Proton radiography using discrete range modulation method – A Monte Carlo study. (November 2022)

• Record Type: Journal Article
• Authors: Tsai, Yi-Chun; Fan, Kang-Hsing; Tsai, Tzung-Lin; Lee, Chung-Chi; Aso, Tsukasa; Wu, Shu-Wei; Lin, Chien-Yu; Tseng, Chien-Kai; Chen, Chia-Ray; Balaji, Selvaraj; Chao, Tsi-Chian
• Is Part Of: Radiation physics and chemistry. Volume 200(2022)
• Publication Date: 2022-11
• Subjects: Proton therapy -- Monte Carlo -- Proton radiography -- Range uncertainty -- Range modulation; Radiation chemistry -- Periodicals; Radiometry -- Periodicals; Radiation -- Periodicals; Chimie sous rayonnement -- Périodiques; 539.2
• DOI: 10.1016/j.radphyschem.2022.110279
• Languages: English
• ISSNs: 0969-806X

Abstract

Abstract: The advantage of proton therapy is the Bragg peak, but its range uncertainties can also lead to a certain dose deviation. This uncertainty can be reduced by using proton radiography to determine the water equivalent path length (WEPL). In this study, a discrete range modulation (DRM) method is introduced and its image quality compared with that of the previously reported continuous range modulation (CRM) method. MCNPX2.7.0 was used to simulate parallel proton beams with energies from 70 to 230 MeV at 2.5 MeV/step. In the DRM method, the WEPL can be related to R80 using the relationship between the proton energy and energy deposition at 80% of the fall-off (E80 ). For the CRM method, a dose gradient plan was created to estimate the relationship between WEPL and accumulated dose. DRM and CRM were compared using four different phantoms. For the slab, CIRS 062M head and cake phantoms, DRM had a good agreement with the theoretic WEPL: within 2 mm or 1%, and with a standard deviation of less than 0.5 mm. For the sphere phantom, DRM can achieve a GammapRG passing rate of 0.999, passing the criteria of a WEPL deviation of less than 2 mm and a distance-to-agreement of less than 3 mm. Proton radiographs made by the DRM method are more accurate and precise than those made by CRM. Two algorithms are proposed to solve the range mixing problems. DRM can also save unnecessary doses that do not contribute to imaging. Highlights: The WEPL determined using pRG reduces the uncertainty of the proton range. The DRM method can provide better image quality than CRM. Energy straggling and range mixing are two main causes of poor CRM image quality. Two algorithms are proposed to solve the range mixing problem. Compared to CRM, DRM saves unnecessary doses that do not contribute to imaging.