Patients undergoing multiple 18F-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 18F-FDGPET/CT examinations in a year. METHODS In a retrospective study performed at a tertiary care hospital, patients who underwent ≥2 18F-FDGPET/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 18F-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 18F-FDG PET/CT examinations any patient underwent in a single year was seven. 20.9% patients had ≥2 18F-FDG PET/CT exams in any single year. Thirty nine percent patients in the cohort were below 60 years age. The median dose for 18F-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 25th percentile, 50th percentile and 75th percentile as well as the mean to be over 100 mSv, with the 25th percentile being 109 mSv. The dominant primary malignancies contributing to serial 18F-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 18F-FDG PET/CT exams with one out of every 8 patients receiving cumulative dose ≥100 mSv and that includes patients with long life expectancy. ADVANCES IN KNOWLEDGE The study found that 1 of 5 patients had ≥2 18F-FDG PET/CT exams in a calendar year, 1 of 4 patients in two years and 1 of 8 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.