Frequent CT scanning not linked to cancer development
MedWire News: Study findings suggest that the majority of computed tomography (CT)-induced cancers occur among rarely, rather than frequently, scanned patients.
"Frequent scanning confers a significant cancer risk but occurs in severely ill patients, a large proportion of whom die before any radiation-induced cancer would be a factor in their health," say Robert Zondervan (Massachusetts General Hospital, Boston, USA) and co-authors.
The researchers performed a retrospective study of 25,104 patients aged 18-35 years who underwent chest or abdominopelvic CT at three academic medical centers between 2003 and 2007. Patients were categorized by total number of scans per body part as rarely (<5 exams), moderately (>5 and <15 exams), or frequently (>15 exams).
Cumulative radiation exposure was used to estimate cancer risk, with effective dose estimates of 7 mSv and 10 mSv assigned to chest and abdominopelvic CT scans, respectively. Cancer incidence and mortality were calculated using the Biological Effects of Ionizing Radiation method.
In total, 18,592 chest and 27,040 abdominopelvic CT scans were performed, with 95.0% of patients rarely scanned and 0.3% frequently scanned.
The most common diagnoses among the 36 patients undergoing frequent chest CT scanning were cancer (52.8%) and cystic fibrosis with lung transplantation (30.5%), while cancer was most frequently diagnosed among the 34 patients receiving routine abdominopelvic CT (73.5%).
Sarcoma was the most common diagnosis in the cancer follow-up category, representing 19.0% of chest CT and 30.0% of abdominopelvic CT patients.
Among the 728 chest CT examinations, the most common indications included cancer follow-up (57.7%), signs of infection (17.0%), and lung transplant evaluation (16.7%). The most common indications for the 692 abdominopelvic CT examinations were cancer follow-up (54.9%), postoperative pain or fever (18.2%), and abdominal pain (8.8%).
After a mean 5.4-year follow-up period, 46% of frequently scanned patients died as a result of complications linked to pre-existing underlying disease.
The team estimated that the number of cancers attributable to CT scanning would be 36 (0.2%) in the 23,851 rarely scanned patients and two (2.2%) in the 70 frequently scanned patients.
Thus, of the 47 cancers associated with CT screening predicted for the whole population, 76% are linked to rarely scanned patients, the team writes.
"Reducing sporadic CT scanning in young patients will require changes in patient attitudes toward medical uncertainty. Ultimately, society as a whole must agree at what point the marginal long-term risks incurred for that certainty is too great," conclude the researchers in the Journal of American College of Radiology.
By Ingrid Grasmo