MEDPAGE TODAY ®
Radiation Exposure in Cath Lab Depends on Shield Placement
by Chris Kaiser
Cardiology Editor, MedPage Today October 17, 2011
This article is a collaboration between MedPage Today® and:
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Interventional cardiologists are at greatest risk of scatter radiation exposure compared with other personnel in the cath lab, but their risk can be significantly reduced with the optimal placement of radiation shielding, researchers found.
A ceiling-mounted upper body shield protected best from scatter radiation when it was positioned tight to the patient’s body and just toward the head from the femoral access point, reported Kenneth A. Fetterly, PhD, from the Mayo Clinic in Rochester, Minn., and colleagues.
However, a difference of 5 cm away from the patient’s body and 20 cm closer to the x ray tube resulted in a fourfold reduction in protection, according to the study in Oct. 25 Journal of the American College of Cardiology: Cardiovascular Interventions.
“That the most advantageous shield positioning can have a greater than fourfold relative reduction in scatter radiation exposure, supports its use even when inconvenient, and suggests that learning to coordinate multiple shields should be among the fundamental principles taught in every interventional cardiology training program,” wrote Lloyd W. Klein, MD, and Justin Maroney, MD, from Advocate Illinois Masonic Medical Center in Chicago, in an accompanying editorial.
Klein and Maroney noted that the design of the interventional suite has remained stagnant over the past few decades even as innovations in techniques and devices have soared. And because optimal placement of shielding “continues to be operator dependent,” it requires a deliberate effort on the part of cath lab personnel to place shield s.
To determine how best to protect against scatter radiation, which occurs when the primary x-ray beam interacts with patient tissue and changes direction, investigators tested four different shielding models individually and in com binat ion:
- A ceiling-mounted upper body shield
- A table side rail-mounted lower body shield
- An accessory vertical shield that mounts as an upper extension of the lower body shield
- A disposable radiation-absorbing pad
Researchers used anthropomorphic phantoms through which they directed the x-ray beam in a straight posterior-anterior posit ion.
They measured the scatter radiation from three common physician positions corresponding to standard right femoral art ery, right jugular vein, and left anterior thoracic access point s.
Results showed that maximum protection was provided at the femoral artery access position compared with the other two access points.
When the ceiling-mounted upper body shield was moved away from the patient’s body by 5 cm, and moved more cephalad from the femoral access point by 20 cm, the protective benefit to the middle and upper body went from greater than 80% to less than 20%.
The accessory vertical extension to the lower body shield provided between 25% and 90% additional protection at heights in the range of 100 cm to 150 cm. The disposable pad also provided extra upper body protection, in the range of 55% to 70%.
Researchers found that the combined use of the table apron with vertical extension and the upper body shield resulted in “at least 80% protection at all elevations and 90% protection for elevations below 150 cm” at the femoral access point.
Regarding protection from the right jugular vein and left anterior thoracic access points, testing showed that the lower body shield provided better than 90% reduction in scatter exposure, but no upper body protection, while the disposable pad provided lower body protection and only modest upper body protection (between 40% to 70%).
The upper body shield also interfered with the x-ray receptor and patient access when the right jugular vein access point was used, and it interfered with patient access from the anterior thoracic access point. Patient interference was common with the vertical extension as well.
“A major finding of this work is that the upper body protection provided by the ceiling mounted upper body shield is highly dependent on precise positioning,” researchers wrote.
“Note that conventional wisdom is that shields should be placed close to the source of radiation to maximize the size of the protective ‘radiation shadow’ of the shield. Properly positioning the upper body shield requires the opposite mindset,” Fetterly and colleagues said.
Klein and Maroney echoed this sentiment, saying the shield should be used “as one would use an umbrella in wind-driven rain: the closer to the operator’s body the more eff ect ive.”
Limitations of the study included the use of only the posterior-anterior projections, and the lack of an analysis of radiation scatter when involved with the treatment of abdominal and peripheral vessels.
The study authors and the editorialists reported relationships relevant to the contents of the study or editorial.
Reviewed by Zalman S. Agus, MD Em er itus Professor
University of Pennsylvania School of Medicine and Dorothy Caputo, MA, RN , BC-ADM, CDE, Nurse Planner
JACC: Cardiovascular Interventions
Source Reference: Fetterly, KA et al “Effective use of radiation shields to minimize operator dose during invasive cardiology procedures” J Am Coll Cardiol Intv 2011; 4: 1133-1139.
JACC: Cardiovascular Interventions
Source Reference : Klein LW, et al “Optimizing operator protection by proper radiation shield positioning in the interventional cardiology suite” J Am Coll Cardiol Intv 2011;4:1140-1141.
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