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Answer to Question #3058 Submitted to "Ask the Experts"Category: Radiation Effects — Genetic Effects The following question was answered by an expert in the appropriate field: Q
My question is concerned with the effects of the radiation given to the eyes and brain of a young child during multiple CT scans of the head. Sometimes the technician has to do more than one scan to get pictures without motion (in spite of attempts to hold the child still). What is the dose given during one scan and at what level of dose is the child at risk for cataracts or brain injury? Also, are cataracts that are induced by radiation corrected in the same manner as naturally occurring cataracts?
A
The radiation dose from a head CT scan to organs and tissues within the primary x-ray beam usually ranges from about 30 to 50 mGy, depending on the equipment and specifics of the examination. Radiation-induced cataracts fall in the class of deterministic effects. For these effects, severity is proportional to dose. There is a threshold dose below which severity vanishes. The threshold for cataract from acute radiation is now estimated at about 500 mGy of x-ray exposure. Radiation-induced cataracts behave generally similar, but not identical, to spontaneous cataracts. Effects on the brain are in two classes: deterministic and stochastic. Threshold doses for deterministic effects on the brain are quite large, generally thousands of mGy. Stochastic effects are those in which probability of effect is a function of dose. These effects include cancer, which may occur at relatively small doses. However, at the CT doses described above, the probability of cancer is so small as to be undetectable in patient populations. Conclusion: The risk of cataract from head CT is zero or nearly so. Data for brain cancer risk are inconclusive. The risk may be zero, but some studies suggest a very small risk. In any event, for medically justified CT exams, the potential benefit to the patient far outweighs any potential risk. S. Julian Gibbs, DDS, PhD
Answer posted on 10 October 2003. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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