Champion Christophe, Quinto Michele A, Morgat Clément, Zanotti-Fregonara Paolo, Hindié Elif
1. Université de Bordeaux, CNRS/IN2P3, Centre d'Etudes Nucléaires de Bordeaux Gradignan (CENBG), France;
2. Service de Médecine Nucléaire - CHU de Bordeaux; UMR-CNRS 5287; LabEx TRAIL; Université de Bordeaux, FRANCE.
Theranostics. 2016 Jun 18;6(10):1611-8. doi: 10.7150/thno.15132. eCollection 2016.
Radionuclide therapy is increasingly seen as a promising option to target minimal residual disease. Copper-67, scandium-47 and terbium-161 have a medium-energy β(-) emission which is similar to that of lutetium-177, but offer the advantage of having diagnostic partner isotopes suitable for pretreatment imaging. The aim of this study was to compare the efficacy of (67)Cu, (47)Sc and (161)Tb to irradiate small tumors.
The absorbed dose deriving from a homogeneous distribution of (67)Cu, (47)Sc or (161)Tb in water-density spheres was calculated with the Monte Carlo code CELLDOSE. The diameters of the spheres ranged from 5 mm to 10 µm, thus simulating micrometastases or single tumor cells. All electron emissions, including β(-) spectra, Auger and conversion electrons were taken into account. Because these radionuclides differ in electron energy per decay, the simulations were run assuming that 1 MeV was released per µm(3), which would result in a dose of 160 Gy if totally absorbed.
The absorbed dose was similar for the three radionuclides in the 5-mm sphere (146-149 Gy), but decreased differently in smaller spheres. In particular, (161)Tb delivered higher doses compared to the other radionuclides. For instance, in the 100-µm sphere, the absorbed dose was 24.1 Gy with (67)Cu, 14.8 Gy with (47)Sc and 44.5 Gy with (161)Tb. Auger and conversion electrons accounted for 71% of (161)Tb dose. The largest dose differences were found in cell-sized spheres. In the 10-µm sphere, the dose delivered by (161)Tb was 4.1 times higher than that from (67)Cu and 8.1 times that from (47)Sc.
(161)Tb can effectively irradiate small tumors thanks to its decay spectrum that combines medium-energy β(-) emission and low-energy conversion and Auger electrons. Therefore (161)Tb might be a better candidate than (67)Cu and (47)Sc for treating minimal residual disease in a clinical setting.
放射性核素治疗越来越被视为一种针对微小残留病灶的有前景的选择。铜 - 67、钪 - 47和铽 - 161具有中等能量的β(-)发射，这与镥 - 177类似，但具有适合预处理成像的诊断性伴生同位素这一优势。本研究的目的是比较(67)Cu、(47)Sc和(161)Tb对小肿瘤的辐照效果。
使用蒙特卡罗代码CELLDOSE计算水密度球体中(67)Cu、(47)Sc或(161)Tb均匀分布产生的吸收剂量。球体直径范围从5毫米到10微米，从而模拟微转移灶或单个肿瘤细胞。考虑了所有电子发射，包括β(-)能谱、俄歇电子和内转换电子。由于这些放射性核素每次衰变的电子能量不同，模拟运行时假设每立方微米释放1兆电子伏能量，若完全吸收则剂量为160戈瑞。
对于5毫米球体，三种放射性核素的吸收剂量相似（146 - 149戈瑞），但在较小球体中剂量下降情况不同。特别是，与其他放射性核素相比，(161)Tb能提供更高剂量。例如，在100微米球体中，(67)Cu的吸收剂量为24.1戈瑞，(47)Sc为14.8戈瑞，(161)Tb为44.5戈瑞。俄歇电子和内转换电子占(161)Tb剂量的71%。在细胞大小的球体中发现最大剂量差异。在10微米球体中，(161)Tb的剂量比(67)Cu高4.1倍，比(47)Sc高8.1倍。
(161)Tb因其衰变谱结合了中等能量的β(-)发射以及低能量的内转换电子和俄歇电子，能够有效地辐照小肿瘤。因此，在临床环境中，(161)Tb可能比(67)Cu和(47)Sc更适合治疗微小残留病灶。
