HOLLYWOOD, Fla. — Over time, radiation exposure, even at lower doses than recommended thresholds, has adverse consequences for physicians who perform interventional procedures.
According to a panel of speakers at the International Symposium on Endovascular Therapy, physicians who perform and assist in interventional procedures have higher rates of cancer, cataracts and brain tumors compared with the general population. In addition, those who perform and assist in endovascular procedures have elevated risk for musculoskeletal problems due to the physical demands of such procedures, and may have greater risk for accelerated vascular aging.
‘No safe dose’
Lindsay Machan, MD, associate professor in the department of radiology, associate member of the division of vascular surgery and associate member of the department of urologic sciences at the University of British Columbia, Vancouver, said during the session that “there is no safe dose of radiation. That is becoming abundantly clear.”
According to Machan, everyone “has very different levels of repair genes after they are hit by a photon, and there is no test as of yet to find these repair genes. So you really don’t know how susceptible you are. But the brain and the eyes are much more sensitive than were previously thought and, more disturbingly, the person whom you’ve relied on to tell you how much radiation is safe almost certainly doesn’t know this.”
Interventionalists are at risk as a result of cumulative radiation exposure over years or decades, and have performed more complex procedures over time, he said. Machan noted that most existing safety guidelines are based on acute exposure to large doses of radiation, so current guidance may not provide adequate protection.
He said one study of 223 people involved in interventional cardiology procedures and 222 controls “found a statistically significant difference in left and right carotid intima-media thickness” between those exposed to high doses of radiation and those not exposed, as well as differences in leukocyte telomere length, which is associated with early mortality. This suggests “evidence of accelerated vascular aging” as a result of radiation exposure, he said.
A possible mechanistic explanation for some of the findings is that excessive exposure to radiation appears to overcome the repair genes’ ability to function, Machan said.
Potential implications of this knowledge are increased regulation, new technologies being developed to combat the problems and interventional cardiology becoming a less desirable career choice “unless we really get on top of this,” Machan said.
In the meantime, interventional cardiologists should strictly adhere to all radiation safety practices, he said.
Chet R. Rees, MD, clinical professor of medicine at Baylor University Medical Center at Dallas, said physicians who perform interventional procedures are at increased risk of musculoskeletal problems because of the need to wear heavy aprons to protect against radiation exposure while spending time in awkward positions.
Compared with other medical professions, interventionalists are more likely to be treated for neck pain, back pain and herniated cervical disks, Rees said.
He cited data from a study showing that electrophysiologists who wear heavy aprons are at increased risk for spondylosis and cervical spondylosis, and the risk increases with age and number of years in practice. Those aged 50 years and older and those who have been performing such procedures for 20 years or more have a greater risk, he said.
According to results of a membership survey from the Society of Cardiovascular Angiography and Interventions, about half of interventional cardiologists reported musculoskeletal injuries, which was more likely with higher case load and age, he said.
An issue could be that “the forces on the spine can be much greater than the actual object that you are bearing the weight on, such as an apron,” he said. Repetitive lifting, which bears some resemblance to habitual heavy-apron wearing with regards to tension of the cervical spine and its attached muscles, is strongly associated with musculoskeletal injury, he noted. Effects of constant tension from the apron in the neck area could also be a factor.
Maintaining fitness, especially core fitness, and proper weight can help prevent these issues, Rees said. It can also help to follow proper ergonomics, such as keeping monitors in front and at eye level, twisting one’s whole body instead of just the neck, changing up which foot hits the pedal, avoiding being static for a prolonged time and wearing belted instead of unbelted aprons.
Wearing a lightweight apron is not a solution, because they don’t provide enough protection against the kind of radiation exposure in interventional procedures, Rees said.
“Attitudes are shifting, however,” he said. “People who talked about these things used to be considered crybabies, but this has caused people to propose treating this more like radiation safety, with a culture of education, prevention, infrastructure and more widespread knowledge.”
Machan said research from the past 20 years has determined that “there is absolutely no threshold for cataract development. In other words, the idea that you reach a threshold dose and then something bad happens unfortunately … is not true.” He noted that in one study up to 40% of physicians and staff involved in interventional procedures had cataracts, and other studies have found that radiation exposure is more strongly linked to cataract development than previously thought.
While most people who develop cataracts have anterior cataracts, interventionalists have a high rate of posterior cataracts — for which one of the only known causes is radiation exposure.
Traditionally, the threshold for protection from developing cataracts from radiation exposure was considered to be 150 mSv/year, but researchers studying people who helped clean up the Chernobyl nuclear disaster concluded that “if a threshold exists at all, it must be well below 100 mSv/year. The yearly allowable dose is probably zero but is certainly well below 100 mSv/year.”
Troublingly, cataract development often seems to occur “after relatively short times in practice,” he said.
All people in the cath lab should be wearing lead glasses, and the proper kinds vary by procedure and how close one is to an image intensifier, he said. Face shields, whether ceiling-suspended or worn around the head, should also be used, he said.
“The lens in everyone is more radiosensitive than anyone ever thought,” Machan concluded. “In addition, there is an unknown percentage of us that are genetically predisposed to be even more sensitive to radiation.”
While there are few hard data on brain tumors as a result of radiation exposure from the cath lab, the literature suggests that there may be a connection, William Gray, MD, system chief, division of cardiovascular disease, Main Line Health, and president, Lankenau Heart Institute, Wynnewood, Pennsylvania, said during the session.
“The probability of occurrence increases with the effective radiation dose, but the severity of the cancer it incites is independent of that dose,” he said.
While in the general population, brain tumors occur evenly on the left and right sides of the brain, studies of interventional cardiologists with brain tumors indicate that they overwhelmingly occur on the left side “which suggests that something unusual is going on in this community,” Gray said.
He added that although this pattern of distribution is disturbing, and the types of tumors seen are those typically associated with radiation, it is difficult to know with certainty if the incidence of brain tumors among interventionalists is in fact greater than in the general population.
What is needed is more education, proper shielding practices and adjustment to fluoroscopic technique, he said, citing as examples of the latter minimizing time and images, minimizing angulation and maximizing distance from the radiation source when possible. – by Erik Swain
Gray W, Machan L, Reed CR. Session I: Town Hall – Managing the Lifetime Risks of Being an Interventionalist. Presented at: International Symposium on Endovascular Therapy; Feb. 6-10, 2016; Hollywood, Fla.
Rees reports receiving royalty income from CFI Medical Solutions. Gray and Machan report financial ties with various medical device companies.