Pushing the limits of CT localiser dose reduction. How low can we go?

Abstract

Purpose: Optimising radiation dose in CT begins before image acquisition, with the often-overlooked localiser scan. Localisers are performed for CT examinations, resulting in a small but important contribution to cumulative patient radiation dose, while also influencing scan range selection and automated exposure parameters. This study evaluates the use of tin (Sn) filtration to reduce radiation dose in CT scan localisers of the brain; kidney, ureter and bladder (KUB); and low-dose thoracic CT. Tin filtration functions as spectral beam shaping by selectively removing low-energy photons from the X-ray spectrum. These low-energy photons contribute disproportionately to patient dose while offering limited benefit to image formation due to their higher likelihood of being absorbed superficially rather than reaching the detector. By hardening the beam and increasing its mean photon energy, Sn filtration improves dose efficiency and reduces unnecessary radiation exposure without compromising the anatomical information required for scan planning. Given that localiser images are primarily used for positioning and protocol planning rather than diagnostic interpretation, the application of Sn filtration represents a rational optimisation strategy aligned with radiation protection principles such as ALARA.