Reducing radiation exposure

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– “It’s surprising to me today, when I go proctor or watch a case, how people don’t understand the impact of radiation,” Dr. Mark A. Farber, professor of surgery and radiology at the University of North Carolina, Chapel Hill, said at the Southern Association for Vascular Surgery annual meeting. “Many times, I see people’s hands underneath the machine and on the fluoroscopy image.”

This flouting of the so-called ALARA (as low as reasonably achievable) principle happens in part because the number of complex procedures performed by vascular surgeons is increasing, despite what presenter Dr. Melissa Kirkwood, a vascular surgeon at the University of Texas Southwestern Medical Center, Dallas, told the audience is a lack of training in radiation dose terminology and basic safety principles. Yet, practicing excellent radiation safety protocols is “paramount” according to Dr. Farber who, along with Dr. Kirkwood, shared insights on how to minimize dose to both patients and vascular specialists, whether it be from primary, leakage, or scatter radiation.

Dr. Melissa Kirkwood

Dr. Melissa Kirkwood

Table up, detector down

Minimizing the air gap by as little as 100 mm – from 700 mm to 600 mm, for example – can reduce the dose of radiation from 17%-29%, whereas a 
10-cm increase in the air gap can result in as much as a 20%-38% increase in the radiation skin dose. This is essentially the application of the inverse square law, according to Dr. Kirkwood.

Dr. Farber said that some of the newer, more advanced machines have sensors that automatically detect where the collector should be in relation to the patient, but if your machine doesn’t have these “bells and whistles … remember that the skin dose decreases as the air gap decreases.”

 

Dr. Mark A. Farber

Dr. Mark A. Farber

Slow the frame rate

Another advantage to using new imaging systems, according to Dr. Farber, is that they allow the use of pulsed fluoroscopy for as few as 2 or 3 pulses/sec. The selected pulse rate determines the number of fluoroscopic image frames that are generated by the machine per second. This is significant when the dose savings are essential and when performing simpler procedures, he said. “If you go from 7.5 frames down to 3 frames/sec, you can decrease the exposure for both you and your patient.”

Use between 15 and 30 pulses/sec for critical procedures where precision is crucial, but reducing the rate to 7.5 pulses/sec may result in as much as 70% less of a skin dose.

Add radiation barriers

Don’t assume that the lead shielding is doing the job. “It’s important that you keep up on this and have it tested regularly,” said Dr. Farber, who recently discovered his thyroid shield was cracked and needed to be replaced. Also, consider the lead shielding of your staff, which, even if it is not used as frequently as the physician’s, can suffer from improper handling. “They fold it or crinkle it up and drop it on the floor. This can lead to problems,” he said. And be sure to remember leaded glasses, lead drapes for the sides of the table, and leaded ceiling-mounted or standing shields.

For extra protection, Dr. Farber recommended the use of disposable protective drapes with cut-outs that allow access to the patient while helping to reduce the amount of scatter radiation exposure to the operator’s limbs. At a tally of anywhere from 1 to 10 mGy/hour, scatter radiation emanating from the patient is a particular risk to the operator’s legs from the knees down, said Dr. Kirkwood, “depending on how tall you are.”

Using the disposable drapes also can result in a 12-fold decrease in the amount of scatter on the eyes, a 25-fold decrease in thyroid exposure to scatter, and a 29-fold decrease in the hands being exposed. “They can be cumbersome at times, I admit,” Dr. Farber said. “But there is no substitute for using protective drapes.”

Leaded aprons also help cut radiation transmission rates, even if they are not foolproof. Wearing two-piece leaded apron systems can help cut down the body strain from the weight of the aprons; however, Dr. Farber said that, at his institution, they use a suspended body shield system operated by a boom so there is no physical stress on the clinician. Because the weightless system also provides additional protection for the specialist’s head and limbs, Dr. Farber said that the hefty price tag is justified. “The way I sold it to the hospital was I told them I could stop doing procedures, or they could get me one of these systems so I could do more procedures,” he said, adding he is having a weightless system installed on each side of the table. “They’ll get their money’s worth by the fact that you’re not over your exposure limit.”

And finally, don’t forget to protect the anesthesiologist! A standing shield that gives broad coverage area should suffice, Dr. Farber said.

Alter the intensifier position

Altering the angle can help ensure that one area of the patient’s body isn’t being overexposed to radiation. Since previously irradiated skin reacts abnormally when re-exposed to radiation because the regeneration and repair of the dermis can take up to several weeks after the initial insult, the timing of the intervals between exposures is critical, said Dr. Kirkwood, adding that the Joint Commission recommended that all doses of fluoroscopically guided interventions performed within the past 6-12 months should be considered when assessing potential skin injury risk.

Use collimation

Making it tighter, for example, can help improve image quality and reduce the radiation dose to both the patient and the operator, as can varying the acquisition rates.

Exit the room during DSA

During digital subtraction angiography, Dr. Farber said to “get away from the table if you can! It’s a huge dose you don’t need to be exposed to if you don’t need to be right next to the machine.” Dr. Kirkwood agreed: “Angiography is 10-100 times more dose than fluoroscopy.”

Reduce magnification

Using a larger monitor allows the operator to see more detail without increasing the magnification, which also increases the dose in the amount of the diameter over the diameter squared. “By not magnifying up [from a field of view of 14 to 28], you will save yourself a factor of at least 4,” Dr. Farber said. “And the actual dose may be even less.”

Optimize imaging

Today’s advanced imaging systems make it easy to produce many high-quality images – CT scans and ultrasounds – that allow a more comprehensive picture. Having various image sources on screen at once is “practice changing” because it can help clinicians see more possibilities for “how to do the case,” said Dr. Farber. “I’ve never heard anyone say, ’Well, I wish I didn’t have that extra imaging next to me.’ ”

Save images

But once you get it, don’t forget to keep it. “Many times you do an acquisition, you move the machine, and you realize you forget to save the image and now you’ve got to go back and do it all over again,” Dr. Farber lamented. But by once again making technology your friend, with functions that allow auto-return to previous positions, among other auto-commands, you can save the needed information and reduce any unnecessary dose exposure for both yourself and the patient, he said.

Protect your eyes

Cataracts are still all too common in the field, according to Dr. Farber. “It’s important that you have side shields on your glasses to cut down on the amount of radiation that comes in and around the glasses.” Eschew glasses that don’t overtly hug your face.

Geometric differences

Don’t forget that, if you’re standing on the side of the imaging source, the scattering effect will be greater than if you’re on the side of the image receptor. Once again, an understanding of the inverse square law can be protective, according to Dr. Kirkwood: “As x-rays exit the source, there is an exponential decrease in the number of x-rays per unit area as the distance from the source increases.”

“It’s simple stuff,” concluded Dr. Farber. “If you get in the habit of doing these things you will cut down your radiation exposure.”

Neither Dr. Farber nor Dr. Kirkwood had any relevant disclosures.

wmcknight@frontlinemedcom.com
On Twitter @whitneymcknight

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