UNC Cardiac Catheterization Lab reduces average radiation dose to physicians and staff by 25 percent

When technologist Mike Wolter, RT, moved from Vascular Interventional Radiology (VIR) to the Cardiac Catheterization Lab in the fall of 2012, he was reviewing radiation doses in the lab and wondered if a small reduction in the frame rate would make a difference in the long-term total radiation dose to which the cath lab employees were exposed. Here's what he found.

There are many medical reasons for needing an x-ray: broken bones, trauma to an internal organ, cancer diagnosis and treatment. The list goes on and on. During each of these x-rays, the patient is exposed to radiation.

Treatment in the cardiac catheterization lab is no different. During a typical procedure, a patient is brought into the procedure room and assisted onto a procedure table, x-ray scanning is performed to guide the physician and technologists during the procedure, and then the patient is transferred from the procedure table and taken to a room to recover.

However, the physicians and technologists do not leave the lab after one patient. They are in the lab all day, all week, all month, for many, many years. They are exposed to more radiation than any single patient will probably receive in their lifetime.

How do we keep these dedicated health care workers safe from radiation exposure?

The UNC Cardiac Catheterization Lab and Electrophysiology Lab have always been highly aware of radiation safety for its workers, and have maintained excellent radiation levels throughout the years, always much lower than the regulatory dose limit in the United States. 

Over the past year, small changes have been made in the Cardiac Catheterization lab, which is on track to reduce the average dose of radiation to physicians and staff by 25 percent in 2013, as compared to the previous four years.

When technologist Mike Wolter, RT (pictured on right), moved from Vascular Interventional Radiology (VIR) to the Cardiac Catheterization Lab Mike Wolterin the fall of 2012, he was reviewing radiation doses in the lab and wondered if a small reduction in the frame rate would make a difference in the long-term total radiation dose to which the cath lab employees were exposed. Also, would it make a difference in the image quality that the physicians needed to treat the patients? Could he lower the frame rate AND achieve a useable image?

Having worked in VIR for many years, and having learned a great deal about radiation safety from VIR physician Robert Dixon, MD, Wolter decided to make some small changes in the cath lab. 

The frame rate is the number of x-ray frames per second needed to view images of a moving object in real time. For example, when x-rays are performed to assess a broken bone, the bone is completely still with no movement involved. In the cath lab, the x-rays are assessing moving organs: the heart, kidneys, blood vessels, etc. Thus, an x-ray in the cath lab must take multiple frames per second to accurately show the moving organ/vessel.

Fluoroscopy is the medical term for the type of imaging that shows a continuous x-ray image on a monitor, which is what is used in the UNC cath lab. During a fluoroscopy procedure, an x-ray beam is passed through the body. The image is transmitted to a monitor so the movement of a body part, medical instrument or contrast agent in the body, like x-ray dye, can be seen in detail.

Wolter says, “Everybody focuses on fluoro-time (the actual length of time in which the patient is exposed to an x-ray beam).  However, it isn’t a direct representation of how much x-ray is being used. Of course, we want to cut down on fluoro-time, but I was taught to look at total patient dose during a procedure.”

Wolter started by suggesting a few things here and there and putting in his own settings for the patient frame rate, checking constantly to confirm that the physicians were able to use the images provided by the reduced frame rate. By reducing the number of frames per second, less radiation is produced.

Bradford Taylor, Associate Radiation Safety Officer for UNC Environment, Health & Safety, stresses that the goal with radiation is to use “the lowest amount to give an acceptable, diagnostic image.”

Taylor’s job is to make sure that employees at UNC are exposed to as little radiation as possible, making sure that they meet federal guidelines for radiation exposure as well as the guidelines mandated by the UNC School of Medicine and UNC Health Care.

The U.S. regulatory dose limit for radiation is 5,000 millirem/year (50 mSv/year). The average background radiation received by Americans each year is about 600 millirem (6 mSv), coming from a variety of natural sources (radon and thoron) and man-made sources such as consumer products, nuclear medicine procedures, and, of course, medical x-ray systems. 

