The 'Justification and Optimization" principles are part of the European directives included in the regulations of the Union member countries. These two radiological protection principles play an important role especially in the medical field responsible today for 98% of exposures to non-natural sources of radiation.
These principles intervene also in industry where radioactive techniques should be used only if they provide a benefit over other methods. In the nuclear industry, optimization has reduced exposures to radioactivity to the point that it represents only 1-2% of the medical exposures. It is at the origin of even more dramatic advances in radiological protection of staff exposed to radioactivity.
In medicine, justification consists to irradiate only if really useful information can be expected for the care of the patient. For example, one would prefer a not irradiating Magnetic resonance imaging (MRI ) to a scanner (X-ray computed tomography) every time the scanner does not provide an added benefit.
When radiation is used in medicine, optimization means that one should irradiate with the maximum efficiency, while minimizing the intensity of radiation and the dose received.
Given the little knowledge we have about the effects of low doses, one should avoid to overlook eventual effects. One should avoid, in the opposite direction, the trap of an excessive fear of radiation which could be detrimental to medical diagnosis and cares : Any dose as low to one millisievert or one tenth of a millisievert does not present a serious risk for a patient.
The justification and optimization rules required by European directives are justified by the fact that it is not possible to exclude an effect of low doses. However, some radioprotection experts believe that low dose effects may be much smaller than those assumed by the regulations which are based on the "linear no threshold" rule, in which case the dose limits, would actually be very conservative.
The younger a person is, the more justification and optimization are necessary. A 10 millisieverts dose for a 50 years old man is probably unimportant, but the same dose applied to a very young subject, especially to infants, may have consequences. This is shown for instance by the increase by a factor of 5 to 10 of the young children thyroid cancers risk, while the risk may be null beyond 20 or 30 years.
These examples of precautions to take for young children incline to command caution and common sense. The consequences of radiation exposure depends on many factors and one should be wary of oversimplifications and misleading generalizations.
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