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Determinations of the Correction Factors for Small Fields in Cylindrical Ionization Chambers Based on Measurement and Numerical Calculation

Authors
 Kwangwoo Park  ;  Wonhoon Choi  ;  Sungho Park  ;  Jin Hwa Choi  ;  Suk Won Park  ;  Jino Bak 
Citation
 JOURNAL OF THE KOREAN PHYSICAL SOCIETY, Vol.67(1) : 57-62, 2015 
Journal Title
 JOURNAL OF THE KOREAN PHYSICAL SOCIETY 
ISSN
 0374-4884 
Issue Date
2015
Keywords
Small field ; Correction factor ; Output factor ; Dosimetry
Abstract
We investigated the volume averaging effect for air-filled cylindrical ionization chambers to determine the correction factors in a small photon field for a given chamber. We measured output factors with several cylindrical ionization chambers, and by using a mathematical method similar to deconvolution, we modeled the non-constant and inhomogeneous exposure function in the cavity of the chamber. The parameters in the exposure function and the correction factors were determined by solving a system of equations that we had developed by using the measured data and the geometry of the given chamber. The correction factors (CFs) were very similar to those obtained from Monte Carlo (MC) simulations. For example, the CFs in this study were found to be 1.116 for PTW31010 and 1.0225 for PTW31016 while the CFs obtained from MC simulations were reported as being approximately between 1.17 and 1.20 for PTW31010 and between 1.02 and 1.06 for PTW31016 in a 6-MV photon beam of 1 × 1 cm2. Furthermore, the method of deconvolution combined with the MC result for the chamber’s response function showed a similar CF for PTW 30013, which was reported as 2.29 and 1.54 for a 1 × 1 cm2 and a 1.5 × 1.5 cm2 field size, respectively. The CFs from our method were similar, 2.42 and 1.54. In addition, we report CFs for PTW30013, PTW31010, PTW31016, IBA FC23-C, and IBA CC13. As a consequence, we suggest the use of our method to measure the correct output factor by using the fact that an inhomogeneous exposure causes a volume averaging effect in the cavity of air-filled cylindrical ionization chamber. The result obtained by using our method is very similar to that obtained from MC simulations. The method we developed can easily be applied in clinics.
Full Text
https://link.springer.com/article/10.3938/jkps.67.57
DOI
2015
Appears in Collections:
1. College of Medicine (의과대학) > Dept. of Radiation Oncology (방사선종양학교실) > 1. Journal Papers
Yonsei Authors
Park, Kwang Woo(박광우) ORCID logo https://orcid.org/0000-0002-9843-7985
Choi, Won Hoon(최원훈)
URI
https://ir.ymlib.yonsei.ac.kr/handle/22282913/157126
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