Dose length product

Last revised by Andrew Murphy on 23 Mar 2023

Dose length product (DLP) measured in mGy*cm is a measure of CT tube radiation output/exposure. It is related to volume CT dose index (CTDIvol), but CTDIvol represents the dose through a slice of an appropriate phantom. DLP accounts for the length of radiation output along the z-axis (the long axis of the patient).

DLP = (CTDIvol ) * (length of scan, cm)

[units: mGy*cm]

DLP does not take the size of the patient into account and is not a measure of absorbed dose. If the AP and lateral dimensions of the patient are available, then the size specific dose estimate (SSDE) can be used to estimate the absorbed dose.

It is important to remember that the dose length product is not the patient's effective dose. The effective dose depends on other factors including patient size and the region of the body being scanned. Some multipliers, called k-factors, have been estimated to convert DLPs into effective doses, depending on the body region. If interested, consult reference 3.

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