S1772
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Conclusion: The new robust optimization method preserves robustness while improving lattice characteristics. Shoot-through enhanced proton arc plans could further enhance results. References: [1] Mossahebi et al. Clinical Implementation and Dosimetric Evaluation of a Robust Proton Lattice Planning Strategy Using Primary and Robust Complementary Beams. Int J Radiat Oncol 2024. [2] Engwall et al. Shoot - through layers in upright proton arcs unlock advantages in plan quality and range verification. Med Phys 2025.[3] Wu et al. The Technical and Clinical Implementation of LATTICE Radiation Therapy (LRT). Rad Res 2020. Keywords: lattice, spatially-fractionated RT, shoot- through Development and evaluation of a contacted range shifter for proton therapy: impact of air gap and clinical feasibility Bharinee Promprakob 1 , Jaruek Kanphet 2,3 , Taweap Sanghangthum 1,3 , Sirinya Ruangchan 2,3 1 Radiology, Chulalongkorn University, Bangkok, Thailand. 2 Radiology, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand. 3 Her Royal Highness Princess Maha Chakri Digital Poster 4256 Sirindhorn Proton Center, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand Purpose/Objective: Proton therapy offers precise dose delivery for head- and-neck cancers but requires a range shifter for superficial targets. The use of a range shifter introduces challenges in maintaining a minimal air gap, which is essential for controlling spot size and ensuring accurate dose calculation (1,2). Therefore, this study aims to develop a prototype contacted range shifter (CRS) to minimize the air gap and evaluate its proton beam characteristics for clinical implementation. Material/Methods: Air gaps of 5–42.1 cm were tested to evaluate spot size in air and in a phantom using proton energies of 80– 200 MeV through FLUKA Monte Carlo (MC) simulations, a treatment planning system (TPS), and measurements. The phantom study further examined spot size with depth and energy. For CRS development, materials were assessed for relative linear stopping power (RLSP) using MC simulations and a multi-layer ionization chamber. Acrylic was selected to fabricate a box-shaped CRS prototype. Dose calculations using a CIRS head phantom
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