November 30, 2009

Interventional Update
Alternative Guidance Systems Minimize X-Ray Exposure

By Steve Wagner
Radiology Today
Vol. 10 No. 19 P. 32

For years, physicians have wrestled with a well-known dilemma: how to avoid the risks posed by the radiation they use to ensure pinpoint accuracy in the operating room and interventional suite.

Many ignore contact with the fluoroscopy beam, looking the other way and hoping for the best. Others wear lead aprons that leave the thyroid area, eyes, and hands exposed. A few cover themselves from head to toe.

To spread the word that radiation can have long-term implications, such as blood-borne cancers, other forms of the disease, and cataracts, Isador Lieberman, MD, chairman of the Medical, Interventional and Surgical Spine Care Center at the Cleveland Clinic Florida, has emerged as a champion of sorts. It’s a cause he believes in.

“All surgical specialists have been using some form of intraoperative or procedural x-rays to help us visualize anatomy, position our instruments, and find pathology,” he says, adding, “We have to make sure that everyone understands the issues of radiation.”

Fluoroscopy Use
The issue involves the use of fluoroscopy to obtain real-time images that guide physicians during procedures. Interventional radiologists and general, spine, orthopedic, vascular, gynecologic, and otolaryngology surgeons all use x-ray–based technology in the operating room.

By using the technology, they’re achieving better accuracy than ever before—and leaving themselves open to various forms of cancer and other conditions known to develop after years of radiation exposure.

“We need real-time, accurate imaging,” Lieberman says. “We need to know where the tip of the instrument is in three-dimensional space every time we move it. That requires a new x-ray with each step of the procedure.”

In fact, vascular procedures can require up to 30 minutes of fluoro time, while other procedures demand far less—although still too much, Lieberman says. The result is considerable exposure to the hands, eyes, thyroid, overall body, and perhaps even the brain over prolonged periods.

During the past five to 10 years, as image-guided procedures have proliferated, an increasing number of physicians have begun using lead aprons to protect themselves. That has helped, but the problem has only diminished and not been eliminated.

“I must admit, and I’m guilty of it myself, surgeons get lazy. We’re always in a rush, we put the apron on carelessly, we forget to put a thyroid shield on, and we turn our backs to the x-ray machine. With some of the older gowns, there’s clearly no lead on our backs,” Lieberman says. “And some gowns are so old that they have cracks in them, and the radiation protection is not up to par.”

Protections
Increasingly, cataracts have begun developing in physicians after years of radiation exposure. As a result, some have begun wearing lead-lined glasses.

“The first line of protection is to keep yourself out of the beam,” Lieberman says. “The second line of protection is to keep yourself 6 feet away from the beam. The third line of protection is to wear lead glasses, a thyroid shield, and an apron.”

Lieberman concedes that effects on the brain with respect to radiation are less well known, and that many surgeons draw the line at wearing gloves that inhibit the tactile feedback they require. Besides, the x-ray beam as it strikes the gloves can transmit low-level radiation directly into the hands, negating much of the protection they promise.
Recently, a fourth line of protection has emerged: navigation techniques that utilize alternate forms of energy. These include infrared, magnetic, ultrasound, and robotic navigation. In many cases, they require only a reference x-ray at the beginning of a procedure and a second image toward the conclusion.

Reducing Exposure
Most common is infrared, where sensors on rigid surgical tools are detected by infrared scanners placed around the operating room. With the patient serving as the reference point in 3D space, the computer guides surgeons with pinpoint accuracy.

Of growing interest is magnetic navigation. Here, motion trackers measure the position and orientation of sensors in 3D space. Measurements are then used to track the tips of flexible medical instruments and devices in order to localize and target.

Ascension Technology Corporation offers its medSAFE, driveBAY, and trakSTAR tracking technology systems that utilize miniaturized magnetic sensors in combination with imaging systems that let clinicians follow real-time graphic displays of current and projected interventional tool positions on either real-time ultrasound or reconstructed CT, MR, or PET images. As a result, clinicians can quickly and precisely guide biopsy needles and ablation or other tools to soft tissue lesions with minimal risk of damaging adjacent anatomy.

Ascension Technology’s magnetically guided intervention line utilizes previsualization of target trajectory and single-needle insertion to shorten procedures. When used with CT imaging, the number of verification CT scans is reduced, minimizing exposure. Also with CT, an additional position/orientation measurement sensor is placed on the patient, so the true anatomical position of the target can be continuously monitored during a procedure.

While non–x-ray navigation tools are still catching on, magnetic technology offers advantages. Accuracy is comparable to that achieved using fluoroscopy, and radiation exposure can be greatly reduced or even eliminated—a benefit to both patients and physicians.

Radiologists, who are educated about the risk, better understand what they face and the precautions they must take each day, but other physicians using imaging are not as well trained.

“I’d say that 80% to 90% of surgeons don’t fully understand the risk,” Lieberman says. “I hammer on the issue with the residents and fellows who work with me. I ask them, ‘Do you want to have three-headed children?’”

 While that’s an exaggeration, physicians are clearly being affected by radiation exposure as they age. One surgical mentor to Lieberman has developed thyroid cancer, prostate cancer, and cataracts.

“These new technologies can make a good physician better,” he says. “And they can protect everyone in the operating room, including the patient, from receiving unnecessary radiation. In the long run, it can help prevent some of these catastrophic conditions and even save lives.”