Moradi F, Khandaker Mayeen Uddin, Alrefae T, Ramazanian H, Bradley D A
Department of Physics, University of Malaya, Kuala Lumpur, Malaysia.
Department of Physics, University of Malaya, Kuala Lumpur, Malaysia; Centre for Biomedical Physics, School of Healthcare and Medical Sciences, Sunway University, 47500, Bandar Sunway, Selangor, Malaysia.
Appl Radiat Isot. 2019 Apr;146:120-126. doi: 10.1016/j.apradiso.2019.01.031. Epub 2019 Feb 1.
Studies of radiation interactions with tissue equivalent material find importance in efforts that seek to avoid unjustifiable dose to patients, also in ensuring quality control of for instance nuclear medicine imaging equipment. Use of the Monte Carlo (MC) simulation tool in such characterization processes allows for the avoidance of costly experiments involving transmitted X- and γ-ray spectrometry. Present work investigates MC simulations of γ-ray transmission through tissue equivalent solid phantoms. Use has been made of a range of radionuclide gamma ray sources, Tc, I, Cs, Co (offering photons in the energy range from a few keV up to low MeV), popularly applied in medicine and in some cases for gauging in industry, obtaining the transmission spectra following their interaction with various phantom materials and thicknesses. In validation of the model, the simulated values of mass attenuation coefficients (μ/ρ) for different phantom materials and thicknesses were found to be in good agreement with reference values (NIST, 2004) to within 1.1% for all material compositions. For all of the primary photon energies and medium thicknesses of interest herein, results show that multiple scattering peaks are generally located at energies lower than 100 keV, although for the larger phantom thicknesses it is more difficult to distinguish single, double and multiple scattering in the gamma spectra. Transmitted photon spectra investigated for water, soft tissue, breast, brain and lung tissue slab phantoms are demonstrated to be practically independent of the phantom material, while a significant difference is observed for the spectra transmitted through bone that was proved to be due to the density effect and not material composition.
对辐射与组织等效材料相互作用的研究，在旨在避免对患者造成不合理剂量的工作中具有重要意义，在确保例如核医学成像设备的质量控制方面也很重要。在此类表征过程中使用蒙特卡罗（MC）模拟工具，可以避免涉及透射X射线和γ射线光谱测定的昂贵实验。当前工作研究了γ射线透过组织等效固体模体的MC模拟。使用了一系列放射性核素γ射线源，如锝、碘、铯、钴（提供能量范围从几keV到低MeV的光子），这些在医学中广泛应用，在某些情况下也用于工业测量，获取它们与各种模体材料和厚度相互作用后的透射光谱。在模型验证中，发现不同模体材料和厚度的质量衰减系数（μ/ρ）模拟值与参考值（美国国家标准与技术研究院，2004年）在所有材料成分上的偏差均在1.1%以内，吻合良好。对于本文所关注的所有初级光子能量和中等厚度，结果表明，多重散射峰通常位于低于100 keV的能量处，不过对于较大的模体厚度，在γ光谱中更难区分单次、二次和多重散射。研究表明，水、软组织、乳腺、脑和肺组织平板模体的透射光子光谱实际上与模体材料无关，而透过骨的光谱则存在显著差异，事实证明这是由密度效应而非材料成分导致的。
