Nogueira P, Rühm W
Thünen Institute of Fisheries Ecology, Herwigstraße 31, 27572 Bremerhaven, Germany.
Helmholtz Zentrum München - German Research Center for Environmental Health, Institute of Radiation Medicine, Ingolstädter Landstraße 1, D-85764 Neuherberg, Germany.
J Radiol Prot. 2020 Nov 11;40(4). doi: 10.1088/1361-6498/abbe36.
Incorporation of bone seeking alpha-emitting radionuclides such asAm are of special concern, due to the potential of alpha particles to damage the extremely radiation-sensitive bone marrow. In the case of an internal contamination withAm, directmeasurements using Gamma-detectors are typically used to quantify the incorporated activity. Such detectors need to be calibrated with an anatomical phantom, for example of the skull, of knownAm activity that reproduces the anatomy of the measured individual as closely as possible. Any difference in anatomy and material composition between phantom and individual will bias the estimation of the incorporated activity. Consequently, in this work the impact of the most important anatomical parameters on detection efficiency of one of the germanium detectors of the Helmholtz Center Munich (HMGU) partial body counter were systematically studied. For that a detailed model of the germanium detector was implemented in the Monte Carlo codes GEANT4 and MCNPX. To simulate the detector efficiency, various skull voxel phantoms were used. By changing the phantom dimensions and geometry the impact of parameters such as shape and size of the skull, thickness of tissue covering the skull bone, distribution ofAm across the scull and within the skull bone matrix, on the detector efficiency was studied. Approaches to correct for these parameters were specifically developed for three physical skull phantoms for which Voxel phantoms were available: Case 102 USTUR phantom, Max-06 phantom, BfS phantom. Based on the impact of each parameter, correction factors for an 'individual-specific' calibration were calculated and applied to a realAm contamination case reported in 2014. It was found that the incorporatedAm activity measured with the HMGU partial body counter was about twice as large as that estimated when using the BfS skull phantom without applying any correction factor for person-specific parameters. It is concluded that the approach developed in the present study should in the future be applied routinely for skull phantom measurements, because it allows for a considerably improved reconstruction of incorporatedAm using partial body counters.
由于发射α粒子的亲骨性放射性核素（如镅）有损害极其辐射敏感的骨髓的可能性，因此对其掺入情况格外关注。在发生镅的体内污染时，通常使用伽马探测器进行直接测量以量化掺入活度。此类探测器需要用解剖体模（例如已知镅活度的头骨体模）进行校准，该体模要尽可能精确地再现被测个体的解剖结构。体模与个体之间在解剖结构和材料组成上的任何差异都会使掺入活度的估计产生偏差。因此，在本研究中，系统地研究了最重要的解剖学参数对慕尼黑亥姆霍兹中心（HMGU）局部身体计数器的一个锗探测器探测效率的影响。为此，在蒙特卡罗代码GEANT4和MCNPX中实现了锗探测器的详细模型。为模拟探测器效率，使用了各种头骨体素体模。通过改变体模尺寸和几何形状，研究了诸如头骨的形状和大小、覆盖头骨的组织厚度、镅在座骨和头骨骨基质内的分布等参数对探测器效率的影响。针对有体素体模可用的三种物理头骨体模，专门开发了校正这些参数的方法：案例102 USTUR体模、Max - 06体模、BfS体模。基于每个参数的影响，计算了“个体特异性”校准的校正因子，并将其应用于2014年报告的一个实际镅污染案例。结果发现，使用HMGU局部身体计数器测量的掺入镅活度约为在不应用任何个体特异性参数校正因子的情况下使用BfS头骨体模估计值的两倍。得出的结论是，本研究中开发的方法今后应常规应用于头骨体模测量，因为它能够显著改进使用局部身体计数器对掺入镅的重建。
