Acute Care Needs Outweigh CT-Related Cancer Risk

Larry Hand

February 05, 2013

Young adults who have had 1 or more computed tomography (CT) scans earlier in life are at significantly greater risk of dying from underlying medical conditions than from radiation-induced cancer, according to a study published online February 5 in Radiology. Therefore, models that assume perfect health in estimating radiation-induced cancer risk should be reassessed to address underlying patient conditions, the researchers write.

Robert L. Zondervan, BA, from the Department of Radiology at Massachusetts General Hospital, Boston, and colleagues analyzed the records of 21,945 patients aged 18 to 35 years who underwent 16,851 chest and 24,112 abdominopelvic CT exams between January 1, 2003, and December 31, 2007, at 3 Boston hospitals affiliated with Harvard Medical School.

During 5.5 years of follow-up, 575 (7.1%) of 8057 patients who received chest CT died and 546 (3.9%) of 13,888 patients who received abdominopelvic CT died. The researchers confirmed mortality status through social security records.

In contrast, the researchers estimated the percentage of cancer deaths that would be caused by the CT would be just 0.1% of each group (P < .01 compared with mortality resulting from the underlying medical issue). For the estimate, they used the Biologic Effects of Ionizing Radiation VII method, which accounts for age, sex, and magnitude of exposure and assumes no underlying comorbidities.

Cancer was the most common reason for chest CTs, at 31.6%, compared with trauma, at 14.8%. For abdominopelvic CTs, the most common reasons were abdominal pain (19.8%) and cancer (19.6%), followed by trauma (10.4%).

In a subgroup analysis, the researchers found that when patients with cancer were excluded, the mortality risk resulting from underlying medical conditions remained significantly higher than the risk resulting from CT-related cancer deaths. Specifically, the number of patients who received chest CT who died during follow-up totaled 300 (4.7%) of 6439 patients, and the number of patients who received abdominopelvic CT who died totalled 309 (2.5%) of 12,472 patients. Again, the predicted percentage of CT-related cancer deaths amounted to 0.1% (all P < .001).

Among patients who had only a single CT exam, 220 (3.6%) of 6106 patients who received chest CT died (compared with an estimated 2 CT-related cancer deaths in the group), and 223 (2.2%) of 9945 patients who received abdominopelvic CT died (estimated 4 CT-related cancer deaths).

"A Bit Surprising"

"It was a bit surprising to see how high the five-year mortality rate was in this group," Susanna I. Lee, MD, PhD, senior author and chief of women's imaging at Massachusetts General, said in a related news release. "To put it in context, the average young adult has only a 1 percent chance of dying in the next five years" compared with 7.1% for those who had received a chest CT and 3.9% of those who received an abdominopelvic CT.

The researchers point out that they did not measure benefits of imaging, which would require a controlled randomized trial, and designing such a trial "is methodologically challenging." In addition, the researchers note that their results, obtained from 3 university-affiliated hospitals, might not be generalizable to other geographic areas.

Much of an ongoing debate about potential risk for radiation-induced cancer "is hampered by lack of reliable data on how often and in which medical scenarios we are deriving the benefits," the researchers write.

"We're not saying be complacent about the radiation risk from CT," Dr. Lee said in the news release. "But these people being imaged might have been in a motor vehicle accident, or have a perforated appendix or life-threatening cancer, and we're trying to gain information from scans that can help them. That's the part that gets lost in the debate."

In conclusion, the researchers write, "When consulting on radiation concerns, the radiologist should counsel that the underlying medical morbidity, rather than CT-induced cancer, is the much greater driver of a potentially adverse patient outcome."

The authors have disclosed no relevant financial relationships.

Radiology. Published online February 5, 2013. Abstract