Internal Audit to Monitor the Injected Activity in PET/CT Using Control Charts

In an effort to limit the risks associated with medical radiation exposure, the last century witnessed the development of dose control mechanisms, recommended by the International Commission on Radiological Protection. This organization recommends the optimization of radiation protection to provide the highest level of safety that may reasonably be achievable. Adhering to the "as low as reasonably achievable" principle, the purpose of this study was to monitor the 18 F-FDG injected activity in PET and optimize the radiation protection through an internal audit process. This monitoring allows the identification of opportunities for improvement in patient care and safety, as well as to establish a periodic review of the medical unit reference levels.

The methodology is based on short run Quesenberry (Q) statistics and normalized nonconstant sample size (Z-chart) control charts. Anonymized data from 512 patients were selected from a set of 18 F-FDG PET/CT (Siemens, Biograph 6) examinations performed during 10 months. The analyzed variable was the ratio between the 18 F-FDG injected activity (MBq) and patient weight (kg).

Mean injected 18 F-FDG activity was 347.811 ± 64.967 MBq corresponding to a mean effective dose of 6.608 ± 1.234 mSv. The ratio between the 18 F-FDG injected activity and the body mass of patients was reduced from 5.243 ± 0.716 to 5.171 ± 0.672 MBq/kg during the statistical data analysis. The study demonstrates that control charts can be a useful tool to signal situations where patients receive an activity significantly different from the standard practice in a medical unit.

The use of joint control charts is a suitable tool for detecting nonoptimized radiopharmaceutical administration. This analysis provides opportunities to evaluate and improve the quality of practice in nuclear medicine. This methodology constitutes an internal audit that may help health care professionals to make appropriate decisions to ensure all patients receive the safest and most appropriate care.