By Debra L. Beck

If variety is the spice of life, then life in interventional cardiology is rarely boring. However, the variations in how those working in the cath lab look at radiation safety cover the spectrum, from individuals who are very concerned to those exuding more of a don't-worry-be-happy vibe.

Sure, everyone is expected to follow the rules and regulations to limit exposure, but for some doctors the long-term effects of occupational radiation exposure are no big deal. One interventionalist (who will remain unidentified to protect the guilty) told us: "Every job has its risks and, anyway, my badge consistently indicates very minimal exposure at the end of the month." He did admit that he sometimes doesn't bother wearing his badge in the cath laboratory.

And those who worry? They feel passionately that radiation safety needs greater attention and study. The point of view expressed by Roxana Mehran, MD, would suggest there is no civil defense for the cavalier attitude expressed above. The professor of medicine and director of interventional cardiovascular research and clinical trials at Mount Sinai School of Medicine, New York City, told us: "It's a huge issue. As a female interventional cardiologist, it's central to what we think about, especially as we're all training during our child-bearing ages." But, she added, "It's not just about radiation, per se, it's also about protection against radiation, which then creates all these cath lab–related occupational hazards: back pains, varicose veins, and all kinds of things."

The reality: Cath lab personnel are chronically exposed to ionizing radiation and these exposures are steadily increasing, as is the evidence of harm.

Interventional cardiology and electrophysiology (EP) are booming, thanks to more diagnostic and interventional options (many of which will avoid surgical intervention and shorten hospital stays); longer, more complex procedures requiring greater radiation use; and a wider range of patients with indications for radiation-utilizing interventions. These advances combine to make occupational radiation exposure a very real issue for cath lab professionals, and one that is getting increased attention from individual groups and national societies. (From the 72 million CT scans performed in the United States during 2007, one study estimated 29,000 future cancers and 14,500 future deaths could develop due to radiation. Read our Featured Interview with the Mayo Clinic's Joerg Herrmann, MD, for a look at patient risk.)

Some recently published papers add to our knowledge on this topic. In the March issue of EP Europace, Professor Hein Heidbuchel of the University Hospital Gasthuisberg, University of Leuven, Belgium, and colleagues offer a European Heart Rhythm Association (EHRA) position paper on practical ways to reduce radiation doses for patients and staff during EP procedures, including device implantations.¹

A second paper, in the March 2014 issue of JACC Cardiovascular Interventions from a group led by Eberhard Kuon, MD, explores the impact of a mini-course on radiation safety offered to practicing interventional cardiologists at 32 cardiac centers in Germany.²

Beyond Fluoroscopy Time

Radiation in the cath lab is generated by using either fluoroscopy or cine angiography. While used far more often to guide catheter placement, fluoroscopy is responsible for only about 40% of total radiation exposure to staff and patients, according to the paper by Heidbuchel et al. Cine, on the other hand, which is generally reserved to capture the high-quality images used to generate a permanent record of the procedure, uses about 10 times the radiation as fluoroscopy.

Fluoroscopy time alone is insufficient for determining actual patient exposure, since it does not include cine imaging or take into account a number of other parameters. Since 2006, all interventional X-ray systems sold in the United States are required to measure and display actual patient dose burden, rather than just fluoroscopy time.

"The trouble with fluoroscopy time is that angulation will change the dose received by the patient, as will the frame rate," Charles E. Chambers, MD, director of the Cardiac Catheterization Laboratory at Penn State Hershey Heart and Vascular Institute and the president-elect of SCAI (2013–2014), told CSWN: Interventions. "So, if all you look at is fluoroscopy time—when your foot is on the pedal—you won't have a good sense of actual exposure. If you're going to do high-end interventional procedures—valves, total occlusions, complex interventions—wouldn't you want something that measures the actual dose rather than just fluoroscopy time?" he added.

Most modern X-ray systems can produce more complete patient dose reports that include relevant dose values, such as radiographic parameters and geometry factors, including angulations of the C-arm. This added information permits the retrospective calculation of the peak skin dose, if needed, and structured dose reports that will alert staff of a possible need for follow-up.

It Equals How Many Chest X-Rays?

