Cheryl Proval

From its earliest days to the present, radiation has been very much with the radiology profession. And while there are radiological procedures that do not require patient exposure to ionizing radiation, they are defined as much by its absence as the radiograph is by its presence. Radiation remains radiology’s sine qua non.

The issue of radiation exposure, however, has not had the resonance here that it has in Europe, where the public, physicians, and even radiologists are far more attuned to dose than their American counterparts. Dose, nevertheless, has arrived on the American radar screen, delivered by three relatively recent developments:

1) Two studies 1,2 were published earlier this year, and one determined that pediatric patients were receiving a higher dose than necessary when undergoing whole body helical CT.

2) Self-referred whole-body CT screening. There is without a doubt a keen public interest in this procedure. Theoretically, a medical decision to expose a patient to ionizing radiation is made only if the information to be gained supercedes in importance the dose’s potentially deleterious effects. When a patient self refers, is it the responsibility of the facility offering the procedure to present a disclosure on the risks of radiation exposure?

3) The FDA meeting. In May, the oldest standing Food and Drug Advisory committee, the Technical Electronic Product Radiation Safety Standards Committee (TEPRSSC), met to discuss, among other topics, the challenge of monitoring the dose patients may receive from? computed tomography (CT) scanners. The issue of monitoring dose has been debated by TEPRSSC for close to 10 years, according to Orhan Suleiman, PhD, TEPRSSC executive secretary. In fact, the committee will soon publish proposed standards for fluoroscopy equipment that, if implemented, will mandate the display of cumulative radiation dose and dose rate on every piece of fluoroscopy equipment sold in the US.

But devising a metric for obtaining dose delivered for fluoroscopy’s two-dimensional images is fairly straightforward; designing a metric for calculating helical CT dose is elusive precisely because the technology is so sophisticated, Suleiman says. “For CT you have a very complex geometry: the beam is a fan beam and not uniform,” he notes. “Usually they employ a bow tie filter; and it is not a two-dimensional application, because now we are rotating it around the patient. So calculating how much radiation all of the organs receive is much more complicated.”

While the committee discussed the idea of requiring dose display for CT scanners, it first must solve the puzzle of developing an adequate standard. The International Electrotechnical Commission (IEC) did generate recently a standard for CT dose display, mandatory for scanners sold within the European Union. However the standard is not considered by some physicists to be rigorously described. It is currently under review by IEC, according to Suleiman. “The IEC deserves credit for taking the lead, but now they are getting flak because they did not do it right,” he says. “The articles [in the AJR] were enough to get the issue on the table because the standard that did exist was not adequate.”

The next step is for the FDA to convene an internal committee to work on a standard. “Once standard dose metrics are developed, then you can make an intelligent decision on how much radiation is necessary for the clinical examination,” Suleiman says. “We are not talking about regulating dose, we are talking about displaying dose.”

Now that the issue has arrived, it must not be merely tolerated. Radiologists and their administrators must be prepared to take a proactive role in this discussion with government, with patients, and with each other in order to maintain responsible stewardship of the remarkable source of energy that has revolutionized diagnosis and intervention in medicine.

Cheryl Proval

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  1. Paterson A,Frush DP, Donnelly LF. Helical CT of the body: are settings adjusted for pediatric patients? AJR 2001;176:297-301.
  2. Brenner DJ, Elliston CD, Hall EJ, Berdon WE. Estimated risks of radiation-induced fatal cancer from pediatric CT. AJR 2001;176:289-296.