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Wednesday, June 23, 2010

CT scans--why not?

The New England Journal of Medicine this week published two articles on imaging technology.  The first was about the safety of CT scans and the second was about the indiscriminate use of radiological imaging of all kinds. Imaging of the human body is big business and important in the progress of diagnosis, but once a machine or technique is invented, its use is mostly unregulated and largely up to our discretion, without supporting scientific evidence of usefulness.

CT scans do cause cancer. This is because ionizing radiation causes cancer and CT scans carry lots of that. Every year 10% of Americans get a CT scan, and many people have multiples. Each CT scan carries 100 to 500 times the radiation dose of a standard chest x-ray if done properly.  If an error is made, much more radiation can be delivered. Sometimes a patient might find out about such an error, but most often there would be no symptoms and no recognition.

CT scans also do save lives.  They detect problems that would require emergency surgery before they are life threatening. They detect conditions which would remain painful or disabling mysteries for years without imaging. The trick is using them appropriately.

CT scans of the abdomen and pelvis usually carry the greatest radiation dosage because there is so much tissue that has to be penetrated in order to get a good picture. In this New England Journal article (http://content.nejm.org/cgi/content/full/NEJMp1002530?query=TOC) the patient in question got 2 CT scans of the head in short succession, arguably for no good reason, and one of them carried an erroneously high dose of radiation, resulting in significant brain toxicity. It could have happened to anyone.

Also an issue for this patient was the fact that a special CT scan called a perfusion scan was done to see if she was having a stroke. I have not ordered these yet myself, and just recently heard about a patient for whom such a scan was suggested as a way to evaluate an odd and transient symptom.  These brain perfusion CTs carry a much higher radiation dose than a standard head CT, with the risk of radiation damage to brain and scalp and obvious increased risk of malignancy. Since most of us have, at one time or another, had disturbing neurological symptoms, wooziness, confusion, dizziness and the like, such a scan may gain significant popularity in the future, with results that will be irreversible to the patients who receive them for inadequate indications.

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