The risk of not imaging: a three-scenario framework for justification.

A recurring argument in radiological protection holds that the radiation risk of an imaging examination must be weighed against the clinical risk of not performing it. The argument is applied inconsistently, and evidence on that clinical risk remains sparse compared with the extensive literature on radiation risk. This asymmetry masks an important distinction: the clinical risk of not imaging is not uniformly high. We propose a three-scenario framework for medical imaging, illustrated using computed tomography. In Scenario 1, the harm of withholding or delaying imaging is well documented and substantially exceeds the radiation risk, as in appendicitis, stroke, pulmonary embolism, aortic dissection, and polytrauma. In Scenario 2, imaging is repeated at low incremental yield, exposure accumulates, and guidance on intervals is limited, so radiation risk may outweigh marginal diagnostic gain. In Scenario 3, evidence on both sides is insufficient, and decisions are best supported by clinical decision rules and shared decision making. The framework addresses procedure-level and individual justification, and is confined to the balance between clinical and radiation risk. We suggest that clinical specialty organizations develop guidance on imaging frequency that incorporates review of cumulative exposure, and that ICRP address the place of such exposure within the justification framework.