As medical uses increase, so does vigilance on exposure hazards.
Far from the days when patients had to undergo exploratory surgery to diagnose disease or have invasive procedures to treat illness, today's advanced radiology technologies can capture images inside the body in less than one heartbeat.
Radiation technology yields huge amounts of vital diagnostic information in a short period of time and can mean much more targeted, effective therapies for cancer, heart disease and other illnesses.
But does it come with a price? Although data are scarce and inconclusive regarding the link between medical radiation exposure and subsequent illness, physicians say the current thinking is to err on the side of caution.
“As a custodian of radiation, I want to be very judicious in how I use it,” says Thomas Buse, MD, medical director of radiology at OhioHealth Riverside Methodist Hospital. “In my mind, the medical community is very aware of radiation. Our awareness of potential risks, and the fact that we don't know all the details of a cause-effect relationship between radiation and illness, means we're very judicious.
“Every one of our protocols is designed with radiation dose at the forefront of our thinking,” Buse adds.
In the last few decades, the number of CT scans done annually in the United States has soared, from about 3 million in 1980 to more than 80 million in 2015.
There's a reason for that, says David Hintenlang, professor and chief of medical physics in the Department of Radiology at Ohio State University Wexner Medical Center. The tests are vital to making informed decisions in patient care. “We reap a lot of benefits. With the breakthroughs we've seen in technology, you can get a huge amount of information very quickly.”
More recently, the medical community is paying closer attention to whether radiation might be overused in some cases.
Risks from radiation come primarily in two forms: deterministic and stochastic. Deterministic effects are directly related to exposure and occur when a dose threshold has been exceeded. Examples include cataracts and skin irritation or burns, Hintenlang says. Stochastic effects, which pertain to cancer, occur by chance, and while there is no dose threshold, the risk increases linearly as the dose increases.
Cancers can have a 10- to 20-year latent period, which makes it challenging to establish a cause-effect relationship, he adds.
With children in particular, that long latency period is cause for extra care, says Rajesh Krishnamurthy, MD, chief of the Department of Radiology at Nationwide Children's Hospital. Also, because children are growing rapidly, their cells are dividing rapidly, making them more susceptible to the effects of ionizing radiation, he says.
Historically, medical and scientific communities haven't been able to easily track radiation doses given to patients. The tool most widely used in establishing a link between radiation and cancer has been to extrapolate data from the World War II nuclear bombing of Hiroshima and Nagasaki.
Hintenlang says the National Cancer Institute has embarked on an initiative to look at CT doses retrospectively, but it the meantime, “It's very challenging to capture that data.”
One thing that is known, Buse says, is that the more frequently a patient receives radiation, the greater the risk. “The body has the potential to heal itself,” he says, “so having five scans in 10 days is very different than having five scans in 10 years.”
Certain conditions such as kidney stones, Crohn's disease, cardiovascular disease and cancer tend to require more frequent monitoring, Buse says. “If you're having multiple scans a year, it might be time to talk to your doctor and ask some questions.”
Other techniques, such as ultrasound and magnetic resonance imaging, do not use ionizing radiation and can be used instead in some cases, but it's not always an equal trade-off. MRIs are costly, while ultrasounds can be more difficult to interpret.
However, Krishnamurthy says, “If I can get the same benefit with another modality, should I use it? Absolutely.”
In both the diagnostic and therapeutic arenas, technologies such as filters, grids and shutter anatomy can lessen exposure, as can a technique known as “last image hold,” in which technicians turn off radiation during a procedure to adjust for patient movement or other factors. This prevents the exam from having to be repeated from the beginning, Hintenlang explains.
Clinicians can adjust the thickness of the “slices” obtained during CT, and sophisticated hardware can capture high-quality images in a short amount of time, lessening exposure and the need for repeat tests.
In radiation therapy, in which high doses are delivered to kill cancer cells, efforts focus on making the dose conform as closely as possible to the actual tumor volume, sparing nearby tissue. Medical physicists and dosimetrists are part of a team that can more precisely pinpoint where the dose should be aimed for maximum effect and minimum exposure, Hintenlang says.
In addition to criteria established by the American College of Radiology and other specialty groups, individual healthcare systems may develop their own protocols to safeguard against unnecessary radiation. For example, Hintenlang says, “A request for an unusually high dose sends an alert to our physics group that, ‘You might want to look at this.'”
Buse says OhioHealth employs a similar system of checks and balances. “When you input the patient's height, weight and other factors, our protocols will recognize if it will exceed the threshhold we have set and send a radiation dose alert by email. It's a moment for the technologist to pause and say, is this our only option, or can we alter the thickness of the CT slice, or can we scan just the pelvis instead of the entire abdomen?”
Radiology experts say part of their job is to educate colleagues on the appropriate use of CT scans and other imaging modalities.
“We think it's critical to provide physicians in the community with clinical decision support tools,” Krishnamurthy says.
Hintenlang says, ultimately, the decision comes down to patient need.
In most cases, Buse says, “The risk of not doing the test, in terms of missing a diagnosis or inadequately treating a patient, is far more significant. I'd much rather do the test.”
Krishnamurthy agrees. “Often, we have to step back and ask why are we doing this test? In the majority of cases, it's because we need to diagnose something in a timely fashion, or to see whether a patient is responding to treatment. Those steps can be lifesaving.”
Laurie Loscocco is a freelance writer.