From 2009-2012, the physicians in the UNC cath lab received an average annual radiation dose of 579 millirem. The technologists and staff in the cath lab received an average annual dose 172 millirem. Physicians, technologists and staff wear dosimeter badges that measure the radiation they are exposed to each day, and the badges are collected monthly.

Taylor has some helpful tips to remember when discussing radiation exposure.

Physicians will (most likely) always have higher doses.

Taylor explains, “Physicians get the highest dose. End of story. The procedures require them to be located closest to the patient where the doses are highest.” 

The farther a person is from a radiation source, the less they absorb. Technologists have more flexibility than the physician to step back from the radiation source during a procedure, and the distance does not need to be large to make a difference. Doubling the distance between a person and a radiation source reduces the radiation by a factor of four. If a technologist is 12 inches from the radiation source, and steps back an extra 12 inches, their dose will be four times less.

Always find out what dose calculation is being used.

Taylor says, “There are two standard measurements in dose reading: DDE and EDE. DDE is the deep dose reading of radiation. This is the exact reading from the dosimeter badges, which do not take into account any protection offered by the lead apron. EDE is the effective dose reading of radiation. This number is closer to the actual amount of absorbed radiation as it takes into account lead shielding.”

The UNC cath lab average annual dose of 579 millirem and 172 millirem from 2009-2012 is the DDE dose reading. By applying the EDE equation, which takes into account lead shielding, the average annual dose for UNC physicians and technologists/staff in the cath lab drops to 174 millirem and 52 millirem, respectively.

Don’t jump to conclusions when learning about increases or decreases in radiation exposure

Taylor recommends caution when reading about radiation exposure in the media or other sources. He says, “There are many factors that must be considered when evaluating radiation exposure. You need to find out the dose calculation being used (DDE vs. EDE). You also need to know the number of cases per year that are being performed. If volume is increasing in a particular lab, then that could be one reason why radiation is increasing."

He adds, “The opposite could also be true. If a decrease in the average dose of radiation is discovered, it could be simply that fewer procedures are being performed.”

Of the procedural cost centers reviewed in the UNC cath lab from 2009-2012:

  • 47% of procedures had an increase in total volume
  • 25% of procedures had a decrease in total volume
  • 28% of procedures had the same total volume

If this growth trend continues while the total radiation dose is being decreased, it is quite an accomplishment for the UNC Cath lab.

Best Practices in the UNC Cardiac Catheterization Lab

Since Wolter began reducing the patient x-ray frame rate in the Cath lab, the physicians and other technologists have agreed that it was a good decision, with everyone taking an active role to continually improve radiation safety.

Wolter explains, “Sometimes, the frame rate is increased to where it was previously, and the physicians will say, ‘That’s just too fast.’ They’ve adjusted to the lower frame rate very well with excellent patient results.”

Every physician and technologist wears a lead apron, which is very effective in protecting workers from up to 90% of the radiation to which they are exposed. Many also wear lead around their neck to protect their thyroid and other sensitive areas in the neck.

Wolter also decided to add some extra lead shielding in the procedure rooms. He added a second lead drape to protect the chest, in addition to lead shielding below the patient table to protect the legs and feet of the physicians and technologists.

no lead for legsyes lead for legsno abdomen shieldyes abdomen shield

Pictured from left: Cath Lab procedure table without the second lead drape protecting the legs; Cath Lab procedure table with the additional lead drape in place (notice the large gap is now sealed off); Cath Lab table without the lead chest shield; Cath Lab table with the additional lead chest shield in place, which adds 12-15 more inches of vertical protection.

In the first three months that Wolter implemented these changes (4thquarter 2012), the average radiation dose dropped by 35%. The fourth quarter 2013 radiation dose levels are still being processed, but if these trends continue, the Cath lab will have ended 2013 with a 25 percent yearly reduction in the average dose of radiation for physicians, technologists and staff.

Wolter says, “If we want to have successful, lifetime careers treating patients in a cardiac catheterization lab setting, we need to be vigilant about making it safe for everyone.”