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Evaluation of the dosimetric effect of scattered protons in clinical practice in passive scattering proton therapy

Authors
 Chankyu Kim  ;  Yeon-Joo Kim  ;  Nuri Lee  ;  Sang Hee Ahn  ;  Kwang Hyeon Kim  ;  Haksoo Kim  ;  Dongho Shin  ;  Young Kyung Lim  ;  Jong Hwi Jeong  ;  Dae Yong Kim  ;  Wook-Geun Shin  ;  Chul Hee Min  ;  Se Byeong Lee 
Citation
 JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS, Vol.22(6) : 104-118, 2021-06 
Journal Title
JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS
Issue Date
2021-06
MeSH
Computer Simulation ; Humans ; Monte Carlo Method ; Proton Therapy* ; Protons ; Radiometry ; Radiotherapy Dosage ; Radiotherapy Planning, Computer-Assisted
Keywords
aperture ; passive scattering ; proton therapy ; range compensator ; scattered protons ; snout
Abstract
The present study verified and evaluated the dosimetric effects of protons scattered from a snout and an aperture in clinical practice, when a range compensator was included. The dose distribution calculated by a treatment planning system (TPS) was compared with the measured dose distribution and the dose distribution calculated by Monte Carlo simulation at several depths. The difference between the measured and calculated results was analyzed using Monte Carlo simulation with filtration of scattering in the snout and aperture. The dependence of the effects of scattered protons on snout size, beam range, and minimum thickness of the range compensator was also investigated using the Monte Carlo simulation. The simulated and measured results showed that the additional dose compared with the results calculated by the TPS at shallow depths was mainly due to protons scattered by the snout and aperture. This additional dose was filtered by the structure of the range compensator so that it was observed under the thin region of the range compensator. The maximum difference was measured at a depth of 16 mm (8.25%), with the difference decreasing with depth. Analysis of protons contributing to the additional dose showed that the contribution of protons scattered from the snout was greater than that of protons scattered from the aperture when a narrow snout was used. In the Monte Carlo simulation, this effect of scattered protons was reduced when wider snouts and longer-range proton beams were used. This effect was also reduced when thicker range compensator bases were used, even with a narrow snout. This study verified the effect of scattered protons even when a range compensator was included and emphasized the importance of snout-scattered protons when a narrow snout is used for small fields. It indicated that this additional dose can be reduced by wider snouts, longer range proton beams, and thicker range compensator bases. These results provide a better understanding of the additional dose from scattered protons in clinical practice.
DOI
10.1002/acm2.13284
Appears in Collections:
1. College of Medicine (의과대학) > Dept. of Radiation Oncology (방사선종양학교실) > 1. Journal Papers
URI
https://ir.ymlib.yonsei.ac.kr/handle/22282913/190899
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