Answer to Question #10781 Submitted to "Ask the Experts"
Category: Radiation Basics
The following question was answered by an expert in the appropriate field:
Why are the equivalent dose limits for skin and eye not included in 20 mSv effective dose limit?
The equivalent annual skin dose limit of 500 mSv that applies to occupational workers is based on the prevention of deterministic effects to the skin—i.e., noncancerous detrimental changes to the skin. Similarly, the limit of 150 mSv to the lens of the eye is based on deterministic effects, namely cataract production in the lens.
The International Commission on Radiological Protection (ICRP) has, however, assigned a tissue weighting factor of 0.01 to the skin, based on possible cancer induction, and equivalent dose to the skin may be weighted by this factor in determining effective dose. Consideration of the contribution of skin dose to effective dose becomes particularly relevant when a significant dose component is associated with low penetrating radiation that delivers dose primarily to the skin. It is clear that limitation of the effective dose to the recommended 20 mSv in a year is sufficient to provide protection against deterministic effects to the skin.
The ICRP has not assigned any tissue weighting factor for stochastic effects to the lens of the eye, and dose to the eye does not contribute to effective dose. The 15 mSv limit has been considered adequate for protection against deterministic effects, although there is some consideration being paid at present to reducing this limit in light of more information regarding visual impairment.
George Chabot, PhD