Diagnostic Reference Levels: Reducing Radiation Exposure Safe During X-Rays and CT Scans

Diagnostic reference levels (DRLs) are just one of the ways radiologists protect patients from excessive exposure to radiation during X-rays and CT scans, but most patients can go through a lifetime of imaging procedures without ever hearing of a DRL. If you’re worried about the ionizing radiation associated with some types of diagnostic imaging, though, you should know the basics of DRLs — starting with the knowledge that radiologists and technologists strive to expose patients to as little radiation as possible during every scan.

First, it’s important to understand what DRLs are not. They aren’t:

  • Legally binding radiation dose limits.
  • Measurements of the true radiation exposure to patients.
  • Indications of the exact amount of radiation a given patient absorbs.
  • Strict, one-size-fits-all guidelines.
  • Absolute upper limits for safe exposure.

So if they aren’t binding and they don’t actually determine the dose limit of radiation that patients can receive, how do DRLs help radiologists protect their patients? Lots of ways. To start with, DRLs provide a baseline measure of how much radiation a given scan creates. By establishing a standardized and easy-to-study standard of emission, they allow technologists to make sure equipment is functioning as it should. They also help imaging facilities compare one piece of scanning technology to another when they’re choosing new products.

Diagnostic reference levels shouldn’t be confused with dose limits, but they do help to reduce patient exposure to ionizing radiation nonetheless. If a given scan consistently exceeds the DRL as determined by regional or national medical organizations, radiologists know there’s either something wrong with the machine or they need to update their procedures.

DRLs also provide a “neutral” starting place for determining how much radiation is necessary to achieve clear images. Radiologists may start with a DRL and then dial the exposure back, or, if they need a better image, increase the radiation. A dose that’s higher than the regional DRL doesn’t indicate an unsafe procedure, and it doesn’t mean your radiologists is making a mistake. It just means that the scan needs a little bit more “juice” to produce the image that your doctors need to make a diagnosis and, ultimately, to treat your condition.

Where Do Diagnostic Reference Levels Come From?

The concept of the DRL first entered the practice of medicine in 1990. That’s when the International Commission on Radiological Protection (ICRP), an independent consortium of physicians, scientists, and policy makers dedicated to harm reduction in medical imaging, first suggested the use of radiation values that medical physicists and radiologists could use as an introductory standard against which to measure their own processes and equipment.

Maybe the ICRP’s 1996 statement, which further clarified DRLs, explains it better:

“The Commission now recommends the use of diagnostic reference levels for patients,” the report states, as quoted by Cynthia McCollough, PhD of the Mayo Clinic. “[T]he diagnostic reference level will be intended for use as a simple test for identifying situations where the level of patient dose or administered activity is unusually high.”

Ultimately, patients don’t need to understand the complexities of DRLs to know that their radiologists are working hard to keep them safe. The mere existence of this radiation benchmark, along with other technological and procedural safeguards, is a clear indication of the high level of care provided by today’s board-certified radiologic professionals. They aim to keep patients healthy, and diagnostic reference levels are just one way they work toward that goal.


Diagnostic reference levels in medical imaging: review and additional advice.PubMed. Annals of the ICRP, 2001. Web. 20 Nov. 2017.

McCollough, Cynthia. “Diagnostic Reference Levels.ImageWisely. American College of Radiology, n.d. Web. 20 Nov. 2017.

Radiological Protection in Medicine – ICRP Publication 105.ICRP. International Commission on Radiological Protection, 2007. Web. 20 Nov. 2017.