ALARP: when does reasonably practicable become rather pricey?

The Ionising Radiations Regulations 2017 require employers to restrict radiation doses to their employees and the public to be As Low As Reasonably Practicable. This article looks at the boundary between what might be considered to be reasonable and unreasonable in protecting staff and the general public in the field of hospital-based diagnostic radiology. A simple test for locating this boundary based on a cost–benefit approach is devised and its use illustrated using hospital-based radiation protection examples. It is concluded that a cost–benefit calculation based on the legal definition of As Low As Reasonably Practicable may have some use in the support of radiation protection decision-making in the hospital environment, but only within the context of existing legal, practical and ethical considerations.