氧化铍剂量计芯片的能量响应因子：蒙特卡罗模拟与通用腔理论研究

ENERGY RESPONSE FACTOR of BeO DOSEMETER CHIPS: A MONTE CARLO SIMULATION AND GENERAL CAVITY THEORY STUDY.

作者信息

Sarigul Neslihan, Surucu Murat, Aydogan Bulent

机构信息

Institute of Nuclear Science, Hacettepe University, Ankara, Turkey.

Department of Radiation Oncology, Loyola University Medical Center, Maywood, IL, USA.

出版信息

Radiat Prot Dosimetry. 2019 Dec 31;185(3):303-309. doi: 10.1093/rpd/ncz010.

DOI:10.1093/rpd/ncz010

PMID:30806472

Abstract

The objective of this study is to determine the energy response factors for BeO optically simulated dosemeter (OSLD) using general cavity theory and Monte Carlo (MC) simulations. A virtual phantom is constructed in EGSnrc MC program and energy response of BeO OSLDs were simulated at 5 cm depth for x-ray beams ranging from 1.25 to 25 MV and at 2 cm for beams with <250 kV including ISO 4037 narrow beam energies in a virtual water phantom. The energy response factor for a given radiation quality relative to 60Co was determined for BeO and compared to the Al2O3:C and LiF:Mg,Ti dosemeters. Burlin cavity theory calculations were done using mean photon energy (MPE) of the beam spectra, while EGSnrc software package was used to carry out MC simulation of full spectra. The cavity theory and MC methods agreed well within the 0.7%. Energy response of x-ray beams at MV range showed a maximum of 1.5% under-response. At energies higher than 150 kV (105 keV MPE) showed no significant difference while a significant under-response were observed at 100 kV (53 keV MPE) and 50 kV (29 keV MPE), ~8 and ~12%, respectively. BeO, Al2O3:C and LiF:Mg,Ti dosemeters exhibited very similar energy response at higher energies mainly in the MeV range. At 50 kV (29 keV MPE), however, BeO dosemeter under responded by a factor of 0.878, while Al2O3:C and LiF:Mg,Ti dosemeters over responded by a factor of 3.2 and 1.44, respectively. Furthermore, at low energies, BeO energy response showed dependence on photon spectra. For instance, at 100 kV, the difference was ~8, ~6 and 2% for 53, 60 and 83 keV MPE (ISO 4037N-100), respectively. Furthermore, calibration with 137Cs instead of 60Co resulted up to 1.8% differences in energy response. Both energy spectrum and calibration methods make considerable differences in energy response of OSLDs. This study concludes that BeO chips are nearly energy independent at energies higher than 100 keV MPE, while Al2O3:C dosemeters show an extremely enhanced energy-response ranging between 1.44 and 3.2 at energies between 170 and 29 keV MPE mainly due to dominance of photoelectric effect.

摘要

本研究的目的是使用通用腔理论和蒙特卡罗（MC）模拟来确定氧化铍光学模拟剂量计（OSLD）的能量响应因子。在EGSnrc MC程序中构建了一个虚拟体模，并在虚拟水模中对1.25至25 MV的X射线束在5 cm深度处以及对能量小于250 kV的射线束（包括ISO 4037窄束能量）在2 cm深度处模拟了氧化铍OSLD的能量响应。确定了氧化铍相对于60Co的给定辐射质的能量响应因子，并与Al2O3:C和LiF:Mg,Ti剂量计进行了比较。使用束谱的平均光子能量（MPE）进行伯林腔理论计算，而使用EGSnrc软件包对全谱进行MC模拟。腔理论和MC方法在0.7%的范围内吻合良好。MV范围内X射线束的能量响应显示最大有1.5%的响应不足。在高于150 kV（105 keV MPE）的能量下无显著差异，而在100 kV（53 keV MPE）和50 kV（29 keV MPE）时分别观察到约8%和12%的显著响应不足。氧化铍、Al2O3:C和LiF:Mg,Ti剂量计在较高能量下，主要是在MeV范围内，表现出非常相似的能量响应。然而，在50 kV（29 keV MPE）时，氧化铍剂量计的响应不足系数为0.878，而Al2O3:C和LiF:Mg,Ti剂量计的响应过系数分别为3.2和1.44。此外，在低能量下，氧化铍的能量响应显示出对光子谱的依赖性。例如，在1百千伏时，对于53、60和83 keV MPE（ISO 4037N - 100），差异分别约为8%、6%和2%。此外，用137Cs而不是60Co进行校准导致能量响应的差异高达1.8%。能谱和校准方法都会使OSLD的能量响应产生相当大的差异。本研究得出结论，在高于100 keV MPE的能量下，氧化铍芯片几乎与能量无关，而Al2O3:C剂量计在170至29 keV MPE的能量范围内显示出极大增强的能量响应（范围在1.44至3.2之间），这主要是由于光电效应占主导地位。