BRAIN Study Confirms Higher Radiation Dose to Cardiologists’ Left Side

Radiation exposure to the cranium is higher on the left than on the right side for cardiologists doing invasive procedures, though this difference can be attenuated by wearing a nonlead-based cap in the cath lab, according to a study published in the August 17, 2015, issue of JACC: Cardiovascular Interventions.

For the BRAIN (Brain Radiation Exposure and Attenuation During Invasive Cardiology Procedures) study, Ehtisham Mahmud, MD, of the University of California, San Diego (La Jolla, CA), and colleagues assessed 7 cardiology fellows and 4 attending physicians (mean age 38.4 years; all men) at their institution as they performed diagnostic and interventional cardiovascular procedures (mean 66.2 cases per operator; mean fluoroscopy time 14.9 minutes).

Each participant wore a lightweight XPF attenuating cap (BLOXR; Salt Lake City, UT) containing barium sulfate and bismuth oxide. All caps were fitted with 6 dosimeters to measure radiation exposure on the outside and inside of the cap.

A Little More on the Left

Total exposure on the outside of the cap was numerically higher on the left than center location (106.1 vs 83.1 mrad; P = .075), but exposure in both areas was higher than on the right side (50.2 mrad; P < .001 for both). Total exposure inside the cap was similar for all 3 locations—ranging from 41.8 to 42.3 mrad—and was only slightly higher than that measured by the ambient controls (38.3 mrad; P = .046).

After accounting for the ambient radiation, outside left exposure was 16 times higher than exposure on inside left and 4.7 times higher than that on the outside right (P < .001 for both). Exposure on the outside center was 11 times higher than on the inside center of the cap (P < .001), but no difference was seen between outside and inside doses on the right side.

Among a variety of factors—including patient weight, patient BMI, operator height, operator weight, percentage of radial cases, fluoroscopy time, and dose area product—only operator training level (fellow in training or attending cardiologist) predicted the extent of radiation exposure on the outside left and center locations.

Attending cardiologists—who tend to stand in the secondary position farther from the radiation source—received more outside left and center radiation than did fellows, who usually stand in the primary position (P = .002 and P = .01, respectively). “Despite the decreased exposure to the second operator as explained by the inverse square law, the optimal use of shielding in favor of the primary operator may overcome the protection offered by the increased distance,” Dr. Mahmud and colleagues suggest.

The Cap is Only the Beginning

In a telephone interview with TCTMD, Dr. Mahmud said the value of the study is “not as much about the cap as the concept.” Regardless of what protection operators may or may not use, “the most important message of this paper is that the left side of the brain gets tremendously greater exposure to radiation,” he said.

“We're not doing a whole lot to protect ourselves… whether it’s in the primary or secondary position,” Dr. Mahmud continued. “One option is this cap, but the reality is we need to do a lot more to further understand and design equipment… or to look at alternative ways to do the procedure.”

Stephen Balter, PhD, of Columbia University Medical Center (New York, NY), told TCTMD in a telephone interview that the overall exposure reported outside the cap in the study is “reasonable” and well within the regulatory guidelines of 15,000 total mrad per year.

That said, using the cap “certainly doesn’t hurt,” he commented, and the fact that it can be used multiple times makes it less expensive than other options.

It is well known that radiation exposure is greater on the left than right side of cath lab operators, Dr. Balter explained. “It’s just how they stand and how they look at the monitors.” But “tracking people and understanding what’s happening is very relevant,” he said, adding that more specific results should come in time with theoretical modeling studies.

There will never be enough epidemiological research to show whether the XPF cap and other protections are increasing safety, Dr. Balter said. “There is a theoretical gain based on the radiobiology of models,” he added. “But it’s a small gain based on these numbers.”

All About Education

Dr. Mahmud said his team is planning another study, known as BRAIN 2, to further examine the phenomenon of how operator position affects radiation exposure. “The primary position is actually often better protected than the secondary position, where you’re a little bit further away but you might get more exposure to scatter,” he explained. “This is probably the first time this has ever been measured and ascertained.”

The second study will assess the validity of the difference between positions, Dr. Mahmud said. “We’re actually going to measure in a very systematic manner the radiation exposure for operators in the primary and secondary positions and behind and in front of shields.” BRAIN 2 will require the operators to stay in the same position throughout the course of each procedure, he explained.

But all of these studies, present and future, are meant to educate, Dr. Mahmud observed. “I am always shocked as to how few people seem to even admit that [radiation] is an issue. So I think it’s going to take more and more information, knowledge, and dissemination,” about the potential risk and any preventative options available, he said.

 

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Source: 
Reeves RR, Ang L, Bahadorani J, et al. Invasive cardiologists are exposed to greater left sided cranial radiation: the BRAIN study (Brain Radiation Exposure and Attenuation During Invasive Cardiology Procedures). J Am Coll Cardiol Intv. 2015;8:1197-1206.

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