Griffin Keith, Mille Matthew, Lee Choonsik
Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville, MD 20850, United States of America.
J Radiol Prot. 2018 Jun;38(2):587-606. doi: 10.1088/1361-6498/aab126. Epub 2018 Feb 21.
The risks associated with exposure to external fields of ionising radiation are important to quantify in order to provide guidance towards public and worker protection. In Publication 116 of 2010, the International Commission on Radiological Protection (ICRP) published adult male and female fluence-to-dose coefficients (henceforth referred to as dose coefficients) for external exposures to six types of idealised neutron fields. However, ICRP 116 dose coefficients are not appropriate for applications involving children due to their smaller body weight and stature. Our current work details dose coefficient calculations for children and young adolescents using the UF-NCI pediatric hybrid phantoms at all neutron energies considered in ICRP 116 (0.001 eV to 10 GeV); those dose coefficients with energy up to 150 MeV are discussed. The hybrid UF-NCI phantoms are divided into five separate age groups: newborn, 1, 5, 10, and 15 years. For these phantoms, we calculated dose coefficients for the six idealised neutron fields for 28 organs, two bone tissues, and the overall whole body effective dose. All calculations were performed using the MCNP6 radiation transport code. To validate our methodology, we first calculated dose coefficients for the ICRP adult male and female phantoms and confirmed our ability to reproduce the values published within ICRP 116. The same methodology was then applied to calculate dose coefficients for the UF-NCI pediatric phantoms. Energy-dependent trends were observed in the neutron dose coefficients for pediatric phantoms: below 100 keV, dose increases with phantom age (a proxy for body size); however, above 100 keV, the opposite trend was observed. Comparisons between field geometries showed varying trends depending on the location of the organ within the body. Explanations for these trends are also explored within. Our results are the first comprehensive set of neutron dose coefficients derived for children and young adolescents using the newest generation of hybrid phantoms. The primary application of the pediatric neutron dose coefficients presented in this work will be for a planned effort to update the dosimetry for the Japanese atomic bomb survivors.
为了为公众和工作人员的防护提供指导，量化与暴露于外部电离辐射场相关的风险很重要。在2010年的第116号出版物中，国际放射防护委员会（ICRP）公布了成年男性和女性对于六种理想化中子场外部暴露的注量-剂量系数（以下简称剂量系数）。然而，由于儿童体重和身材较小，ICRP 116剂量系数不适用于涉及儿童的应用。我们目前的工作详细介绍了在ICRP 116所考虑的所有中子能量（0.001 eV至10 GeV）下，使用UF-NCI儿童混合体模计算儿童和青少年的剂量系数；讨论了能量高达150 MeV的那些剂量系数。UF-NCI混合体模分为五个不同的年龄组：新生儿、1岁、5岁、10岁和15岁。对于这些体模，我们计算了28个器官、两种骨组织以及全身有效剂量对于六种理想化中子场的剂量系数。所有计算均使用MCNP6辐射输运代码进行。为了验证我们的方法，我们首先计算了ICRP成年男性和女性体模的剂量系数，并确认了我们再现ICRP 116中公布值的能力。然后应用相同的方法来计算UF-NCI儿童体模的剂量系数。在儿童体模的中子剂量系数中观察到了能量相关趋势：低于100 keV时，剂量随体模年龄（身体大小的一个指标）增加；然而，高于100 keV时，观察到相反的趋势。场几何形状之间的比较显示，根据器官在体内的位置不同，趋势也不同。本文还探讨了这些趋势的解释。我们的结果是使用最新一代混合体模得出的第一套针对儿童和青少年的全面中子剂量系数。这项工作中给出的儿童中子剂量系数的主要应用将是用于一项计划中的努力，即更新日本原子弹幸存者的剂量测定。
