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    • Section 4 Radiation Induced Cataracts Answers and Feedback

    • Section 4 Radiation Induced Cataracts Answers and Feedback 

      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%.

      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. 

      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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