Diagnostic Reference Levels in nuclear medicine for Positron Emission Tomography examinations: First Italian multicenter data collection

Introduction: Diagnostic Reference Levels (DRLs) are essential for optimizing patient protection in radiological imaging. PET/CT acquisitions are fundamental in modern nuclear medicine for diagnosis, staging and tumor response evaluation. The hybrid nature of PET/CT results in a total dose to the patient from both modalities. Therefore, it is appropriate to set and evaluate DRLs independently for each modality. While DRLs for some PET tracers are extensively described by various national and international guidelines, similarly established guidelines for the low-dose CT component are lacking. Methods: In 2022, a multicenter collaboration was established among three Italian Hospitals to evaluate dosimetric indices for almost 13,000 PET/CT scans using various scanner technologies and tracers. The dosimetric data were classified based on the radiopharmaceuticals injected and further stratified according to scan length: Whole Body (WB), head vertex-to-feet and brain. Results: The results for all tracers and imaging procedures evaluated are compliant with or lower than available DRLs. For some exam types, national DRLs are not currently defined and so typical values, calculated as the median of the data distribution in this study, are proposed. For the PET the typical values are proposed in terms of total and per kilogram administered activity, while for the CT they are proposed in terms of CTDIvol and DLP. Conclusion: In line with Directive 2013/29/Euratom, these collected data could be valuable for a future review of DRLs for both PET tracers and low-dose CT component in WB studies, and for defining new DRLs for low-dose CT component in vertex-to-feet and brain studies.