When a medical imaging exam provides a clinical benefit, the only risk that should be considered is the exam itself rather than a patient’s previous radiation exposure, according to a statement by three scientific groups representing medical physicists, radiologists, and health physicists.

The American Association of Physicists in Medicine (AAPM), in conjunction with the American College of Radiology (ACR) and the Health Physics Society (HPS), issued a joint statement in opposition to cumulative radiation dose limits for patient imaging, citing potential adverse effects on patient care. The statement comes in response to an opposing position by several organizations and recently published papers on the high-profile topic.

“It is the position of the AAPM, the ACR, and the HPS that the decision to perform a medical imaging exam should be based on clinical grounds, including the information available from prior imaging results, and not on the dose from prior imaging-related radiation exposures,” according to the statement.

Moreover, the statement reads, “AAPM has long advised, as recommended by the International Commission on Radiological Protection (ICRP), that justification of potential patient benefit and subsequent optimization of medical imaging exposures are the most appropriate actions to take to protect patients from unnecessary medical exposures. This is consistent with the foundational principles of radiation protection in medicine, namely that patient radiation dose limits are inappropriate for medical imaging exposures.

“Therefore, the AAPM recommends against using dose values, including effective dose, from a patient’s prior imaging exams for the purposes of medical decision-making. Using quantities such as cumulative effective dose may, unintentionally or by institutional or regulatory policy, negatively impact medical decisions and patient care.

“This position statement applies to the use of metrics to longitudinally track a patient’s dose from medical radiation exposures and infer potential stochastic risk from them. It does not apply to the use of organ-specific doses for purposes of evaluating the onset of deterministic effects (e.g., absorbed dose to the eye lens or skin) or performing epidemiological research.”

In addition to the three signatories, the Radiological Society of North America endorses the position. Further, the AAPM emphasizes the importance of patient safety in their position. The use of radiation must be both justified and optimized and should always offer a potential benefit to the patient that is greater than its potential risk.

“This statement is an important reminder that patients may receive substantial clinical benefit from imaging exams,” says James Dobbins, AAPM’s president. “While we want to see prudent use of radiation in medical imaging, and many of our scientific members are working on means of reducing overall patient radiation dose, we believe it is an important matter of patient safety and clinical care that decisions on the use of imaging exams be made solely on the presenting clinical need and not on prior radiation dose.

AAPM cites the International Commission on Radiological Protection, which stresses that setting radiation exposure limits to patients is not appropriate. This is partially due to a lack of uniformity in metrics for monitoring dosages, and points to a need for standardizing dose estimates.  

The position only addresses stochastic risks from radiation exposure, which are chance effects whose risk for a given imaging exam, like cancer, is unrelated to the amount of prior radiation. Deterministic effects, which are incremental and a direct response to the exposure, such as skin damage, are a result of a different set of biological mechanisms and are not included.

Finally, the AAPM compiled a list of answers to frequently asked questions on the topic of medical radiation safety and a list of references to research papers supporting the organization’s position.