Pistone Daniele, Amato Ernesto, Auditore Lucrezia, Baldari Sergio, Italiano Antonio
Department of Biomedical and Dental Sciences and of Morphologic and Functional Imaging (BIOMORF), University of Messina, Messina, Italy; INFN, National Institute for Nuclear Physics, Section of Catania, Catania, Italy.
Department of Biomedical and Dental Sciences and of Morphologic and Functional Imaging (BIOMORF), University of Messina, Messina, Italy; INFN, National Institute for Nuclear Physics, Section of Catania, Catania, Italy; Health Physics Unit, University Hospital "Gaetano Martino", Messina, Italy.
Phys Med. 2023 Aug;112:102624. doi: 10.1016/j.ejmp.2023.102624. Epub 2023 Jun 22.
Internal Bremsstrahlung (IB) is a process accompanying β-decay but neglected in Voxel S-Values (VSVs) calculation. Aims of this work were to calculate, through Monte Carlo (MC) simulation, updated Y-VSVs including IB, and to develop an analytical model to evaluate Y-VSVs for any voxel size of practical interest.
GATE (Geant4 Application for Tomographic Emission) was employed for simulating voxelized geometries of soft tissue, with voxels sides l ranging from 2 to 6 mm, in steps of 0.5 mm. The central voxel was set as a homogeneous source of Y when IB photons are not modelled. For each l, the VSVs were computed for Y decays alone and for Y + IB. The analytical model was then built through fitting procedures of the VSVs including IB contribution.
Comparing GATE-VSVs with and without IB, differences between + 25% and + 30% were found for distances from the central voxel larger than the maximum β-range. The analytical model showed an agreement with MC simulations within ± 5% in the central voxel and in the Bremsstrahlung tails, for any l value examined, and relative differences lower than ± 40%, for other distances from the source.
The presented Y-VSVs include for the first time the contribution due to IB, thus providing a more accurate set of dosimetric factors for three-dimensional internal dosimetry of Y-labelled radiopharmaceuticals and medical devices. Furthermore, the analytical model constitutes an easy and fast alternative approach for Y-VSVs estimation for non-standard voxel dimensions.
内韧致辐射（IB）是伴随β衰变的一个过程，但在体素S值（VSV）计算中被忽略。本研究的目的是通过蒙特卡罗（MC）模拟计算包含IB的更新后的Y-VSV，并开发一个分析模型来评估任何实际感兴趣的体素大小的Y-VSV。
使用GATE（用于断层发射的Geant4应用程序）模拟软组织的体素化几何结构，体素边长l范围为2至6毫米，步长为0.5毫米。当不模拟IB光子时，将中心体素设置为Y的均匀源。对于每个l，分别计算仅Y衰变以及Y + IB时的VSV。然后通过对包含IB贡献的VSV进行拟合程序来建立分析模型。
比较有和没有IB时的GATE-VSV，对于距离中心体素大于最大β范围的情况，发现差异在+25%至+30%之间。分析模型显示，在所研究的任何l值下，在中心体素和韧致辐射尾部与MC模拟的一致性在±5%以内，对于离源的其他距离，相对差异低于±40%。
所呈现的Y-VSV首次包含了IB的贡献，从而为Y标记的放射性药物和医疗设备的三维内照射剂量学提供了一组更准确的剂量学因子。此外，分析模型为非标准体素尺寸的Y-VSV估计提供了一种简单快速的替代方法。
