I recently had a CT scan of the head in an emergency room. My medical record shows the radiation dose as DLP 582 mGY-cm. Can you tell me what this equals in terms of millisieverts?

DLP stands for Dose x Length Product and is one of the measures used to quantify radiation used during CT scanning. It is measured in units of mGy*cm. You asked about the dose expressed in milliSieverts, so you are interested in knowing the effective dose resulting from this CT scan. Effective dose is the sum of the individual organ doses for all organs that were irradiated, adjusted to account for the sensitivity of each organ to radiation. Because our knowledge of these sensitivities is for the average member of a population, not for any individual, effective dose applies only to populations and not to individuals. Therefore, we can say that a DLP of 582 mGy*cm from a head CT scan corresponds to an effective dose of about 1.2 mSv to the average adult. It may be helpful to compare this value to the average annual "natural background" dose in the US of 3.2 mSv from naturally occurring sources of ionizing radiation such as radon and cosmic rays. Effective doses in this range have not been associated with any negative health consequences, while the diagnostic information from a CT scan can have tremendous health benefits.

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