Department of Nuclear Medicine, Beaujon Hospital, Assistance Publique-Hôpitaux de Paris, Clichy, France.
J Nucl Med. 2010 Oct;51(10):1600-7. doi: 10.2967/jnumed.110.077149. Epub 2010 Sep 16.
This article presents a revised voxel S values (VSVs) approach for dosimetry in targeted radiotherapy, allowing dose calculation for any voxel size and shape of a given SPECT or PET dataset. This approach represents an update to the methodology presented in MIRD pamphlet no. 17.
VSVs were generated in soft tissue with a fine spatial sampling using the Monte Carlo (MC) code MCNPX for particle emissions of 9 radionuclides: (18)F, (90)Y, (99m)Tc, (111)In, (123)I, (131)I, (177)Lu, (186)Re, and (201)Tl. A specific resampling algorithm was developed to compute VSVs for desired voxel dimensions. The dose calculation was performed by convolution via a fast Hartley transform. The fine VSVs were calculated for cubic voxels of 0.5 mm for electrons and 1.0 mm for photons. Validation studies were done for (90)Y and (131)I VSV sets by comparing the revised VSV approach to direct MC simulations. The first comparison included 20 spheres with different voxel sizes (3.8-7.7 mm) and radii (4-64 voxels) and the second comparison a hepatic tumor with cubic voxels of 3.8 mm. MC simulations were done with MCNPX for both. The third comparison was performed on 2 clinical patients with the 3D-RD (3-Dimensional Radiobiologic Dosimetry) software using the EGSnrc (Electron Gamma Shower National Research Council Canada)-based MC implementation, assuming a homogeneous tissue-density distribution.
For the sphere model study, the mean relative difference in the average absorbed dose was 0.20% ± 0.41% for (90)Y and -0.36% ± 0.51% for (131)I (n = 20). For the hepatic tumor, the difference in the average absorbed dose to tumor was 0.33% for (90)Y and -0.61% for (131)I and the difference in average absorbed dose to the liver was 0.25% for (90)Y and -1.35% for (131)I. The comparison with the 3D-RD software showed an average voxel-to-voxel dose ratio between 0.991 and 0.996. The calculation time was below 10 s with the VSV approach and 50 and 15 h with 3D-RD for the 2 clinical patients.
This new VSV approach enables the calculation of absorbed dose based on a SPECT or PET cumulated activity map, with good agreement with direct MC methods, in a faster and more clinically compatible manner.
本文提出了一种改进的体素 S 值（VSV）方法，用于靶向放射治疗中的剂量计算，允许对任何给定 SPECT 或 PET 数据集的体素大小和形状进行剂量计算。该方法是对 MIRD 小册子第 17 号中介绍的方法的更新。
使用蒙特卡罗（MC）代码 MCNPX 对 9 种放射性核素（18）F、（90）Y、（99m）Tc、（111）In、（123）I、（131）I、（177）Lu、（186）Re 和（201）Tl 的粒子发射进行软组织中的精细空间采样，生成 VSVs。开发了一种特定的重采样算法，用于计算所需体素尺寸的 VSVs。通过快速哈特利变换的卷积进行剂量计算。为电子的立方体素 0.5mm 和光子的 1.0mm 计算精细 VSVs。通过将修订后的 VSV 方法与直接 MC 模拟进行比较，对（90）Y 和（131）I VSV 集进行了验证研究。第一次比较包括 20 个具有不同体素大小（3.8-7.7mm）和半径（4-64 个体素）的球体，第二次比较包括一个具有 3.8mm 立方体素的肝肿瘤。两种情况均使用 MCNPX 进行 MC 模拟。第三次比较是在使用基于 EGSnrc（加拿大国家研究委员会电子伽马淋浴）的 MC 实现的 3D-RD（3 维放射生物学剂量学）软件上对 2 名临床患者进行的，假设组织密度分布均匀。
对于球体模型研究，（90）Y 的平均吸收剂量的平均相对差异为 0.20%±0.41%，（131）I 的平均相对差异为-0.36%±0.51%（n=20）。对于肝肿瘤，（90）Y 的肿瘤平均吸收剂量差异为 0.33%，（131）I 的差异为-0.61%，（90）Y 的肝脏平均吸收剂量差异为 0.25%，（131）I 的差异为-1.35%。与 3D-RD 软件的比较显示平均体素-体素剂量比在 0.991 和 0.996 之间。使用 VSV 方法的计算时间低于 10s，而对于 2 名临床患者，使用 3D-RD 的计算时间分别为 50h 和 15h。
这种新的 VSV 方法能够基于 SPECT 或 PET 累积活性图计算吸收剂量，与直接 MC 方法具有良好的一致性，并且计算速度更快，更符合临床要求。
