Stabin M G, Konijnenberg M W
Departamento de Energia Nuclear, Universidade Federal de Pernambuco, Recife, Brazil.
J Nucl Med. 2000 Jan;41(1):149-60.
Absorbed fractions for unit density spheres in an infinite unit density medium, previously calculated for photon emitters and electron emitters, were reevaluated with the Monte Carlo codes EGS4 and MCNP4B.
Activity was assumed to be distributed uniformly throughout the spheres, and absorbed fractions for self-irradiation were calculated at discrete photon and electron energies.
For electrons, the codes were in very good agreement with each other (+/-5%) and with published values, except at higher energies in the very smallest spheres, where some differences exceeded 10%. For photons, the codes were again in good agreement with each other but produced results that varied considerably from published MIRD values. For energies <1 MeV and sphere sizes <50 g, the absorbed fractions determined using the Monte Carlo codes were typically 20%-40% higher than values in MIRD 3 and 8. For energies >1 MeV, the Monte Carlo values were sometimes lower than those in the MIRD documents. Recommended values, generally the average results from the 2 Monte Carlo codes, are given for all sphere sizes and energies for both electrons and photons.
The absorbed fractions calculated using the Monte Carlo codes should replace the older values and are helpful in evaluating tumor doses, doses to small organs, and other situations in which a uniform distribution of activity throughout a spherical structure of unit density can be assumed.
此前针对光子发射体和电子发射体计算得出的、无限单位密度介质中单位密度球体的吸收分数，使用蒙特卡罗代码EGS4和MCNP4B进行了重新评估。
假设活度在整个球体中均匀分布，并在离散的光子和电子能量下计算自辐照的吸收分数。
对于电子，除了在最小球体的较高能量处，代码之间彼此非常吻合（±5%）且与已发表的值相符，在这些较高能量处一些差异超过了10%。对于光子，代码之间再次吻合良好，但得出的结果与已发表的MIRD值有很大差异。对于能量<1 MeV且球体尺寸<50 g的情况，使用蒙特卡罗代码确定的吸收分数通常比MIRD 3和8中的值高20% - 40%。对于能量>1 MeV的情况，蒙特卡罗值有时低于MIRD文件中的值。给出了针对所有球体尺寸和能量的电子及光子的推荐值，通常是两个蒙特卡罗代码的平均结果。
使用蒙特卡罗代码计算得出的吸收分数应取代旧值，有助于评估肿瘤剂量、对小器官的剂量以及其他可假设活度在单位密度球形结构中均匀分布的情况。
