Justify, then examine
A request is not a reason.
The scan that should not happen
Patients have no dose limit. What protects them is the decision not to expose them without a reason.
How we work
Why justification comes before technique
Protection against ionising radiation is built differently for patients than for anyone else. A worker and a member of the public are protected by dose limits: a ceiling, fixed in advance, which must not be exceeded. No such limit applies to a patient undergoing a medical exposure, and the reason is not carelessness. A ceiling would occasionally stand between a patient and an examination they genuinely needed, which is precisely the situation in which exposure is warranted. So the protection is moved earlier in the process, into two principles applied before and during every exposure.
The first is justification, and it governs whether the examination should take place at all. An exposure must show a sufficient net benefit for the individual concerned, weighed against the detriment it may cause, taking into account the availability and characteristics of alternative techniques that would answer the same clinical question with no exposure or a lower one. The practical consequence is the one patients find most difficult to accept: a request for a scan is not a justification for a scan. Agreeing to an unnecessary examination is not an act of courtesy. It is an exposure with nothing on the other side of the balance, and it carries the additional risk of producing an incidental finding that generates further investigation without ever answering a question anyone needed answered.
The second is optimisation, and it governs how. Once an examination is justified, the dose is kept as low as reasonably achievable consistent with obtaining the diagnostic information required, which cuts both ways: a dose too low to produce an interpretable image is an exposure for nothing at all. Around these sit the practical obligations, authorisation from the federal nuclear control authority for the use of sources, the involvement of a medical physics expert where required, and the need for a patient to say before an examination whether she is or might be pregnant. One distinction is worth repeating because it is confused so often: ultrasound uses no ionising radiation, and nothing in this framework applies to it in the same way.
Our principles
Three beliefs behind the method
As low as achievable
But high enough to read.
Explain the result
Context, not a number.
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