Dear Editors,
We read with concern the uncritical endorsement of the commercial translocator protein (TSPO) radioligand 18F-GE180 in the recent manuscript by Nikam et al. [1].
It is unclear why the potential advantages of TSPO imaging in abused children must be so tightly linked to the use of one particular radioligand among the dozens that are available [2], and especially if the radioligand in question is arguably the worst TSPO tracer to ever reach human use.
The claims made in the manuscript of Nikam et al. [1] are supported by a very selective choice of the available evidence. For example, the assertion that 18F-GE180 shows “superior brain kinetics” compared to 11C-PBR28 is followed by the citation of six unrelated rat papers, none of which compared these two ligands, but does not reference the only published comparison in humans, which clearly showed that 18F-GE180 is blocked by the blood–brain barrier, its binding potential is 20 times lower than that of 11C-PBR28, and its kinetic modeling is less reliable [3]. These are not trivial problems. How would we know, for example, that children with neuropsychiatric symptoms have a negative brain scan [4] because they really do not have brain inflammation or because 18F-GE180 cannot cross the blood–brain barrier? Detailed technical descriptions of the shortcomings that make 18F-GE180 unsuitable for human use can be found in [5, 6].
Another example is the misleading assertion that 18F-GE180 has demonstrated clinical utility in patients with stroke. Instead, 18F-GE180 is the only TSPO tracer to have been discontinued for ethical reasons because of its poor imaging qualities, in an already-funded clinical trial in patients with stroke [7]. Not even this reference is cited in the manuscript by Nikam et al. [1].
These assertions lay the groundwork for using 18F-GE180 in vulnerable victims of child abuse.
In addition, no mention is made of the invasiveness of TSPO imaging. Except for select and previously validated clinical conditions, and child abuse is not among them, quantification of TSPO ligands requires arterial catheterization and blood drawing [8].
Furthermore, the dosimetry of 18F-tracers, such as 18F-GE180, is about 4 times higher than that of 11C-PBR28 [9]. We have argued ourselves for a more liberal use of clinically justified radiation, even in children [10], but delivering a higher radiation dose to obtain images of much lower quality in a potentially more radiosensitive population of abused children should not be condoned.
Finally, child abuse has important legal ramifications [11], and it is not difficult to imagine the human and financial cost of a misdiagnosis caused by unreliable images produced by a failed tracer.
Acknowledgments
This work was supported in part by the Intramural Research Program of the National Institute of Mental Health, National Institutes of Health (project number ZIAMH002852). The views expressed in this article do not necessarily represent the views of the National Institutes of Health, the Department of Health and Human Services, or the United States Government.
Footnotes
Declarations
Conflicts of interest None
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References
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