How can I find your guidelines for CT radiation limits? I am 60 years old, both my parents with cancer (mom died), and the insurer recommended me to do a hip CT even though the orthopedic doctor clearly wrote MRI in the referral. I understand the insurer’s preference to save money but given my radiation concern, exacerbated by age and family history and the fact that I already had 5 XRay imaging sessions in the past 12 months (three dental and 2 chest views) – I of course prefer to go for the MRI option. I tried to find in your site any official reference (because they said that “according to the AAPM there is zero risk for me”) – but failed. Can you please advise – considering my history, age, and previous xray sessions this year – what would you consider as an exposure to avoid? Is there really a zero risk? Shouldn’t I insist on the MRI – as recommended by the doctor? Basically I see the discrepancy between the clinical doctor and the administrational doctor. And I need to know that they don’t just use your establishment name in order to “disarm” me and save some dollars… Your insights will be highly appreciated. Especially if you would have advised to insist on the MRI (all considered)

The AAPM's public education website and “Ask the Expert” section is intended to provide basic education about medical physics. The AAPM members who respond to questions are not medical doctors and cannot make medical decisions or recommendations about specific clinical situations. However, we can provide some general information about medical imaging physics, technology, and acceptable practice.

The decision about the most effective test to answer a clinical question is best made by the care provider who is most familiar with the patient's condition. Providers can utilize "clinical decision support" tools such as the American College of Radiology's Appropriateness Criteria (1), which produces evidence-based guidance on the proper imaging exam for a given condition. The decision about whether to have CT vs MRI is not just a matter of the lowest cost or the patient’s preference. The images produced by CT and MRI provide different information, and one test or the other may be more appropriate depending on the clinical question that needs to be answered.

Many experts believe that a patient's previous radiation exposure history should not be considered when a decision is made about a diagnostic test in the future (2). There is no evidence that the effects of radiation are cumulative, so each new exposure is independent of the previous ones. Consequently, there is no lifetime radiation dose upper limit for medical exposures (2). Patients should not be denied appropriate medical care (such as x-rays or CT scans) just because they received medical radiation in their past.

Regarding the risks associated with diagnostic imaging, the risk of harm from any diagnostic imaging exam is statistically insignificant (3). There is an association between the radiation dose received and the risk of future cancer at high doses such as those from atom bombs (eg, Hiroshima and Nagasaki) and nuclear power accidents (eg, Chernobyl), but no such association has been proven at the much lower doses associated with medical imaging. It should be noted that MRI does not use ionizing radiation.

To summarize, there is no CT radiation dose limit, the best exam for you may be an MRI or it may be a CT (or something else), and your medical team is advised to utilize evidence-based guidelines to help decide which test is best for you. Your prior radiation exposure from exams like dental x-rays, chest radiographs or even CT or nuclear scans should not influence whether you can receive additional imaging. To do so would deprive you of the benefits of that imaging. Imaging facilities that follow best practices ensure that CT radiation levels are kept to the necessary minimum to provide adequate image quality for making an accurate diagnosis.


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