Quantifying Patient Positioning Errors and Radiation Dose Variation in Cardiac Computed Tomography Angiography

Accurate patient centring at the computed tomography (CT) scanner isocentre is essential for optimising radiation dose. This study aimed to quantify positioning errors, assess their relationship with radiation dose, and estimate the potential dose reduction achievable with optimal centring.

This retrospective observational study included adult patients (≥18 years) who underwent electrocardiography (ECG)-gated cardiac CT angiography between January 2023 and July 2025 at a tertiary hospital. Scans were performed using Siemens SOMATOM Force dual-source CT systems. Vertical and lateral deviations from the scanner isocentre were calculated from scout images using integrated analytics within the institutional dose monitoring platform (Qaelum NV, Leuven, Belgium). Radiation dose indices, including the volume-weighted CT dose index (CTDI_vol) and dose length product (DLP), were extracted from DICOM dose reports. Statistical analyses comprised descriptive statistics, correlation analysis, multivariable regression, and simulation of potential dose reductions with ideal centring.

Data from 399 patients were evaluated. Significant off-centring (>10 mm) occurred in 83% of scans in the anteroposterior (AP) direction and 50% laterally. Severe AP off-centring (>30 mm) was present in 39% of cases. Off-centring showed no independent association with CTDI_vol or DLP after adjustment for body mass index (BMI), age, and sex. Male patients demonstrated significantly greater off-centring in both the AP (p = 0.048) and lateral (p = 0.037) directions, and BMI category was significantly associated with off-centring magnitude in the AP (p = 0.031) and lateral (p = 0.022) directions. Literature-based scenario modelling suggested that ideal centring could hypothetically reduce mean CTDI_vol by approximately 12%, with a similar reduction in DLP.

Patient off-centring was highly prevalent in cardiac CT examinations. No independent association between off-centring and radiation dose was observed when adjusting for BMI, age, and sex. Literature-based scenario modelling suggests that meaningful radiation dose reductions may be achievable with optimum centring, although this requires prospective confirmation.