Slim chance: Morbidity poses larger mortality risk than CT for young adults

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 - radiation dose, CT

The risk of death from underlying medical morbidity far outweighs the risk of death from radiation-induced cancer among young adults undergoing body CT imaging. The study was published February 5 in Radiology.

As concerns regarding the risk of radiation-induced cancer have emerged, the need to put the risks and benefits of CT exams in a clinically relevant context has manifested.

“The impetus for our study was the concern that the lay press often focuses on potential harm caused to patients by CT imaging,” Susanna Lee, MD, PhD, chief of women's imaging at Massachusetts General Hospital in Boston, said in a press release. “Lacking in this discussion is a sense of how sick these patients already are.”

Robert L. Zondervan, MS, from the department of radiology at Massachusetts General Hospital in Boston, along with Lee and colleagues sought to quantify patient outcome and predicted cancer risk from body CT in young adults. They also aimed to identify common indications for CT imaging.

The researchers designed a retrospective multicenter study and focused on the medical records of 16,804 patients ages 18 to 35 years old with a social security number who underwent a chest or abdominopelvic CT from January 1, 2003, to December 31, 2007. The patients underwent 16,851 chest CT exams and 24,112 abdominopelvic exams.

In the chest CT group, 7.1 percent of patients died during the 5.5-year follow-up. A total of 0.1 percent of these patients were predicted to die of radiation-induced cancer, according to the Biological Effects of Ionizing Radiation (BEIR) VII method.

In the abdominopelvic CT group, 3.9 percent of patients died during follow-up. Again, 0.1 percent of these patients were predicted to die of radiation-induced cancer, according to the BEIR VII method.

The risk of death remained substantial even for noncancer patients. “When we subtracted out cancer patients from the data set, the risk of death in the study group ranged from 2.5 to 5 percent—still well above the risk in the general population,” Lee said.

In young adults undergoing body CT, the estimated risk of death from radiation-induced cancer was “far outweighed” by the risk of intercurrent death presumably from underlying morbidities, according to Zondervan et al. A patient’s underlying medical morbidity, rather than CT-induced cancer, is the dominant factor driving a potentially adverse outcome, the researchers continued.

The researchers noted that most radiation-induced cancers are predicted in patients who are very rarely scanned, and most patients were very rarely scanned.

A total of 6,620 of the 8,057 chest CT patients underwent one to two scans. Meanwhile, 884, 505 and 48 chest CT patients underwent three to five scans, 6 to 15 scans and more than 15 scans, respectively.

Among the 13,888 abdominopelvic CT patients, 11,905 underwent one to two scans. A total of 1,334 underwent three to five scans, 606 underwent 6 to 15 scans, and 43 underwent more than 15 scans.

“These results emphasize that radiologists should also focus radiation reduction efforts on patients who are very rarely scanned, and not just on those who are more frequently scanned.”

The most common indications for chest CT, in order of frequency, were: cancer, trauma cardiac complaint and respiratory complaints. The most common indications for abdominopelvic CT, in order of frequency, were: abdominal pain, cancer, trauma, urinary tract disease, bowel-related complain and cardiopulmonary complaints.

Limitations of the study included the uncertain validity of the BEIR VII model, particularly at low levels, and the variability of patients’ actual radiation exposure.