Working in an FDG production lab for around 20 years. Does the annual ICRP dose limit of 20mSv/Year avegraged over 5 years (and in a single year upto 50mSv) is following the ALARA principle.
Does this limit is in variable to the radioisotopes like 18F, 90Y, 177Lu, 99mTc etc following their nature of radiation and half life
Justification, optimization of protection (the ALARA principle, the best level of protection under the prevailing circumstances), and individual dose limitation (application of dose limits in planned exposure situation) are three fundamental principles of protection in the ICRP system of radiological protection (since the 1977 Recommendations in Publication 26). Dose constrains and reference levels are used in the process of optimization.
Dose limits (applicable in planned exposure situation) do not change by external or internal exposures, nor by radiation quality or radionuclides, although committed dose (over 50 years for exposure of adults) applies for internal exposures.
A limit is not ALARA. ALARA is practiced to hold doses below a limit. A dose limit should not be exceeded. There is no limit to dose reduction below a limit except reasonableness of reduction.
As Nobuyuki Hamada already pointed out, there are three separate principles of radiation protection: 1) Justification: deciding whether the benefits of the practice are worthy the radiation risk or not. 2) Optimization: mostly, applying ALARA. 3) Limitation: establishing hard limits that must not be exceded in planned exposures.
So, in other words, compliance with the dose limit is not equivalent at all with ALARA. The limit must be observed, and then the dose should be optimized further according to the ALARA principle. On the other and ALARA does not mean reducing dose to zero (which is impossible), but reducing it to the lowest reasonably achievable value.
To add to my esteemed colleagues, limits should not be exceeded nor should they be worked too. It is always good practice to apply a dose objective which is set below the limit, e.g. 2 mSv/year. This allows for the radiation safety professional to monitor and manage dose exposures to workers, the public and the environment, and to implement any measures to mitigate dose exposures. ALARA (and ALARP), is usually applied at the planning stage of any task that may lead to a potential increase in dose exposures above background, and is applied to ensure that all practical measures have been taken to minimise dose exposures, e.g. passive shielding or containment. It should also be applied periodically throughout the task process to ensure that ALARA principle continues to be met when comparing predicted against actual doses.
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