Streamlined pin‐ridge‐filter design for single‐energy proton FLASH planning

• Published in: Medical physics (Lancaster) 2024-04, Vol.51 (4), p.2955-2966
• Main Authors: Ma, Chaoqiong, Zhou, Jun, Chang, Chih‐Wei, Wang, Yinan, Patel, Pretesh R., Yu, David S., Tian, Sibo, Yang, Xiaofeng
• Format: Article
• Language: English
• Subjects: proton FLASH; single‐energy planning; streamlined ridge filter
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1002/mp.16939

Background FLASH radiotherapy (FLASH‐RT) with ultra‐high dose rate has yielded promising results in reducing normal tissue toxicity while maintaining tumor control. Planning with single‐energy proton beams modulated by ridge filters (RFs) has been demonstrated feasible for FLASH‐RT. Purpose This study explored the feasibility of a streamlined pin‐shaped RF (pin‐RF) design, characterized by coarse resolution and sparsely distributed ridge pins, for single‐energy proton FLASH planning. Methods An inverse planning framework integrated within a treatment planning system was established to design streamlined pin RFs for single‐energy FLASH planning. The framework involves generating a multi‐energy proton beam plan using intensity‐modulated proton therapy (IMPT) planning based on downstream energy modulation strategy (IMPT‐DS), followed by a nested pencil‐beam‐direction‐based (PBD‐based) spot reduction process to iteratively reduce the total number of PBDs and energy layers along each PBD for the IMPT‐DS plan. The IMPT‐DS plan is then translated into the pin‐RFs and the single‐energy beam configurations for IMPT planning with pin‐RFs (IMPT‐RF). This framework was validated on three lung cases, quantifying the FLASH dose of the IMPT‐RF plan using the FLASH effectiveness model. The FLASH dose was then compared to the reference dose of a conventional IMPT plan to measure the clinical benefit of the FLASH planning technique. Results The IMPT‐RF plans closely matched the corresponding IMPT‐DS plans in high dose conformity (conformity index of