Gomes Carlos Vinícius, Mendes Bruno Melo, Paixão Lucas, Gnesin Silvano, Müller Cristina, van der Meulen Nicholas P, Strobel Klaus, Fonseca Telma Cristina Ferreira, Lima Thiago Viana Miranda
Graduate School for Cellular and Biomedical Sciences, University of Bern, 3012, Bern, Switzerland.
Post-graduation Program in Nuclear Sciences and Techniques, Department of Nuclear Engineering, Federal University of Minas Gerais, Belo Horizonte, Brazil.
EJNMMI Phys. 2024 Jul 15;11(1):61. doi: 10.1186/s40658-024-00669-5.
Several research groups have explored the potential of scandium radionuclides for theragnostic applications due to their longer half-lives and equal or similar coordination chemistry between their diagnostic and therapeutic counterparts, as well as lutetium-177 and terbium-161, respectively. Unlike the gallium-68/lutetium-177 pair, which may show different in-vivo uptake patterns, the use of scandium radioisotopes promises consistent behaviour between diagnostic and therapeutic radiopeptides. An advantage of scandium's longer half-life over gallium-68 is the ability to study radiopeptide uptake over extended periods and its suitability for centralized production and distribution. However, concerns arise from scandium-44's decay characteristics and scandium-43's high production costs. This study aimed to evaluate the dosimetric implications of using scandium radioisotopes with somatostatin analogues against gallium-68 for PET imaging of neuroendocrine tumours.
Absorbed dose per injected activity (AD/IA) from the generated time-integrated activity curve (TIAC) were estimated using the radiopeptides [Sc]Sc- and [Ga]Ga-DOTATATE. The kidneys, liver, spleen, and red bone marrow (RBM) were selected for dose estimation studies. The EGSnrc and MCNP6.1 Monte Carlo (MC) codes were used with female (AF) and male (AM) ICRP phantoms. The results were compared to Olinda/EXM software, and the effective dose concentrations assessed, varying composition between the scandium radioisotopes.
Our findings showed good agreement between the MC codes, with - 3 ± 8% mean difference. Kidneys, liver, and spleen showed differences between the MC codes (min and max) in a range of - 4% to 8%. This was observed for both phantoms for all radiopeptides used in the study. Compared to Olinda/EXM the largest observed difference was for the RBM, of 21% for the AF and 16% for the AM for scandium- and gallium-based radiopeptides. Despite the differences, our findings showed a higher absorbed dose on [Sc]Sc-DOTATATE compared to its Ga-based counterpart.
This study found that [Sc]Sc-DOTATATE delivers a higher absorbed dose to organs at risk compared to [Ga]Ga-DOTATATE, assuming equal distribution. This is due to the longer half-life of scandium radioisotopes compared to gallium-68. However, calculated doses are within acceptable ranges, making scandium radioisotopes a feasible replacement for gallium-68 in PET imaging, potentially offering enhanced diagnostic potential with later timepoint imaging.
由于钪放射性核素具有较长的半衰期，且其诊断和治疗对应物之间具有相同或相似的配位化学性质，以及镥 - 177和铽 - 161分别具有类似性质，几个研究小组已经探索了钪放射性核素在诊疗应用中的潜力。与可能表现出不同体内摄取模式的镓 - 68/镥 - 177对不同，使用钪放射性同位素有望使诊断性和治疗性放射性肽表现出一致的行为。钪比镓 - 68更长的半衰期的一个优点是能够在更长时间内研究放射性肽的摄取情况，并且适合集中生产和配送。然而，钪 - 44的衰变特性和钪 - 43的高生产成本引发了人们的担忧。本研究旨在评估使用钪放射性同位素与生长抑素类似物进行神经内分泌肿瘤PET成像时，相对于镓 - 68的剂量学影响。
使用放射性肽[Sc]Sc - 和[Ga]Ga - DOTATATE，根据生成的时间积分活度曲线（TIAC）估算每注射活度的吸收剂量（AD/IA）。选择肾脏、肝脏、脾脏和红骨髓（RBM）进行剂量估算研究。使用女性（AF）和男性（AM）ICRP体模，结合EGSnrc和MCNP6.1蒙特卡罗（MC）代码。将结果与Olinda/EXM软件进行比较，并评估有效剂量浓度，钪放射性同位素之间的组成有所不同。
我们的研究结果表明，MC代码之间具有良好的一致性，平均差异为 - 3±8%。肾脏、肝脏和脾脏在MC代码之间（最小值和最大值）的差异范围为 - 4%至8%。在本研究中使用的所有放射性肽的两种体模中均观察到这种情况。与Olinda/EXM相比，观察到的最大差异出现在RBM，基于钪和镓的放射性肽在AF体模中的差异为21%，在AM体模中的差异为16%。尽管存在差异，但我们的研究结果表明，[Sc]Sc - DOTATATE相比其基于镓的对应物具有更高的吸收剂量。
本研究发现，假设分布相等，[Sc]Sc - DOTATATE相对于[Ga]Ga - DOTATATE会给危险器官带来更高的吸收剂量。这是由于钪放射性同位素的半衰期比镓 - 68更长。然而，计算出的剂量在可接受范围内，这使得钪放射性同位素成为PET成像中镓 - 68的可行替代品，有可能通过后期时间点成像提供增强的诊断潜力。
