Collection efficiency of a monitor parallel plate ionization chamber for pencil beam scanning proton therapy  

作　　者：Rong-Cheng Han Yong-Jiang Li Yue-Hu Pu 

机构地区：[1]Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Shanghai 201800,China [2]University of Chinese Academy of Sciences,Beijing 100049,China [3]Shanghai APACTRON Particle Equipment Co.Ltd,Shanghai 201800,China [4]Shanghai Advanced Research Institute,Chinese Academy of Sciences,Shanghai 201210,China

出　　处：《Nuclear Science and Techniques》2020年第2期1-10,共10页核技术（英文）

摘　　要：The collection efficiency of monitor parallel plate ionization chambers is the main uncertainty in the beam control of pencil beam scanning systems.Existing calculation methods for collection efficiency in photon or passive scattering proton systems have not considered the characteristics of non-uniform charge density in pencil beam scanning systems.In this study,Boag’s theory was applied to a proton pencil beam scanning system.The transverse distribution of charge density in the ionization chamber was considered to be a Gaussian function and an analytical solution was derived to calculate collection efficiency in the beam spot area.This calculation method is called the integral method and it was used to investigate the effects of beam parameters on collection efficiency.It was determined that collection efficiency is positively correlated with applied voltage,beam size,and beam energy,but negatively correlated with beam current intensity.Additionally,it was confirmed that collection efficiency is improved when the air filling the monitor parallel plate ionization chamber is replaced with nitrogen.The collection efficiency of monitor parallel plate ionization chambers is the main uncertainty in the beam control of pencil beam scanning systems. Existing calculation methods for collection efficiency in photon or passive scattering proton systems have not considered the characteristics of non-uniform charge density in pencil beam scanning systems. In this study, Boag’s theory was applied to a proton pencil beam scanning system. The transverse distribution of charge density in the ionization chamber was considered to be a Gaussian function and an analytical solution was derived to calculate collection efficiency in the beam spot area. This calculation method is called the integral method and it was used to investigate the effects of beam parameters on collection efficiency. It was determined that collection efficiency is positively correlated with applied voltage, beam size, and beam energy,but negatively correlated with beam current intensity.Additionally, it was confirmed that collection efficiency is improved when the air filling the monitor parallel plate ionization chamber is replaced with nitrogen.

关 键 词：Collection efficiency Monitor ionization chamber Pencil beam scanning Proton therapy 

分 类 号：R730.5[医药卫生—肿瘤]