While more research is needed, the available data suggest the benefits of surveillance far outweigh the risks.
Regular surveillance of unruptured intracranial aneurysms using computed tomography angiography (CTA) is associated with an excess cancer risk due to radiation exposure that is so small as to be far eclipsed by the risk of aneurysm rupture, according to a modeling analysis published online December 7, 2018, ahead of print in Stroke.
The study authors, led by Ajay Malhotra, MD (Yale School of Medicine, New Haven, CT), point out that unruptured intracranial aneurysms are being identified more often because of increased use of less-invasive imaging techniques with higher resolution. At the same time, the natural history of these aneurysms remains uncertain.
Current American Heart Association/American Stroke Association guidelines recommend follow-up involving magnetic resonance angiography (MRA) or computed tomography angiography (CTA) done “at regular intervals for patients managed without either surgical or endovascular intervention,” they point out. “However, the interval and duration of recommended follow-up are uncertain.”
Cumulative exposure to radiation is one concern surrounding repeated use of CTA for surveillance. Malhotra and colleagues say a reasonable surveillance protocol should not expose patients to an increased risk of cancer that outweighs the risk of aneurysm rupture.
For the study, they used a simulation-modeling approach to estimate the degree of increased cancer risk associated with radiation exposure from CTA surveillance for unruptured aneurysms. Each CTA performed as part of routine surveillance was assigned as a separate radiation exposure event. Malhotra et al used the Radiation Risk Assessment Tool, which is based on data from , to estimate the degree of increase cancer risk associated with each event.
Men and women starting surveillance imaging at 30, 40, and 50 years of age and receiving annual CTAs were considered as separate subgroups. As a comparison, the investigators also calculated the radiation-induced cancer risk in the same groups of patients, if they received CTAs every 2 and 5 years.
Based on their calculations, each CTA performed conveys an approximately 0.0026% excess lifetime cancer risk. CTA-associated excess cancer risk per exposure increased relatively more rapidly with the first 10 exposures and plateaued after the 44th exposure.
Cancer Risk Low Even in Highest-Risk Group
The major factors contributing to an elevated excess lifetime cancer risk were receiving CTA follow-up at a younger age, having more frequent CTA follow-up, having a longer CTA surveillance period, and being male.
The highest-risk group consisted of male patients receiving annual CTA follow-ups from age 30. In this group, the excess lifetime cancer risk was calculated to be 0.115% by age 81.
“Radiation-induced brain cancer incidence associated with [unruptured intracranial aneurysm] surveillance strategies is markedly low relative to the risk for aneurysmal rupture,” conclude the authors. They call for additional studies to further evaluate cost-effectiveness and utility of routine CTA surveillance.
Commenting on the study for Neurovascular Exchange, Joseph J. Gemmete, MD (University of Michigan, Ann Arbor), expressed surprise that the cancer risk was as low as the authors found it to be. On the other hand, he pointed out, those working in angiography suites have become increasingly aware of the risks associated with radiation exposure and are doing everything in their power to minimize it. This practice change, combined with newer machines that also minimize radiation exposure, are making imaging procedures far safer than they were in the past, he added.
Gemmete himself typically follows aneurysm patients using MRI and told NVX he has no plans to change that practice. He pointed out, however, that some patients, such as those with cardiac pacemakers, cannot undergo MRI. For such patients, CTA appears to be a safe option. “You don’t have to worry about [the increased risk of cancer],” he noted. “It’s real, but it’s so small that the benefits far outweigh the risks.”
Malhotra A, Wu X, Chugh A, et al. Stroke. 2018;Epub ahead of print.
Malhotra and Gemmete report no relevant conflicts of interest.