Shielding design goals are used in the design or evaluation of barriers constructed for the protection of patients, staff and the general public.
The shielding design goals are not procedure specific. They are related to the dose limits set by the regulatory bodies. For instance, the limit for professionally exposed staff is 20 mSv/y and the institution ususally chooses a lower limit - in Romania either 6 or 7 mSv/year. Similarly, the dose limit for the public will be 1 mSv/year. The shielding will be designed with these goals in mind and taking into consideration the equipment (output in Gy/week), the occupancy factors and the target doses (the reference levels).
For the patients, however, the situation is reversed: there are no dose limits because this would be a limitation to the medical act but there are reference dose levels specific to each kind of examination / procedure - but these refer to the doses received during the investigation and are not affected by the shielding. Once the patients leave the examination room, they are treated like any other member of the public with respect to the doses so the same 1 mSv/year limitation will apply.
NCRP 151 recommends
Controlled areas 0.1 mSv week–1 (5 mSv y–1)
Uncontrolled 0.02 mSv week–1 (1 mSv y–1)
There are also time average dose rates TADR and Instantaneous dose rates IDR
Below is the answer to another question that I gave a while ago, and you should find it helpful:
It is worth adding something to the second part of your question. As you know there are no safe radiation doses (in theory at least). So the objective of shielding is to to ensure that the doses outside the shielded area do not exceed legal limits, or other requirements that may be set nationally. This creates problems in many countries, which do not have their own regulations and tend to follow guidelines available internationally. The most important problem for Engilsh language guidance is that the reccomendations from the US are quite different to those from the EU and the UK. Also, the EC and UK (and many other countries) impose an additional limitation referred to as a Dose Constraint. This is a level used during, for example, the planning of a building to facilitate optimization. Briefly the design levels that tend to be quoted in the US literature are often as high as 50 mSv/y (occupational dose limit). The legal limit often used in EC countries is often as low as 1 mSv/y (public dose limit) and when designing a building this is often reduced further to the design dose constraint of 0.3 mSv/y. All of this is discussed in some detail in the document;
"The Design of Diagnostic Medical Facilities where Ionising Radiation is used."
available for download from my Researchgate page at:
https://www.researchgate.net/publication/235997041_The_Design_of_Diagnostic_Medical_Facilities_where_Ionising_Radiation_is_used
Book The Design of Diagnostic Medical Facilities where Ionising R...
Thank you all for your prompt and highly valued contributions to the question posed.I find them very useful. Meanwhile, i am a Radiographer with a very strong and developing passion for Radiation, Environmental Protection and Dosimetry. Being a beginner i am glad to glean from the wealth of experience of seasoned professionals like you.
My pleasuure Flavious. The publication referred to gives a framework which stands up very well. From time to time some new technical data becomes available but the approach is robust and is very useful. Glad to help.
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