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Answer to Question #6057 Submitted to "Ask the Experts"Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT The following question was answered by an expert in the appropriate field: Q
My question is in regard to cumulative exposure. Is radiation exposure cumulative, meaning that if I have been exposed to more radiation over time than my wife, am I at a higher risk for cancer, or is risk more associated with a high acute exposure? The main motivation for my question is that I have had an abdominal CT and a head CT over the last year and I wonder if waiting some amount of time before I have any other x rays or CTs would be beneficial. Does the body recover in some way over time after the exposure?
A
This is a complicated issue and question. First, the incidence of being diagnosed and dying from cancer is statistical in nature. That is, it is impossible to predict if any one individual in the population will get cancer. Also, there is normal incidence rate in the population. In a population of 10,000 people, 2,500 will die of cancer in their lifetime. If every one of the 10,000 received 1 rem of radiation exposure, the increased cancer death rate would increase by 0.05 percent, so that the total cancer deaths would be 2,505. Of course, you cannot determine whom the additional five individuals dying will be. Even if you receive 10 CT scans and your wife none, your wife could develop cancer and not you.
Second, there is a phenomenon known as the dose dose-rate effectiveness factor or DDREF. From biology studies it is clear that if doses are fractionated or delivered over a long period of time, the higher cumulative exposures can be delivered due to repair of radiation effects. This is also the basis of using fractionated doses for patients undergoing radiation therapy for breast and other cancers. Consequently, a DDREF can be used when assessing cumulative radiation risk factors. Our estimates of radiation risk are based on acute doses. If one applies a DDREF of 2-3, the total accumulative exposure that might result in a cancer would be increased by a factor of 2 to 3.
Third, there have been no demonstrated affects of radiation exposures below 10 rem or 10,000 mrem. Diagnostic exposures seldom deliver acute doses of this magnitude. As noted in a Health Physics Society Fact Sheet, an abdominal CT scan delivers an effective dose of approximately 1,000 mrem and a head CT scan is about 200 mrem. Personally, I would not delay any diagnostic x-ray medical exam due to radiation exposures. The benefits outweigh the risks as noted in an Ask the Experts information sheet.
Answer posted on 9 March 2007. 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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