A Two-Year Retrospective of a Quantitative SPECT Quality Control Program
Abstract
Purpose
Nuclear medicine is undergoing a paradigm shift to produce images in units of activity concentration, analogous to PET imaging. Quantitative SPECT imaging requires system calibrations. In 2024, we formally incorporated routine quantitative calibrations and verification measurements into our comprehensive SPECT quality assurance (QA) program. Here we present a retrospective evaluation of the quantitative Tc99m QA program for our eight Siemens Intevo Bold SPECT/CT systems.
Methods
Siemens xSPECT sensitivity calibrations for Tc99m imaging were performed quarterly using NIST-traceable, long-lived Co57 precision sources. Subsequent verification measurements were performed using our standard ACR Jaszczak phantom preparation and acquisition protocol. Phantom data are reconstructed both quantitatively, to evaluate calibration accuracy, and non-quantitatively, to maintain consistency with existing QA trend analyses. Reported sensitivity values were compared to expected nominal values provided by Siemens, and measured total phantom activities were compared to known input total activities.
Results
A two-year retrospective evaluation of quantitative performance across our fleet demonstrates robust and stable calibration using Siemens xSPECT sources. Across the eight systems, sensitivity calibrations performed with NIST-traceable Co57 sources remained consistent over time, with only three systems exhibiting sensitivity coefficient of variation (COV) greater than 1%, and a maximum observed COV of 2%. Although Siemens defines internal trigger limits for sensitivity calibration, our institution implemented a more restrictive +/- 5% acceptance criterion for calibration verification. This threshold was only exceeded 3 times, each on separate systems. In all cases, the issue was resolved through replacement of the calibration source. Across all systems, the average verification error for any individual system did not exceed 4% (minimum average deviation of 1.8% and maximum deviation of 3.8%).
Conclusion
Quantitative SPECT calibration and verification has been successfully integrated into our clinical QA program, supporting reliable longitudinal quantitative performance in a multi-system clinic. Longitudinal evaluation of our Lu177 QA program is underway.