Dose Reduction in the Interventional Suite Comes of Age
The increasing use of minimally-invasive surgical techniques performed with guidewires and catheters under fluoroscopic guidance has brought with it a renewed focus on radiation exposure. Vendors have designed cutting-edge technologies and software for fluoroscopy machines that help reduce dose. Hospitals and staff have instituted protocols to ensure that certain thresholds of fluoro time or dose are not breeched. And many facilities are working toward having patient dose exposure automatically uploaded to an EMR.
Health Imaging & IT spoke with a number of practitioners to see how they are implementing the latest dose-reduction technologies in their interventional suites.
Nuts and bolts
All modern fluoroscopy systems have sophisticated collimators and filters that help reduce radiation exposure. Collimators limit the beam, while filters raise its quality. In older models, as the image intensifier was moved away from the patient’s body, the amount of x-ray beams delivered to the body was the same. Even though the image was less sharp, the patient was still receiving the same high dose of radiation. Today’s models correct for that problem.
“Now, as you raise the image intensifier, the collimators automatically kick in and you are not irradiating the entire field of view,” says Linwood Williams, RT(R), unit director of the cath lab at Carilion Clinic in Roanoke, Va. Carilion has six cath labs, which are equipped with five fluoro units from Siemens Healthcare.
Copper filters, another tool to help reduce exposure, remove low-energy photons that do not thoroughly penetrate the body and, consequently, do not contribute to image quality. These low-energy x-ray beams also have a tendency to “scatter,” thereby hitting the cath lab staff as well.
Pulsed, rather than continuous, fluoroscopy is a standard dose reduction technique today, which cuts the radiation dose exposure by half. Each pulse can be calibrated to a certain dose (milli-Roentgen per minute, or mR/m). At the push of a button, the interventionalist can drop the dose by as much as one-half or as little as one-fourth. Frame rates also can be adjusted to save on radiation exposure. Coronary artery interventions generally need the finest image detail (25 to 30 frames per second), while some procedures, includ-ing many pediatric procedures, will be effective with a lower frame rate (from 1 to 15 frames/s). Variations in between include a lower frame rate with a higher calibrated mR/m or vice versa.
“You need to look at angiography procedures as fluid. At some point, you may need very little fine detail, but when you’re pushing out micro-coils for embolizing arteriovenous malformations, it’s critical to go up to a higher level,” says John Racadio, MD, division chief for interventional radiology at Cincinnati Children’s Hospital Medical Center in Ohio. Racadio makes use of three fluoro systems from Philips Healthcare.
The Q/A system at Cincinnati Children’s has what the technologists refer to as a “speeding ticket.” If a patient receives a skin dose greater than or equal to 2 Grays (Gy) or a cumulative dose greater than or equal to 3 Gy, a form (the “ticket”) must be completed that calls for a follow-up clinical exam in three weeks to look for signs such as temporary hair loss or skin problems.
“These types of symptoms manifest themselves at 3 gray,” Racadio says.
For now, the patient dose, which appears onscreen during the procedure, is recorded as part of the dictation, but the hospital is in the process of installing a new system (Epic) with the capability of automatically uploading patient dose data to the EMR.
At the Richard M. Ross Heart Hospital at the Ohio State Medical Center in Columbus, Ohio, radiation dose is recorded in the GE Healthcare Mac-Lab hemodynamic information system. Every 30 minutes, the staff takes a time out to check radiation exposure or contrast media dose amount, according to Linda Paxton, director of cardiovascular services. They then determine whether it’s safe to continue with the procedure, which depends on the patient’s weight and comorbidities, or whether the patient will have to return.
Racadio would like to see an IT system that records the radiation dose exposure from every procedure, including imaging, which would then become a part of the patient’s medical record.
“These patients will have many other medical imaging procedures that will increase the cumulative dose exposure. Unless someone is tracking them, no one knows how many multiple procedures or exams they’ve had,” he says.
Another problem, according to Racadio, is the unit measurement for dose exposure, which can vary from vendor to vendor. Not too long ago, he held a vendor summit at his facility, when the Image Gently campaign was rolled out. In attendance were representatives from industry, the FDA and the National Cancer Institute. Racadio expressed his desire to have a uniform agreed upon way to estimate dose so that it can be compared from one machine to another. This complaint, however, is not new, but maybe, Racadio says, “the time is right for a concerted action by all stakeholders to make it happen.”
The Image Gently campaign, spearheaded by the Alliance for Radiation Safety in Pediatric Imaging, was begun in 2008 with a focus on CT imaging. This year it expanded to include angiography with a “Step Lightly” (on the pedal) tagline. Currently, 13 societies representing the fields of radiology, pediatrics, and medical physics and radiation safety are involved. Racadio is a member of the writing committee.
The Web site (PedRad.org) offers resources for medical personnel as well as patients and their families. According to the site, interventional radiology procedures are the third largest contributor to medical radiation to the U.S. public, and children are particularly vulnerable. A downloadable procedure checklist includes tips such as:
- Ask patient or family about previous radiation;
- Position and collimate with fluoroscopy off, tapping on the pedal to check position;
- Minimize use of electronic magnification; use digital zoom whenever possible; and
- Use last image hold whenever possible instead of exposures.
Russel Hirsch, MD, a colleague of Racadio, is director of the cardiac catheterization laboratory at the Heart Institute at Cincinnati Children’s. He says it’s incumbent upon all medical staff, especially the operators, to learn all they can about reducing medical radiation exposure. “It’s good clinical practice, akin to washing your hands before a procedure.”
At Cincinnati Children’s, a radiation exposure safety subcommittee, mandated by the hospital board, has set conservative limits for the exposure that any one patient can receive during a procedure. Patient absorbed dose is expressed in terms of dose area product (DAP) per procedure (Gy cm2).
“When I get to the limit, less than 300 Gy cm2, I have a choice to make: either continue the procedure or stop,” Hirsch says. Since converting several years ago to a digital flat-panel unit, he has gone beyond the threshold only once. With the older film-based fluorosocopy system, the limit would be breeched an average of three times every two months.
At the Carilion Clinic, with the old 35-mm film camera, Williams, as a tech, would routinely absorb 200 millirad (mr) dose per month. When the switch to digital was made, that amount dropped to 110 mr per month.
“It takes a lot less radiation to have the digital image than the 35-mm film image,” Williams says.
Hirsch credits advances in technology for dramatically reducing the radiation exposure in the interventional suite. The first change was in the quality of the angiography. Rather than stepping on the pedal and having to search for the target, the quality of the image is now “so exceptional that you immediately see it, which saves on fluoro time.”