Health Physics Questions and Answers - Question 172
(a) If the annual limit to the head is five rem deep dose equivalent, what is the purpose of the 15 rem eye dose equivalent?
(b) How can a person receive 15 rem eye dose equivalent without exceeding the annual TEDE limit?
(a) The purpose of the 15 rem non-stochastic limit to the lens of the eye is to prevent lens opacities (cataracts). The dose limit to the head a stochastic limit) and the dose limit to the eye (non-stochastic limit) are measured at different depths in tissue, 1 cm tissue equivalent depth for deep dose and 0.3 cm for eye dose; and for low penetrating radiation (such as beta or low-energy x-rays), doses at different tissue depths can be significantly different.
(b) The 15 rem eye dose equivalent applies to the exposure to the lens of the eye and is measured at a tissue depth of 0.3 cm. The 5 rem TEDE limit is the sum of the deep dose equivalent at a tissue depth of 1 cm and the committed effective dose equivalent. In general, a person can receive 15 rem to the eye (measured at 0.3 cm) without exceeding the 5 rem limit on deep dose equivalent when the head is exposed to beta or low-energy photon radiation, although it would be rare. for an individual to receive 15 rem eye dose equivalent without exceeding a deep dose equivalent of 5 rem.
(Reference: 10 CFR 20.1201)