Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville, MD 20850, United States of America.
Phys Med Biol. 2019 Apr 4;64(7):075018. doi: 10.1088/1361-6560/ab0917.
Recently, the International Commission on Radiological Protection (ICRP) developed new mesh-type reference computational phantoms (MRCPs) that provide high deformability compared with the current voxel-type reference computational phantoms of ICRP Publication 110. Taking advantage of this deformability, in the present study, the MRCPs were deformed to five non-standing postures (i.e. walking, sitting, bending, kneeling, and squatting) by developing and using a systematic posture-change method based on the as-rigid-as-possible (ARAP) shape-deformation algorithm and motion-capture technology. The non-standing MRCPs were then implemented in the Geant4 Monte Carlo code to calculate a comprehensive dataset of dose coefficients (DCs) for photon external exposures. These include the dose coefficients for 29 individual organs/tissues and the dose coefficients for effective doses from 0.01 MeV to 10 GeV in the antero-posterior (AP), postero-anterior (PA), left-lateral (LLAT), right-lateral (RLAT), rotational (ROT), and isotropic (ISO) geometries. To investigate the dosimetric impact of posture, the DCs of the non-standing MRCPs were compared with those of the original MRCPs (in the standing posture). The results showed that organ/tissue doses are significantly influenced by posture, with arm position mostly influencing dose to organs/tissues in the torso region and leg position influencing dose in the pelvic region. For most cases, the gonads showed notably large differences, ranging from a few tens of percentage points to several orders of magnitude, depending on posture and irradiation geometry. The effective doses showed much smaller differences than the organ/tissue doses, but they were nonetheless significant: for example, the kneeling MRCPs in the AP geometry showed lower values at energies <10 MeV by up to 30% and greater values at higher energies by up to 40%. The presented results indicate that not only different irradiation geometries, but also different postures might be necessary in DC calculations for reliable dose estimates for radiological protection purposes.
最近，国际辐射防护委员会（ICRP）开发了新型网格型参考计算体模（MRCP），与 ICRP 出版物 110 中的当前体素型参考计算体模相比，具有更高的变形能力。利用这种变形能力，本研究通过开发和使用基于尽可能刚性（ARAP）形状变形算法和运动捕捉技术的系统姿势变换方法，将 MRCP 变形为五个非站立姿势（即行走、坐、弯、跪和蹲）。然后，将非站立 MRCP 实施到 Geant4 蒙特卡罗代码中，以计算光子外照射的综合剂量系数（DC）数据集。这些数据集包括 29 个个体器官/组织的剂量系数以及前-后（AP）、后-前（PA）、左-外侧（LLAT）、右-外侧（RLAT）、旋转（ROT）和各向同性（ISO）几何形状下从 0.01 MeV 到 10 GeV 的有效剂量系数。为了研究姿势的剂量学影响，将非站立 MRCP 的 DC 与原始 MRCP（站立姿势）的 DC 进行了比较。结果表明，器官/组织剂量受姿势影响显著，手臂位置主要影响躯干区域器官/组织的剂量，腿部位置影响骨盆区域的剂量。对于大多数情况，性腺显示出明显的差异，范围从几十到几个数量级，取决于姿势和照射几何形状。有效剂量的差异比器官/组织剂量小得多，但仍然很显著：例如，AP 几何形状下的跪姿 MRCP 在能量<10 MeV 时的剂量降低了 30%，在更高能量时的剂量增加了 40%。研究结果表明，为了进行可靠的辐射防护剂量估计，不仅需要不同的照射几何形状，还需要不同的姿势进行 DC 计算。
