SCOTTSDALE, ARIZ. – “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 and on the fluoroscopy machine.”
This flouting of the so-called ALARA principle (as low as reasonably achievable) 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 principals.
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.
Table up, top 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% to 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.
Although 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, he cautioned that, if your machine doesn’t have these “bells and whistles … remember that the skin dose decreases as the air gap decreases.”
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 or for 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 is as much as 70% less of a skin dose.
Don’t just 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.
Additionally, 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 can be no substitute for using protective drapes.”
Leaded aprons also can 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 now 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 (approximately $50,000) 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 has had 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.”