The 15th Annual Warren K. Sinclair Keynote Address-Jus•ti•fied and Com•men•su•rate.

When patients are exposed to ionizing radiation for medical diagnosis or treatment, the procedure being performed should be justified, and the amount of ionizing radiation used should be commensurate with the medical purpose. A legal limit on the amount of ionizing radiation used for medical exposure of a patient does not apply. The biological basis for radiation protection of patients is the same as for all other ionizing radiation exposures: prevent or avoid tissue reactions and reduce the probability of stochastic effects (primarily cancer) while maintaining the benefits to the individual and to society. Justifying the clinical procedure as (1) being appropriate for the clinical purpose and (2) being appropriate for an individual patient is in the purview of the clinical community and individual practitioners, respectively. Managing ionizing radiation levels to be commensurate with the medical purpose is becoming a more prominent feature for all types of imaging procedures (to manage the increased probability of cancer). An approach using advisory diagnostic reference levels is finding widespread use throughout the world. A diagnostic reference level is a method for evaluating whether the amount of radiation is unusually high or low for a particular imaging procedure.