Loads of ink have been devoted to the risk of radiation exposure to patients—from unnecessary testing, but also from increased use of imaging and intervention—but less has been said about the concurrent increased risk to the professionals who treat those patients. Yet, as Dr. Chambers pointed out in a 2011 editorial, physicians and cath lab staff are potentially exposed to lower single but higher cumulative radiations doses than patients undergoing complex procedures.³

The use of radiation in medical imaging and procedures has increased 6-fold in the last 20 years. According to the Prof. Heidbuchel's group, the typical annual exposure for an interventional cardiologist or a cardiac electrophysiologist is in the range of 5 mSv. That's equivalent to about 250 posteroanterior (PA) chest X-rays every year. For comparison, an "effective dose" equals 1 mSv and that's equivalent to 50 chest X-rays. The average dose received by Chernobyl evacuees was 30 mSv.

According to Patricia Best, MD, an interventional cardiologist at the Mayo Clinic, Rochester, Minnesota, the physician interventionalists consistently exhibit higher cumulative dosimeter readings than other personnel in the room, even though they likely spend fewer hours per week there. "We're closest to the patient," she told CSWN: Interventions.

Of note, the term "effective dose," or ED, was introduced to estimate radiological risk to workers, although it is also widely used to estimate risk for patients. Radiation exposure is often communicated to patients in terms of multiples of the dose from a chest X-ray, rather than by stating the risk of extra cancers. The "effective dose" for patients is considered very inaccurate, as is the estimation of increased cancer risk for an individual patient, noted Heidbuchel et al.

Protect to Serve
The evidence for occupational harm is compelling.

"Aging interventional cardiologists illustrate the consequences of both prolonged radiation exposure and radiation protective attire with cataracts, premature cancer risks, and spinal injury, pain, surgery," wrote Dr. Chambers in an editorial that accompanied the paper by Dr. Kuon and colleagues.⁴

Dr. Chambers concluded: "Without question, radiation safety is an important issue for patients, staff, and physician safety, but at what priority level does it reside for the busy interventionalist?" While we widely accept that interventionalists are at increased risk of posterior subcapsular lens opacities, for most, this risk is not a major cause of panic as cataracts are not life-threatening and can be countered with relatively simple, low-risk treatment. The push for lead glasses, which swelled about 20 years ago but dissipated, is growing again, Dr. Chambers noted. "Now they're pushing it again."

More concerning is recent research revealing a possible excess of brain tumors among cath lab physicians, with a hint of causality: In 2013, Ariel Roguin, MD, PhD, and colleagues reported on 31 cases of documented brain and neck tumors occurring in 31 physicians—23 interventional cardiologists, two electrophysiologists, and six interventional radiologists.⁵ A mean of 54.7 years old, all had worked many years in the cath lab, with a latency period before diagnosis of 12 to 32 years (mean = 23.5 years). Only one patient in the series was a woman.

The tumors included 17 cases (55%) of glioblastoma multiforme, two astrocytomas (7%), and five meningiomas (16%)—all malignancies known to be associated with radiation exposure. The most striking finding, according to the researchers, was that in the 26 cases where data were available regarding the side of the brain involved, the malignancy was left-sided in 85% of cases.

"Given that the brain is relatively unprotected and the left side of the head is known to be more exposed to radiation than the right, these findings of disproportionate reports of left-sided tumors suggest the possibility of a causal relation to occupational radiation exposure," they concluded.

"I'm not saying in any way that our profession is associated with an increased risk of cancer," Dr. Roguin told CSWN: Interventions. "It would be very difficult to prove causality because the numbers are so small; it could be just a matter of chance. All brain tumors have an equal chance of being left- or right-sided, and in this small series of patients there is left-side dominance that is not explained by anything other than radiation."

(Past) Time for a Registry

Although compelling, the data reported by Dr. Roguin and colleagues remain anecdotal and subject to the limitations inherent in interpreting observations from a "cluster" of cases without knowing the true numerator (all neck and brain cancers in interventionalists) and denominator (all interventional physicians).

Albeit only hypothesis-generating, the data highlight the lack of an ongoing registry to collect information on cancer cases in interventionalists, one that would include important elements such as confounding factors, radiation exposure levels, and smoking status.

