Radiation protection is based on the three fundamental principles of justification of exposure, keeping doses as low as reasonably achievable (optimisation) and the application of dose limits. The International Commission on Radiological Protection (ICRP) is responsible for the development of these principles.
The justification principle is anecdotally known as the benefit vs. risk principle; that is, an individual's exposure to medical radiation should always have a greater benefit to the patient as to outweigh the negative consequences of the proposed examination. For example, the benefit in ordering a CT brain for a patient that has suffered significant head trauma outweighs any negative outcomes associated with that radiation exposure 1.
Optimisation is also known at the as low as reasonably achievable (ALARA) principle. That is, medical radiation exposures should always be kept as low as achievable to ensure it is employed optimally. There is a particular focus on the term achievable, as medical radiation exposure lower than achievable can result in non-diagnostic examinations 1.
Dose limits are recommended by the ICRP, they are in place to ensure that the individuals are not exposed to an unnecessarily high amount of ionising radiation. The limits are split into two groups, the public, and occupationally exposed workers. These limits do not apply to patients, however, the aforementioned principles do.
At the time of writing this article (April 2017) the dose limits recommended by the ICRP are as following:
- occupationally exposed workers limits
- an effective dose of 20 mSv a year, averaged over defined periods of 5 years with no single year > 50 mSv 1
- public exposure limits
- 1 mSv in a year
- 1. International Commission on Radiological Protection. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103, 2007.