Computed Tomography

The significant value of computed tomography (or CT) for detecting a myriad of conditions and diagnosing injuries is marred by the danger CT poses due to the radiation it emits. Although CT scans are essential for detecting certain life-threatening diseases and injuries, their overuse can place vulnerable patients at risk for cancer.

CT creates cross-sectional and three-dimensional images from X-rays taken from multiple angles. Due to the need for multiple X-ray emissions, the amount of radiation emitted by CT is significantly more than that emitted by conventional X-ray techniques.

The potential harm that these increased doses of radiation pose for the more susceptible patients, especially children, has led to calls for restricting the use of CT in all but the most essential cases. According to the National Cancer Institute of the National Institutes of Health, approximately 5 to 9 million CT scans are performed on children every year in the United States. Researchers have estimated that a third of these scans may be unnecessary. Safer tests, such as magnetic resonance imaging (MRI) and ultrasound, can provide the necessary diagnostic information in a significant portion of these cases. These tests do not use radiation and are also less expensive and more portable.

A study published in the June 2012 online edition of The Lancet found 75 cases of leukemia and 135 cases of brain cancer among 180,000 British children who received scans between 1985 and 2002. The authors of the study determined that the children’s risk for cancer increased as the number of scans they received increased. Those children who received two or three CT scans before the age of 15 had three times the risk for brain cancer than the general population. The researchers also found that 5 to 10 CT scans had three times the risk for leukemia. It should be noted, however, that the baseline risk (i.e., the risk without receiving CT scans) is extremely low; only 4.5 cases of leukemia and 3.5 cases of brain/central nervous system cancer for every 100,000 individuals. It should be noted that the above study was observational, and there was no unexposed control group. The reasons for the CT scans on the children were not given although those who were diagnosed with cancer shortly after the CT scan were excluded from the study.

The American College of Radiology (ACT) has stated that parents should not refuse to have their children undergo CT scans for potentially life-threatening conditions such as injuries to the head and spine and diseases such as a pneumonia and chest infections. However, the ACT has also stated that CT should not be used as the first diagnostic imaging procedure under other conditions such as appendicitis. In these cases, ultrasound is recommended as the first line diagnostic procedure, with CT scans only when the ultrasound is inconclusive.

Children are especially susceptible to the effects of radiation due to three specific characteristics:

• They are significantly more sensitive to radiation than adults.

• They live longer than adults, which provides a longer period of time for the expression of radiation-induced damage.

• They may receive higher doses of radiation than necessary due to CT settings that are not set properly for their smaller size.

As with all uses of radiation (X-rays, CT scans or airport body scanners), the risks must always be weighed against the benefits. When other methods can just as easily be used to make a reliable diagnosis, they should be employed regardless of the relatively low individual risk of CT scans. However, if the physician has no other method for properly evaluating the patient’s condition, CT should not be avoided. When children need to be subjected to CT, special care must be taken to adjust the levels and distribution of radiation to the lowest settings required for proper imaging.

International organizations in charge of assessing the risks of radiation have determined that there is no low-dose threshold for radiation-induced cancer, i.e., there is no amount of radiation that can be considered completely safe. It follows, therefore, that any exposure to radiation should be weighed against the advantages it provides. Often, the convenience of a procedure is used to justify its use despite the risk it poses to the patient’s health. When considering the unique susceptibility of children to the effects of radiation, CT scans should only be performed when no other diagnostic tool can provide the necessary vital information.

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Juliette Siegfried, MPH

Juliette Siegfried, MPH, has been involved in health communications since 1991. Shortly after obtaining her Master of Public Health degree, she began her career at the National Institutes of Health in Bethesda, Maryland. Juliette now lives in Europe, where she launched ServingMed(.)com, a small medical writing and editing business for health professionals all over the world.

Juliette's resume, facebook: juliette.siegfriedmph, linkedin: juliettes, (+31) 683 673 767

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