domenico Filosa 1 , Peter Lysakovski 3 , Stephan Brons 4 , Amir Abdollahi 1,5 , Jürgen Debus 1,3 , Thomas Tessonnier 1 , Andrea Mairani 1,4 1 Clinical Cooperation Unit Translational Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany. 2 Physics and Astronomy, Heidelberg University, Heidelberg, Germany. 3 Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany. 4 Radiation Oncology, Heidelberg Ion Beam Therapy Center, Heidelberg, Germany. 5 Radiation Onvology, Heidelberg University Hospital, Heidelberg, Germany Poster Discussion 4764 Purpose/Objective: Patient-specific range modulators (RMs) enable fast, conformal particle therapy delivery with monoenergetic beam plans, potentially reducing intrafractional motion sensitivity and facilitating UHDR and FLASH investigations. For carbon ions, whose relative biological effectiveness (RBE) varies steeply with depth, biological optimization of RM geometries is an essential step towards clinical translation, ensuring uniform biological effect across varying tissue depths. This work presents a stepwise translational framework for biologically optimized RMs (bio-RM), including dosimetric, biological, and patient-specific validations. Material/Methods: Comprehensive dosimetry was first performed using RMs designed to deliver uniform physical dose distributions. Measurements included a cubic target in water (4 cm SOBP) and a realistic target inside an anthropomorphic head phantom to evaluate dose conformity and depth-dose modulation in heterogeneous geometry. Subsequently, two bio-RM geometries were optimized using the clinical microdosimetric kinetic model (MKM) to generate 4 cm
RBE-weighted SOBPs. These geometries were 3D printed and used in monoenergetic carbon beam irradiations. Clonogenic survival was measured at three depths within each RBE-optimized SOBP and compared with MKM predictions. Finally, to evaluate clinical feasibility, a patient-specific bio-RM was designed and used to plan a single-field monoenergetic carbon treatment delivering 3 Gy(RBE) × 15 fractions to a brain tumor case. Results: Dosimetric verification in both water and the anthropomorphic head phantom (Figure 1) confirmed accurate depth-dose modulation and target conformity under homogeneous and heterogeneous conditions. MKM-based bio-RM designs produced flat RBE-weighted depth dose profiles that translated into consistent biological effects across varying depths (LET: 54 to 111 keV/µm) when irradiated monoenergetically. Measured survival in the SOBPs matched the model predictions within experimental uncertainties (Figure 2A). The patient case plan (Figure 2B-C) demonstrated that a patient-specific bio-RM can produce a comparable biological dose distribution to that of IMPT and meet the required clinical planning objectives.
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