S1724
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Digital Poster 2045 Impact of dental materials on proton dose accuracy: experimental SPR measurements and TPS validation in SOBP and IMPT plan Sirinya Ruangchan 1,2 , Nattaporn Yamram 3 , Nakorn Phaisangittisakul 4 , Pipop Saikaew 5 , Anussara Prayongrat 1,2 , Tanawat Tawonwong 1,2 , Taweap Sanghangthum 3,2 1 Radiology, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand. 2 Her Royal Highness Princess Maha Chakri Sirindhorn Proton Center, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand. 3 Radiology, Chulalongkorn University, Bangkok, Thailand. 4 Physics, Chulalongkorn University, Bangkok, Thailand. 5 Operative and Endodontics, Mahidol University, Bangkok, Thailand Purpose/Objective: Dental materials can introduce uncertainties in proton range, affecting dose accuracy in head-and-neck radiotherapy (1). This study extended previous work (2) and aimed to experimentally determine the stopping-power ratios (SPRs) of common dental materials and to evaluate their impact on dose- calculation accuracy in treatment-planning systems (TPS) for spread-out Bragg peak (SOBP) and intensity- modulated proton therapy (IMPT) plans relevant to the head-and-neck region. Material/Methods: Figure 1 shows the experimental setup and the dental materials used in this study, including amalgam, zirconia, titanium, lithium disilicate, and resin composite. SPRs were measured with a multilayer ionization chamber. These values were overridden in a commercial TPS to compare dose distributions at different depths behind each dental material, calculated using default CT calibration versus experimental SPR data, and validated with film measurements. Box-shaped SOBP and IMPT fields were generated as simple plans in solid-water phantoms containing the test materials. In addition, IMPT plans were created in a CIRS head phantom embedded with high-density inserts (amalgam, zirconia, and titanium) to represent realistic head-and- neck configurations. Dose–volume histograms (DVHs) were analyzed for target coverage and doses to organs of interest.
plans, but not statistically significant. In addition, SPArc-variableshowed significantly better performance than IMPT and SPArc-original in sparing the heart (P<0.01 for D1%) and significantly better performance in sparing the left-and-right lungs(P<0.01 for V20Gy and V5Gy) than both IMPT and SPArc- original.In terms of delivery efficiency, the SPArc- variable shows prolonged treatment delivery time
compared to SPArc-original and superior to IMPT(SPArc-variable:434.99±52.95sec, IMPT:
506.47±14.65sec, P=0.02, SPArc- original:382.11±49.31sec, P=0.01).
Conclusion: This study introduces a novel SPArc optimization algorithm with a variable window to enhance dosimetric performance for the bilateral breast cancer patient population. More specifically, it reduces the dynamic delivery time compared to IMPT, while achieving equivalent target coverage and significantly superior heart and lungs sparing compared to IMPT and SPArc-original. References: 1. Cao, L. et al. Cardiac Substructure Dose Reduction and Toxicity Risk Assessment: IMPT Versus IMRT for Breast Cancer. Int J Part Ther17, 100752 (2025).2. Zhou, Y., Shi, Y., Wei, Y., Luo, Q. & Tang, Z. Nature-inspired algorithms for 0-1 knapsack problem: A survey. Neurocomputing554, 126630 (2023).3. Liu, G. et al. The first investigation of spot-scanning proton arc (SPArc) delivery time and accuracy with different delivery tolerance window settings. Phys. Med. Biol.68, 215003 (2023). Keywords: SPArc, variable tolerance window
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