August 11th, 2013

Radiation Exposure in the Cath Lab: A Radioactive Topic?

In 2009, I published an article in the NEJM with my friend and mentor, Brahmajee Nallamothu, and several other colleagues. It documented rates of radiation exposure from medical imaging. As I worked on the paper, I learned that many clinicians, including radiologists, consider their training in this area to be inadequate, focusing more on technical intricacies than on identifying which patients are at greatest risk for exposure from ionizing radiation and on strategies to minimize that risk. Cardiovascular imaging, in particular, is responsible for a significant proportion of all medical radiation exposure, yet cardiologists are taught very little about it. So I have become interested in increasing awareness of radiation safety among clinicians in general and cardiologists specifically, especially interventionalists (I am about to start an interventional cardiology fellowship).

The good news is that awareness of radiation exposure from cardiac CT and nuclear imaging has increased in the past few years. The bad news is that the topic remains much less visible for fluoroscopic procedures. Until recently, the only available U.S. benchmark data for radiation doses in interventional cardiology procedures were derived from a Nationwide Evaluation of X-ray Trends (NEXT) survey, a study with a relatively small sample size (n=2407) that did not account for procedure complexity.

Our group has now used data from the CathPCI Registry to define determinants of fluoroscopy time for invasive cardiac angiography (ICA) and percutaneous coronary intervention (PCI). This study, published in Catheterization and Cardiovascular Interventions, describes the distributions of fluoroscopy times for ICA and PCI in more than 3 million procedures. Here are our key findings of interest to clinicians:

1. We described distributions of fluoroscopy time for each ICA and PCI — and also evaluated the incremental fluoroscopy time associated with important patient, procedure, operator, and hospital characteristics. This work finally gives catheterization labs a benchmark to assess how they are performing relative to a national, complexity-adjusted average.

2. Most of the variation in fluoroscopy time was related to “fixed” patient- and procedure-related factors. This sets a floor for how much improvement we can expect from quality efforts. However, about 20% of this variation was related to potentially modifiable operator and hospital-level factors. Not surprisingly, operator volume was inversely associated with fluoroscopy time for both ICA and PCI, as was being at a university hospital. These factors present some challenges, given the essential need to minimize patient harm while training the next generation of interventional cardiologists.

3. My interactions with fellow invasive cardiologists suggest to me that relatively few of them are familiar with the preferred dose metrics for fluoroscopic radiation exposure: (A) total air kerma at the reference point (a measure of peak skin dose); and (B) air kerma-area product (a measure of total radiation exposure and risk to the patient). It is not surprising, then, that interventionalists don’t routinely track these metrics during procedures, even though all fluoroscopy machines manufactured since 2006 display them in real time (to comply with FDA regulations). It is our hope that this paper will encourage operators to learn more about these metrics and to start routinely monitoring them during procedures.

I would like to invite fellow clinicians, especially interventional cardiologists and medical physicists, to read the paper and share their thoughts. In particular, we provide a table of techniques (reproduced below) that have been recommended by regulatory authorities. I’m curious to hear how often you observe these techniques being used in daily practice. I’ve come to realize that radiation exposure is a “silent danger” that is difficult for individual clinicians to quantify and address on their own.



Fluoroscopic Dose-Rate Management Techniques*
  • Keep the patient as close as reasonably possible to the image receptor and as far as possible from the x-ray tube.
  • Use collimation to reduce the irradiated area.
  • Use the lowest acceptable magnification.
  • Use the lowest clinically acceptable dose-rate at all times.
  • Use fluoroscopy only for real-time imaging guidance.
  • Use Image acquisition (Cine or DSA) only when higher-quality image review is essential.
  • Use last-image-hold or loop replay in place of live imaging whenever practicable. In some cases, retrospectively stored fluoroscopy may replace image acquisition.
  • Minimize the number of cine series.
  • Never use cine as a substitute for fluoroscopy.
  • Use wedge filters when they are appropriate.
  • Try to avoid steeply angulated projections (especially LAO cranial).
  • Try to vary the C-arm angulation slightly, to avoid concentrating the radiation dose at a single site on the patient‘s skin.
  • Remember that for large patients, and also for steeply angulated projections, the dose to the patient increases substantially.
  • Pay attention to the patient radiation dose display in the procedure room.
  • If the patient has had previous similar procedures, try to obtain information about the previous radiation doses to optimize subsequent procedures.

*adapted from NCRP-168 and ICRP Draft Report for Consultation on Patient and Staff Radiological Protection in Cardiology

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