Papadimitroulas Panagiotis, Erwin William D, Iliadou Vasiliki, Kostou Theodora, Loudos George, Kagadis George C
R&D Department, BET Solutions, 116 Alexandras Ave., Athens, GR-11472, Greece.
Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Med Phys. 2018 Jun 19. doi: 10.1002/mp.13055.
Herein, we introduce a methodology for estimating the absorbed dose in organs at risk that is based on specified clinically derived radiopharmaceutical biodistributions and personalized anatomical characteristics.
To evaluate the proposed methodology, we used realistic Monte Carlo (MC) simulations and computational pediatric models to calculate a parameter called in this work the "specific absorbed dose rate" (SADR). The SADR is a unique quantitative metric in that it is specific to a particular organ. It is defined as the absorbed dose rate in an organ when the biodistribution of radioactivity over the whole body is considered. Initially, we applied a validation procedure that calculated specific absorbed fractions (SAFs) from mono-energetic photon sources in the range of 10 keV-2 MeV and compared them with previously published data. We calculated the SADRs for five different radiopharmaceuticals ( Tc-MDP, I-mIBG, I-MIBG, I-NaI, and Sm-EDTMP) based on their biodistributions at four or five different times; the biodistributions were derived from the clinical scintigraphic data of pediatric patients. We used six models representing male and female patients aged 5, 8, and 14 yr to investigate the absorbed dose variability due to anatomical variations. The GATE Monte Carlo toolkit was used to calculate absorbed doses per organ. Finally, we compared the SADR methodology to that of OLINDA/EXM 1.1 using rescaled masses according to the studied models. Four target organs were considered for calculating the absorbed doses.
The ratios of SAFs calculated with GATE simulations to those based on previously published data were between 0.9 and 2.2 when the liver was used as a source organ. Subsequently, we used GATE to calculate a dataset of SADRs for the six pediatric models. The SADRs for pediatric models whose total body weights ranged from 20 to 40 kg varied up to approximately 90%, whereas those for models of similar body masses varied less than 15%. Finally, we found absorbed dose discrepancies of approximately 10-150% between the SADR methodology and OLINDA for two different radiopharmaceuticals. Absorbed doses from SADRs and from individualized S-values in the same pediatric model differed approximately 1-50%.
Because pediatric radiopharmaceutical dosimetric estimates demonstrate large variation due to the patient's anatomical characteristics, personalized data should be considered. Using our SADR method in a larger population of phantoms and for a variety of radiopharmaceuticals could enhance the personalization of dosimetry in pediatric nuclear medicine. The proposed methodology provides the advantage of creating time-dependent organ dose rate curves.
在此，我们介绍一种基于特定临床得出的放射性药物生物分布和个性化解剖特征来估算危险器官吸收剂量的方法。
为评估所提出的方法，我们使用逼真的蒙特卡罗（MC）模拟和计算儿科模型来计算在本研究中称为“比吸收剂量率”（SADR）的参数。SADR是一种独特的定量指标，因为它特定于某个特定器官。它被定义为在考虑全身放射性生物分布时器官中的吸收剂量率。最初，我们应用了一种验证程序，该程序从10 keV - 2 MeV范围内的单能光子源计算比吸收分数（SAF），并将其与先前发表的数据进行比较。我们根据五种不同放射性药物（锝 - 亚甲基二膦酸盐（Tc - MDP）、碘 - 间碘苄胍（I - mIBG）、碘 - 间碘苄胍（I - MIBG）、碘 - 碘化钠（I - NaI）和钐 - 乙二胺四甲基膦酸（Sm - EDTMP））在四个或五个不同时间的生物分布计算了SADR；这些生物分布来自儿科患者的临床闪烁扫描数据。我们使用六个代表5岁、8岁和14岁男性和女性患者的模型来研究由于解剖变异导致的吸收剂量变异性。使用GATE蒙特卡罗工具包计算每个器官的吸收剂量。最后，我们根据所研究的模型使用重新缩放的质量，将SADR方法与OLINDA/EXM 1.1的方法进行比较。计算吸收剂量时考虑了四个靶器官。
当将肝脏用作源器官时，用GATE模拟计算的SAF与基于先前发表数据的SAF之比在0.9至2.2之间。随后，我们使用GATE为六个儿科模型计算了SADR数据集。全身重量范围为20至40 kg的儿科模型的SADR变化高达约90%，而体重相似的模型的SADR变化小于15%。最后，我们发现两种不同放射性药物的SADR方法与OLINDA之间的吸收剂量差异约为10 - 150%。同一儿科模型中SADR和个体化S值的吸收剂量相差约1 - 50%。
由于儿科放射性药物剂量学估计因患者的解剖特征而显示出很大差异，应考虑个性化数据。在更多的体模群体中并针对多种放射性药物使用我们的SADR方法可以增强儿科核医学剂量学的个性化。所提出的方法具有创建随时间变化的器官剂量率曲线的优势。
