*Sunnybrook Research Institute, Toronto, Ontario, Canada; †Department of Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; †Departments of Medical Imaging and Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.
Health Phys. 2014 Jul;107(1):60-72. doi: 10.1097/HP.0000000000000051.
A primary goal of nuclear medicine facility design is to keep public and worker radiation doses As Low As Reasonably Achievable (ALARA). To estimate dose and shielding requirements, one needs to know both the dose equivalent rate constants for soft tissue and barrier transmission factors (TFs) for all radionuclides of interest. Dose equivalent rate constants are most commonly calculated using published air kerma or exposure rate constants, while transmission factors are most commonly calculated using published tenth-value layers (TVLs). Values can be calculated more accurately using the radionuclide's photon emission spectrum and the physical properties of lead, concrete, and/or tissue at these energies. These calculations may be non-trivial due to the polyenergetic nature of the radionuclides used in nuclear medicine. In this paper, the effects of dose equivalent rate constant and transmission factor on nuclear medicine dose and shielding calculations are investigated, and new values based on up-to-date nuclear data and thresholds specific to nuclear medicine are proposed. To facilitate practical use, transmission curves were fitted to the three-parameter Archer equation. Finally, the results of this work were applied to the design of a sample nuclear medicine facility and compared to doses calculated using common methods to investigate the effects of these values on dose estimates and shielding decisions. Dose equivalent rate constants generally agreed well with those derived from the literature with the exception of those from NCRP 124. Depending on the situation, Archer fit TFs could be significantly more accurate than TVL-based TFs. These results were reflected in the sample shielding problem, with unshielded dose estimates agreeing well, with the exception of those based on NCRP 124, and Archer fit TFs providing a more accurate alternative to TVL TFs and a simpler alternative to full spectral-based calculations. The data provided by this paper should assist in improving the accuracy and tractability of dose and shielding calculations for nuclear medicine facility design.
核医学设施设计的主要目标是使公众和工作人员的辐射剂量保持在合理可行尽量低（ALARA）。为了估计剂量和屏蔽要求，需要知道所有感兴趣的放射性核素的软组织剂量当量率常数和屏障传输因子（TFs）。剂量当量率常数最常用公布的空气比释动能或照射率常数计算，而传输因子最常用公布的十分之一值层（TVL）计算。可以使用放射性核素的光子发射光谱和这些能量下的铅、混凝土和/或组织的物理特性更准确地计算这些值。由于核医学中使用的放射性核素的多能性质，这些计算可能很复杂。在本文中，研究了剂量当量率常数和传输因子对核医学剂量和屏蔽计算的影响，并提出了基于最新核数据和核医学特定阈值的新值。为了便于实际使用，传输曲线拟合到三参数 Archer 方程。最后，将这项工作的结果应用于一个示例核医学设施的设计，并与使用常见方法计算的剂量进行比较，以调查这些值对剂量估算和屏蔽决策的影响。剂量当量率常数除了 NCRP 124 外，通常与文献中推导的值吻合较好。根据具体情况，Archer 拟合 TF 可以比基于 TVL 的 TF 更准确。这些结果反映在示例屏蔽问题中，除了基于 NCRP 124 的结果外，无屏蔽剂量估算值吻合较好，Archer 拟合 TF 为 TVL TF 提供了更准确的替代方案，为全谱计算提供了更简单的替代方案。本文提供的数据应有助于提高核医学设施设计中剂量和屏蔽计算的准确性和可处理性。
