S1757
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Digital Poster Highlight 3776
LET by 0.06 keV/ μ m. As the number of beam fields increased, OAR LET exposure decreased substantially in LET-optimized plans without compromising tumor dose. The PAT LET-optimized plan showed a more favorable uniformity of LET distribution within the target volume and eduction in high-LET regions within OARs compared to 3-field, 4-field and 5-field IMPT plan, while minimum LET reduction remained relatively unchanged. Conclusion: This work demonstrates the feasibility and significant potential of LET-optimized PAT using ADMM for SRS. The method enables localized LET escalation within the tumor target while effectively reducing high-LET exposure to adjacent OARs. These findings support the application of LET-based biological optimization to improve therapeutic ratio for brain metastasis SRS.
Photon-Counting CT with DirectSPR for Direct Proton Therapy Planning on Contrast-Enhanced Images: A Phantom and Clinical Validation Study Wing Ki Claudia Chan, Bin Yang, Shu Ting Hung, Yeung Sum Wong, Geng Hui, Wai Wang Lam, Chin Chak Ho, Ka Keung Tang, Ting Chuan Li, Tin Lok Chiu, Kin Yin Cheung, Siu Ki Yu Medical Physics Department, Hong Kong Sanatorium & Hospital, Hong Kong, Hong Kong Purpose/Objective: Current proton therapy workflows require separate true non-contrast (TNC) CT scans to avoid iodine- induced stopping power ratio (SPR) prediction errors, increasing imaging dose and workflow complexity. While virtual non-contrast (VNC) imaging from dual- energy CT can mitigate this issue, it adds processing steps and potential uncertainties. DirectSPR technology predicts SPR with superior accuracy compared to conventional Hounsfield Unit (HU) conversion. This study investigates whether DirectSPR on photon-counting CT (PCCT) can achieve accurate SPR prediction in iodine contrast-enhanced regions, enabling direct proton therapy planning on contrast CT without VNC conversion. Material/Methods: A cylindrical solid water phantom (30 cm diameter) with inserts containing iodine concentrations from 0.2 to 10 mg/mL was scanned using a Siemens NAEOTOM Alpha PCCT simulator. Quantum plus protocols at 120 kVp and 140 kVp with full spectral capabilities, Qr40 kernel, quantum iterative reconstruction (strength 3), and iterative metal artifact reduction (iMAR) were applied to generate DirectSPR images. Two clinical patients (liver and brain tumors) were enrolled for dosimetric validation. Proton therapy plans were created on plain CT DirectSPR images following institutional protocols, then recalculated on post- contrast CT DirectSPR images. Key dosimetric parameters (CTV D95%, D0.03cc, V100%) and distal range differences were analyzed. Results: Phantom measurements demonstrated SPR stability across all iodine concentrations (0.3–16.3 mg/mL), with consistent predicted values of 1.012 ± 0.007 (range: 1.006-1.024) and 1.002 ± 0.005 (range: 0.998-1.009) for 120 and 140 kVp scan, respectively. This confirms DirectSPR's robustness against contrast agent interference. For both clinical cases, DirectSPR-based plans on contrast-enhanced CT showed minimal dosimetric deviations from plain CT plans: mean CTV HU difference<5, distal range shift <0.7 mm, and all dose metric deviations (D95%, D0.03cc, V100%) within 1%. These results indicate clinically acceptable accuracy for direct proton dose calculation on
References: 1. Boczkowski A, Kelly P, Meeks SL, Erhart K, Bova FJ, Willoughby TR. Proton vs Hyperarc radiosurgery: A planning comparison [published online ahead of print 20201105]. J Appl Clin Med Phys. 2020;21(12):96– 108.2. Fan QK, Zhang XY, Dao R, et al. Optimizing linear energy transfer distribution in intensity-modulated proton therapy using the alternating direction method of multipliers. Frontiers in Oncology. 2024;14.3. Lehrer EJ, Prabhu AV, Sindhu KK, et al. Proton and Heavy Particle Intracranial Radiosurgery. Biomedicines. 2021;9(1).4. Li X, Ding X, Zheng W, et al. Linear Energy Transfer Incorporated Spot-Scanning Proton Arc Therapy Optimization: A Feasibility Study [published online ahead of print 20210712]. Front Oncol. 2021;11:698537. Keywords: proton therapy, LET, stereotactic radiosurgery
Made with FlippingBook - Share PDF online