"Thinking of the thousands of physician-years in the cath lab, wouldn't it have been nice to have started a database to measure this a long time ago?" said Dr. Chambers. "Do the physicians who do caths have a higher risk than those who do echo? We don't know these answers and it's a shame we haven't had that database in place." He added that SCAI is considering just such a registry.

Dr. Roguin stresses the importance of a determined focus on radiation safety. "When I've given talks about [the neck and brain malignancy data] at meetings, the reaction is generally a big 'wow,'" he said. "But, unfortunately, when you go to the big interventional meetings, maybe one session in 100 is on radiation protection."

He also noted that there are no sessions on how to stand correctly in the cath lab so as to avoid the orthopedic problems related to wearing the heavy lead protection. "Maybe it's just something that everyone is supposed to already know, but these are important issues."

Simple Adjustments, Striking Results

Many factors affect dose exposure in the cath lab. Prof. Heidbuchel's group focused mostly on EP procedures, but noted that radiation levels in the EP room are grossly comparable to those seen in the cath lab during PCI.

Operator-dependent factors that have been linked to reduced exposure include:

• Advanced training using a simulator
• Written reports post-procedure that include exposure amounts, and are provided to the patient and placed in the patient's file
• Cine substitution by stored fluoroscopy
• Optimized collimation
• RAO projection versus AP or LAO projections
• Pulsed fluoroscopy with a lower frame rate (≤6 fps vs. ≥12.5 fps)
• Avoiding pelvic radiation, particularly to young female patients

For many applications, fluoroscopic images suffice and render high-quality cine unnecessary. "This includes, for instance, angiography of the heart chambers or the pulmonary veins," said Heidbuchel et al. When cine is needed, its acquisition should be kept as short as possible, with a reduced frame rate and optimal collimation. Just a reduction of frame rate, from 25 fps, which is the nominal setting on many systems, to 3 fps, sufficient for most EP procedures, can reduce radiation dose by up to a factor of 8.

"The Photons Didn't Have a Chance!"

Of course, most dosing information produced during an intervention refers only to the patient, not the physician and ancillary staff, "because personal dosimeters don't give you instantaneous results," noted Dr. Chambers. "But all of these safety measures are for physician safety too."

One of the most important patient-dependent factors modulating doses in the cath lab is body habitus, with scattered radiation from the patient providing the main source of exposure for the operatorand other personnel in the room.

Using data from the University Medical Center Utrecht, the Netherland, Prof. Heidbuchel and colleagues showed that the difference in the radiation dose used in patients who underwent pulmonary antrum isolation with sequential radiofrequency applications varied approximately 6-fold between patients with a body mass index of 20 and 40.

"The same factor also applies for the level of scattered radiation in the cath lab," said Dr. Heidbuchel. "Therefore, the patient's constitution has a major influence on the dose rate for all persons in the room, and reducing the patient exposure will directly translate into reduced exposure of the cath lab personnel."

"What people don't realize is that, let's say with an obese patient, the quality of the image is going to suffer," Dr. Chambers said. "I tell people, ‘The photons didn't have a chance.' You can't get all the angulations, and may have more difficulty using some of the shielding... it all goes into the risk-benefit equation."

Shielding Above All

Just like with Captain America, the first line of defense against radiation exposure remains proper shielding.

"Current shielding protects you from about 90% of the dose, but some doctors don't wear all their leads or aren't careful enough with dosimeters," said Dr. Chambers. And some leave it to chance. For example, he pointed out, if a clinician opts to wear leads that don't offer full back protection, turning his or her back to the table when someone is fluouro-ing may expose him or her to a blast of ionizing radiation.

"If the lead doesn't fit properly, it won't protect completely," added Dr. Best. "It has to fit snuggly around the arms."

Prof. Heidbuchel's group shows the huge benefit gained from greater care towards shielding. Using a Rando® Phantom during a device implantation simulation, they found that a custom 0.5 mm lead screen, made of 50 x 50 cm2 apron material and hung on a custom Plexiglas arm support designed to shield the upper part of the patient's arm, as well as the left side of the patient from the operator, can reduce operator exposure 22–94% depending on the projection angle and measurement location.

