Diagnostic reference levels of CT radiation dose in whole-body PET/CT

The role of CT in PET/CT imaging includes acquisition techniques for diagnostic, anatomic localization, and attenuation correction purposes. Diagnostic reference levels of the volumetric CT dose index (CTDI_vol) are available for dedicated CT procedures on selected body regions, but similar reference levels for whole-body CT used in PET/CT examinations are limited. This work reports CTDI_vol values from sites that conduct whole-body oncologic PET/CT examinations and participated in the scanner validation program of the Society of Nuclear Medicine and Molecular Imaging Clinical Trials Network. Methods: From 2010 to 2014, a total of 154 sites submitted CT acquisition parameters used in their clinical ¹⁸F-FDG PET/CT oncology protocols. From these parameters, the CTDI_vol was estimated using the ImPACT CTDI dosimetry tables. Histograms of CTDI_vol values were created for each year, and descriptive statistics, incluDing mean, median, and 75th percentile, were reported. Repeated-measures ANOVA was performed to determine whether significant differences occurred between reporting years. Results: A wide range of technical parameters was reported, most notably in tube current. Between 2010 and 2014, the median CTDI_vol ranged from 4.9 to 6.2 mGy and the 75th percentile from 9.7 to 10.2 mGy. There was no significant change in CTDI_vol between reporting years (repeated-measures ANOVA, P 5 0.985). Conclusion: The 75th percentile CTDI_vol reported in this work was 9.8 mGy averaged over all reporting years. These data provide a resource for establishing CTDI_vol reference values specific to performing CT in PET/CT whole-body examinations. The wide ranges of CT acquisition parameters reported by sites suggest that CTDI_vol reference levels may be beneficial for optimization of CT protocols.