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Allergy & Clinical Immunology Unit
Monday, June 11, 2012
What is a CT scan and when are they necessary?
A CT scanner rotates to take X-ray images from different angles all around your body. A computer puts these images together to form detailed, two-dimensional pictures. CT provides clearer, more detailed pictures than traditional X-rays.
Do children receive lower doses of radiation than adults?
Yes, with CT scans we reduce the dose according to the size and weight of the child. Children often receive a fraction of the adult CT scan dose.
The amount of radiation exposure from x-rays, CT scans and other imaging studies is limited to the minimum that is necessary to answer the diagnostic question. At Massachusetts General Hospital for Children (MGHfC), we use computer decision support systems to help doctors decide whether to do a new scan or if a previous scan may be used. These policies are part of MGHfC’s extensive efforts in dose reduction. Learn more about what Mass General Imaging is doing to reduce radiation dose from medical imaging, at http://www.massgeneral.org/imaging/about/reducing_radiation_exposure.aspx.
What is the risk that my child will get cancer if he/she gets a CT scan?
It remains unknown if the amount of x-rays delivered from diagnostic CT studies can cause cancer. However, it is prudent to exercise caution with the use of CT as if there is a small risk. Continued study of this issue is needed and is ongoing. We adhere to the Alliance for Radiation Safety in Pediatric Imaging philosophy of being cautious, and perform imaging tests only when necessary and at the lowest possible radiation dose to answer the clinical question. By doing this we maximize the benefits of these exams and minimize any potential risk.
Does the risk vary based on my child’s age?
Children are inherently more sensitive to radiation simply because they have more dividing cells. Typically, children of a very young age (less than 10 years), such as infants, have a higher risk than older kids. The child’s size is also important as there are more parts of the body separating the x-ray beam and the organs, which weakens the beam reducing the dose reaching these organs. This effect is much smaller in children of very young age or smaller size because they are in general thinner.
Do you have any concerns about the study’s results or methods?
There are two main limitations of the Lancet study. The radiation dose associated with CT scans done during the study period are significantly higher than currently used radiation doses, which implies that CT scans now have much lower risk of cancer than projected by the study. The study also lacked a control group. In other words, the study did not assess cancer risk in children of same age who did not have CT scan. Without the control group, the study can not conclude that radiation dose from CT caused the excess cancer in children.
Are there alternative tests my child could have that are equal to a CT scan?
Imaging studies that do not expose children to ionizing radiation such as ultrasound can be used first for various indications in the abdomen, followed by CT only if the ultrasound is equivocal. Magnetic resonance imaging (MRI) is another test that can be considered in the evaluation of the brain and spine. However, parents should not refuse needed CT scans, especially for potentially life-threatening conditions like head and spine injuries, pneumonia complications and chest infections.
Debra A. Gervais, MD, the Division Chief of Abdominal Imaging and Intervention and Pediatric Imaging, and Mannudeep K. Kalra, MD, an assistant radiologist in the Divisions of Thoracic and Cardiac Imaging and a Senior Fellow at the MGH Webster Center for Advanced Research and Education in Radiation, contributed to this story.
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