doselength

Doselength is a metric used in radiology to quantify the cumulative radiation exposure along the length of tissue that is irradiated during an imaging examination, especially in computed tomography (CT). In practice, doselength is expressed as the dose-length product (DLP), which combines the radiation dose per image with the length of the scanned region.

Units and calculation: DLP is measured in milligray-centimeters (mGy·cm). It is calculated as DLP = CTDIvol × scan length (in cm), where CTDIvol is the CT dose index representing the exposure per rotation adjusted for pitch and other factors.

Relation to patient dose: DLP provides a practical proxy for overall radiation burden but does not directly equal the effective dose received by the patient. To estimate effective dose, conversion factors (k) for the scanned body region are used: effective dose (mSv) ≈ DLP × k (mSv per mGy·cm).

Applications and limitations: DLP is widely used in dose tracking, protocol optimization, and regulatory reporting. Limitations include dependence on scanner technology, scanning protocol, patient size, and the assumption of uniform risk across the scanned region; it does not capture organ-specific dose variations.

See also: CT dose index, CTDIvol, dose-length product, dose area product, radiation dose management.