CT protocol optimisation for oncologic surveillance imaging: phantom-based comparison of multi-scan and single-scan acquisition strategies

Computed tomography (CT) plays an important role in oncologic surveillance after treatment of gynecological malignancies, including patients treated with vaginal electronic brachytherapy (eBT). This phantom study evaluated CT acquisition strategies for oncologic surveillance, focusing on radiation dose reduction and objective image quality in the cranial, thoracic, and upper abdominal regions assessed quantitatively. CT acquisition protocols were investigated using an anthropomorphic Kyoto Kagaku phantom. Two acquisition strategies were analysed: a multi-scan approach with separate acquisitions for the head, neck, thorax, and abdomen-pelvis, and a single-scan head-torso acquisition with region-specific reconstructions. Different exposure parameter settings and reconstruction kernels were evaluated. Objective image quality was assessed using semi-automated region-of-interest (ROI) measurements with a custom FIJI/ImageJ macro. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and Artifact Index (AI) were calculated for cranial, thoracic, and abdominal regions. For the single-scan protocols, CTDIvol decreased from 4.21 mGy in the standard protocol to 2.97-3.99 mGy in the optimized protocols, while DLP decreased from 410 mGy.cm to 287-388 mGy.cm. Across all anatomical regions, SNR and CNR remained comparable with the standard protocol. Thoracic CNR ranged from 2.68 to 3.01, abdominal CNR remained stable in both liver and aortic regions, and AI demonstrated only moderate variability across the optimized protocols. Optimized CT acquisition protocols reduced radiation dose while preserving the evaluated objective image quality metrics in the cranial, thoracic, and upper abdominal regions. Among the evaluated configurations, a reduced dose single scan head-torso acquisition using reduced tube voltage and tube current modulation showed a favourable balance between radiation dose reduction and objective image quality under the investigated phantom conditions and was identified as a candidate protocol for subsequent clinical and reader performance validation.