Frequent body CT scanning of young adults: indications, outcomes, and risk for radiation-induced cancer.

PURPOSE: The aims of this study were to define the magnitude of frequent body CT scanning of young adults and to determine associated patient diagnoses, examination indications, short-term outcomes, and estimated radiation-induced cancer risk.
METHODS: Patients aged 18 to 35 years who underwent chest or abdominopelvic CT between 2003 and 2007 at any of 3 hospitals were identified and categorized by total number of scans per body part as rarely (<5), intermediately (>5 and <15), or frequently (>15) scanned. Medical records of the frequently scanned were reviewed. Cumulative radiation exposure, calculated from typical effective doses, was used to estimate cancer risk. Cancer incidence and mortality were estimated using the Biological Effects of Ionizing Radiation method.
RESULTS: A total of 25,104 patients underwent 45,632 scans, of whom 23,851 (95%) and 70 (0.3%) were rarely and frequently scanned, respectively. Among frequently scanned patients, the most common diagnoses were cancer (19 of 36 [52.8%]) and cystic fibrosis with lung transplantation (11 of 36 [30.5%]) for chest CT and cancer (25 of 34 [73.5%]) for abdominopelvic CT. During the mean 5.4 years (range, 0.9-7.6 years) of follow-up, 46% of frequently scanned patients (32 of 70) died. Of the 47 cancers predicted in the entire cohort, 36 (77%) and 2 (3%) were expected in the rarely and frequently scanned.
CONCLUSIONS: The majority of CT-induced cancers are predicted to result from sporadic rather than frequent scanning. Frequent scanning confers a significant cancer risk but occurs in severely ill patients, a large proportion of who die before any radiation-induced cancer would be a factor in their health.