Targeted radionuclide therapy (TRT) is gaining importance. For TRT to be also used as adjuvant therapy or for treating minimal residual disease, there is a need to increase the radiation dose to small tumours. The aim of this in silico study was to compare the performances of 161Tb (a medium-energy β− emitter with additional Auger and conversion electron emissions) and 177Lu for irradiating single tumour cells and micrometastases, with various distributions of the radionuclide. We used the Monte Carlo track-structure (MCTS) code CELLDOSE to compute the radiation doses delivered by 161Tb and 177Lu to single cells (14 μm cell diameter with 10 μm nucleus diameter) and to a tumour cluster consisting of a central cell surrounded by two layers of cells (18 neighbours). We focused the analysis on the absorbed dose to the nucleus of the single tumoral cell and to the nuclei of the cells in the cluster. For both radionuclides, the simulations were run assuming that 1 MeV was released per μm3 (1436 MeV/cell). We considered various distributions of the radionuclides: either at the cell surface, intracytoplasmic or intranuclear. For the single cell, the dose to the nucleus was substantially higher with 161Tb compared to 177Lu, regardless of the radionuclide distribution: 5.0 Gy vs. 1.9 Gy in the case of cell surface distribution; 8.3 Gy vs. 3.0 Gy for intracytoplasmic distribution; and 38.6 Gy vs. 10.7 Gy for intranuclear location. With the addition of the neighbouring cells, the radiation doses increased, but remained consistently higher for 161Tb compared to 177Lu. For example, the dose to the nucleus of the central cell of the cluster was 15.1 Gy for 161Tb and 7.2 Gy for 177Lu in the case of cell surface distribution of the radionuclide, 17.9 Gy for 161Tb and 8.3 Gy for 177Lu for intracytoplasmic distribution and 47.8 Gy for 161Tb and 15.7 Gy for 177Lu in the case of intranuclear location. 161Tb should be a better candidate than 177Lu for irradiating single tumour cells and micrometastases, regardless of the radionuclide distribution.

中文翻译：

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单个肿瘤细胞和微转移的放射剂量为161Tb和177Lu。

靶向放射性核素治疗（TRT）越来越重要。为了将TRT也用作辅助疗法或用于治疗最小的残留疾病，需要增加对小肿瘤的放射剂量。这项计算机模拟研究的目的是比较161Tb（具有额外的俄歇和转换电子发射的中能β-发射体）和177Lu照射单个肿瘤细胞和微转移以及各种放射性核素的性能。我们使用蒙特卡洛轨道结构（MCTS）代码CELLDOSE计算161Tb和177Lu对单细胞（细胞直径14μm，核直径10μm）和由两个中心包围的中心细胞组成的肿瘤簇的辐射剂量层细胞（18个邻居）。我们将分析的重点放在单个肿瘤细胞核和簇中细胞核的吸收剂量上。对于这两种放射性核素，假设每μm3释放1 MeV（1436 MeV /细胞），进行模拟。我们考虑了放射性核素的各种分布：在细胞表面，胞质内或核内。对于单细胞，无论放射性核素的分布如何，与177Lu相比，使用161Tb的细胞核剂量要高得多：在细胞表面分布的情况下为5.0 Gy对1.9 Gy。细胞质内分布为8.3 Gy与3.0 Gy；核内定位为38.6 Gy与10.7 Gy。随着邻近细胞的增加，辐射剂量增加，但与177Lu相比，161Tb始终保持较高。例如，在放射性核素的细胞表面分布情况下，簇中心细胞核的剂量分别为：161Tb为15.1 Gy，177Lu为7.2 Gy，161Tb为17.9 Gy，胞浆内分布为177Lu 8.3 Gy，161Tb为47.8 Gy在核内定位的情况下，177Lu的光通量为15.7 Gy。不管放射性核素的分布如何，对于放射单个肿瘤细胞和微转移，161Tb应该比177Lu更好。