The balance between imaging needs and radiation exposure is constant, and equipment manufacturers are primarily concerned with image quality, with their systems tuned accordingly, Heidbuchel et al. said. However, the simple measures they discuss have the potential to reduce the effective patient dose and scatter radiation toward personnel by "a staggering 95% or more!"

Pregnant Pause in the Cath Lab

Only 5.9% of board-certified interventional cardiologists in the United States are women. This number is increasing, Dr. Best noted. While women currently account for 49% of all medical school students, only 18% of cardiology fellows and only 8.7% of interventional cardiology fellows are women.

"Certainly exposure to radiation is a concern we see with our trainees and younger women who are thinking about having a family," said Dr. Best. "These women are concerned about radiation exposure during pregnancy, and rightfully so."

In 2011, Dr. Best led a group of researchers from the Women in Innovations (WIN) Group that published a SCAI Consensus Document on occupational radiation exposure to the pregnant cardiologist and technical personnel in the cath lab.⁶ After assessing the available research, albeit limited, they concluded that "current data do not suggest a significant increased risk to the fetus of pregnant women in the cardiac catheterization laboratory and thus do not justify precluding pregnant physicians from performing procedures in the cardiac catheterization laboratory."

Dr. Best feels the risk appears to be small. "You have to piece together the evidence from the little data that are out there on radiation exposure in other situations and the risk of malformations and malignancies, but when you look at the actual data, the risk is quite low if you're properly shielding and properly monitoring your radiation," she said.

"That said, I also think women have the right to choose if they want to personally pull themselves out of an area of radiation exposure during that time period."

One thing Dr. Best and her colleagues found surprising when preparing their SCAI paper is that in several US and European institutions maintain policies prohibiting women from declaring pregnancy and working in the cath lab.

She noted that such restriction is actually illegal in the United States, as it contravenes the Pregnancy Discrimination Act passed in 1978, which is an amendment to the sex discrimination section of the Civil Rights Act of 1964. "I think what it mostly does is discourages women from saying they're pregnant, and then they don't get proper monitoring and take proper precautions!"

When she herself was pregnant the first time, Dr. Best opted to continue working in the cath lab but wore double leads for the first trimester and a second dosimetry badge under her lead for the duration. During her second pregnancy she felt less nervous and opted to only wear one set of lead shielding.

"The badge always read ‘non-detectable,' again with careful and proper shielding," she said. "If the exposure is so small that it can't be detected on our badges, it's likely to be small enough to not make an impact."

Radiation Consciousness in the Cath Lab

The cath lab needs clear and effective physician leadership, stressed Dr. Chambers, and job one for the interventional cardiologist. "The interventional cardiologist has so many things to be concerned about, but at the end of the day, their job is to control what happens in the cath lab.

"They have to manage radiation the same way they manage contrast, the same way they manage stents. They have to manage the entire procedure, and radiation dose is part of that procedure."

Radiation dosing management should begin with pre-case discussion: knowing who the patient is, what they need, what's the plan, the importance of the consent form, he added. "Don't wait until you're part-way through the procedure or at the end of the procedure to realize you've given too much."

During the case, dosing should be managed in real-time, with safeguards in place to limit too much exposure. "When you hit a certain threshold of dose, the staff should let you know!" he said. In some situations, dose limits are included in practice protocols.

According to Dr. Best, Minnesota has very clear-cut limits, which, if exceeded, will trigger a requirement to report the case to the state. "I think these rules are very good at keeping numbers low—not that we will never exceed them—but it keeps you engaged," she said. "If you're not monitoring it, it won't change." It's also standard practice at her institution to put the radiation dose in every cardiac cath report.

References

1. Heidbuchel H, Verhamme P, Alings M, et al. EP Europace. 2013;15(5):65-51.
2. Kuon E, Weitmann K, Hoffmann WW, et al. JACC Cardiovasc Interv. 2014 March 13. [Epub ahead of print]
3. Chambers CE. JACC Cardiovasc Interv. 2011;4(3):344-6.
4. Chambers CE. JACC Cardiovasc Interv. 2014 March 13. [Epub ahead of print]
5. Roguin A, Goldstein J, Bar O, Goldstein JA. Am J Cardiol. 2013;111:1368-72.
6. Best PJ, Skelding KA, Mehran R, et al. Catheter Cardiovasc Interv. 2011;77:232-41.