Section 4 Radiation Induced Cataracts Answers and
1. ANSWER: A
FEEDBACK: A multislice CT scan results in a dose to the lens of the eye of less
than 5cGy. Cerebral angiography can contribute an additional dose of 5cGy to
the lens of the eye. The minimum dose that will produce a cataract in a single
exposure is about 2Gy. The correct
option is A. 0%.
2. ANSWER: A-FALSE, B-FALSE, C-FALSE, D-TRUE
FEEDBACK: In the lens, dividing cells are confined to the equatorial region.
Progeny migrate to the posterior pole of the lens. Cells damaged by radiation
lead to opaque fibers that congregate in the posterior pole; option A is False. The minimum
acute dose to produce a cataract is about 2Gy. 1Gy over 5 years will certainly
not result in a cataract; option B is
False. Prescription eyeglasses today are almost always plastic and
absorb little radiation. Lead glass is required to significantly attenuate x
rays; option C is False. Vision-impairing
cataracts take time to develop and are preceded by less-important opacities; option D is True.
3. ANSWER: A-FALSE, B-TRUE, C-TRUE, D-TRUE
FEEDBACK: A stochastic effect is one in which the severity of the effect is
independent of the dose and for which there is no threshold. In the case of a
cataract, there is a practical threshold of 2Gy, and the severity of the
cataract increases with the dose; option
A is False. The minimum dose, in a single acute exposure, required to
result in a cataract is indeed 2Gy; option
B is True. Cataractogenesis by radiation shows a substantial dose-rate
and fractionation effect (i.e., a larger dose is required if it is
protracted); option C is True.
For a given dose, high-LET radiations, such as neutrons and heavy charged
particles, are much more effective at inducing cataracts; option D is True
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