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. 2024 Jul 15;11(1):61.
doi: 10.1186/s40658-024-00669-5.

Comparison of the dosimetry of scandium-43 and scandium-44 patient organ doses in relation to commonly used gallium-68 for imaging neuroendocrine tumours

Carlos Vinícius Gomes  1   2 , Bruno Melo Mendes  3 , Lucas Paixão  4 , Silvano Gnesin  5 , Cristina Müller  6 , Nicholas P van der Meulen  6   7 , Klaus Strobel  8 , Telma Cristina Ferreira Fonseca  9   3 , Thiago Viana Miranda Lima  8   10
Affiliations

Comparison of the dosimetry of scandium-43 and scandium-44 patient organ doses in relation to commonly used gallium-68 for imaging neuroendocrine tumours

Carlos Vinícius Gomes et al. EJNMMI Phys. .

Abstract

Background: 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.

Methods: Absorbed dose per injected activity (AD/IA) from the generated time-integrated activity curve (TIAC) were estimated using the radiopeptides [43/44/44mSc]Sc- and [68Ga]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.

Results: 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 [43/44Sc]Sc-DOTATATE compared to its 68Ga-based counterpart.

Conclusion: This study found that [43/44Sc]Sc-DOTATATE delivers a higher absorbed dose to organs at risk compared to [68Ga]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.

Keywords: Dosimetry; Monte Carlo; Neuroendocrine tumours; PET; Radiopeptides; Scandium.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Computational phantoms of the reference ICRP 110: female (AF), left, and male (AM), right
Fig. 2
Fig. 2
Absorbed dose per injected activity estimated from the mean MC codes and Olinda/EXM software by radionuclide. The results are represented for the female (AF) and male (AM) ICRP reference phantoms
Fig. 3
Fig. 3
Organ dose comparison for both male and female phantoms for the different radioisotopes
Fig. 4
Fig. 4
Effective dose comparison for the different scandium radioisotopes. Effect on scandium concentrations in the mixture between scandium-43, scandium-44, and scandium-44m
See this image and copyright information in PMC

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