Patients undergoing multiple 18 F-FDG PET/CT exams: Assessment of frequency, dose and disease classification.

Objective: To analyse the frequency, demographics, primary disease and cumulative effective dose of patients undergoing two or more ¹⁸ F-FDG PET/CT examinations in a year.
Methods: In a retrospective study performed at a tertiary-care hospital, patients who underwent ≥2 ¹⁸ F-FDG PET/CT scans in a calendar year were identified for two consecutive years. The CT radiation dose was calculated using dose-length-product and sex-specific conversion factors. The primary malignancy of patients was retrieved from electronic medical records.
Results: 10,714 ¹⁸ F-FDG PET/CT exams were performed for 6,831 unique patients in 2 years, yielding an average of 1.6 exams per patient. The maximum number of ¹⁸ F-FDG PET/CT examinations any patient underwent in a single year was seven. 20.9% patients had ≥2 ¹⁸ F-FDG PET/CT exams in any single year. Thirty nine percent patients in the cohort were below 60 years age. The median dose for ¹⁸ F-FDG PET/CT examination was 25.1 mSv and maximum value reaching 1.7 to 2.9 times the median value. Cumulative effective dose (CED) was≥100 mSv in 12-13% of the patients. The cumulative dose for both years combined demonstrated the 25 ^th percentile, 50 ^th percentile and 75 ^th percentile as well as the mean to be over 100 mSv, with the 25 ^th percentile being 109 mSv. The dominant primary malignancies contributing to serial ¹⁸ F-FDG PET/CTs in decreasing frequency were melanoma, non-Hodgkin's lymphoma (NHL), gastrointestinal cancer, breast cancer and Hodgkin's lymphoma.
Conclusions: A sizeable number of patients undergo≥2 ¹⁸ F-FDG PET/CT exams with one out of every eight patients receiving cumulative dose≥100 mSv and that includes patients with long-life expectancy.
Advances in Knowledge: The study found that one of five patients had≥2 ¹⁸ F-FDG PET/CT exams in a calendar year, one of four patients in two years and one of eight patients received cumulative dose≥100 mSv. Top malignancies associated with serial imaging in decreasing order of frequency included melanoma, non-Hodgkin's lymphoma (NHL), gastrointestinal cancer, breast cancer and Hodgkin's lymphoma.