Kramer R, Khoury H J, Vieira J W
Departamento de Energia Nuclear, Universidade Federal de Pernambuco, Av. Prof. Luiz Freire 1000, Cidade Universitária, CEP: 50740-540, Recife, PE, Brazil.
Phys Med Biol. 2005 Nov 7;50(21):5105-26. doi: 10.1088/0031-9155/50/21/011. Epub 2005 Oct 19.
For the last two decades, the organ and tissue equivalent dose as well as effective dose conversion coefficients recommended by the International Commission on Radiological Protection (ICRP) have been determined with exposure models based on stylized MIRD5-type phantoms representing the human body with its radiosensitive organs and tissues according to the ICRP Reference Man released in Publication No. 23, on Monte Carlo codes sometimes simulating rather simplified radiation physics and on tissue compositions from different sources. Meanwhile the International Commission on Radiation Units and Measurements (ICRU) has published reference data for human tissue compositions in Publication No. 44, and the ICRP has released a new report on anatomical reference data in Publication No. 89. As a consequence many of the components of the traditional stylized exposure models used to determine the effective dose in the past have to be replaced: Monte Carlo codes, human phantoms and tissue compositions. This paper presents results of comprehensive investigations on the dosimetric consequences to be expected from the replacement of the traditional stylized exposure models by the voxel-based exposure models. Calculations have been performed with the EGS4 Monte Carlo code for external and internal exposures to photons and electrons with the stylized, gender-specific MIRD5-type phantoms ADAM and EVA on the one hand and with the recently developed tomographic or voxel-based phantoms MAX and FAX on the other hand for a variety of exposure conditions. Ratios of effective doses for the voxel-based and the stylized exposure models will be presented for external and internal exposures to photons and electrons as a function of the energy and the geometry of the radiation field. The data indicate that for the exposure conditions considered in these investigations the effective dose may change between +60% and -50% after the replacement of the traditional exposure models by the voxel-based exposure models.
在过去二十年中，国际放射防护委员会（ICRP）推荐的器官和组织当量剂量以及有效剂量转换系数，是根据第23号出版物中发布的ICRP参考人，使用基于风格化MIRD5型体模的暴露模型来确定的，这些体模代表了人体及其放射敏感器官和组织，同时还基于有时模拟相当简化的辐射物理学的蒙特卡罗代码以及来自不同来源的组织成分。与此同时，国际辐射单位与测量委员会（ICRU）在第44号出版物中公布了人体组织成分的参考数据，ICRP在第89号出版物中发布了一份关于解剖学参考数据的新报告。因此，过去用于确定有效剂量的传统风格化暴露模型的许多组成部分都必须更换：蒙特卡罗代码、人体体模和组织成分。本文介绍了关于用基于体素的暴露模型取代传统风格化暴露模型所预期的剂量学后果的综合研究结果。一方面使用EGS4蒙特卡罗代码，针对光子和电子的外部和内部暴露，分别使用风格化的、按性别区分的MIRD5型体模ADAM和EVA进行计算；另一方面针对各种暴露条件，使用最近开发的断层扫描或基于体素的体模MAX和FAX进行计算。将给出基于体素的暴露模型和风格化暴露模型对于光子和电子的外部和内部暴露的有效剂量比，作为辐射场能量和几何形状的函数。数据表明，对于这些研究中考虑的暴露条件，用基于体素的暴露模型取代传统暴露模型后，有效剂量可能在+60%至 -50%之间变化。
