Metal artifact reduction in spectral computed tomography for intracavity brachytherapy in cervical cancer patients: a prospective study

This study aims to evaluate the effectiveness of combining virtual monochromatic images (VMI) with metal artifact reduction (MAR) algorithms in reducing metal artifacts in cervical cancer patients undergoing intracavitary brachytherapy. Fifty cervical cancer patients scheduled for intracavitary brachytherapy underwent spectral computed tomography (CT) images. VMI + MAR/no-MAR were reconstructed at energies ranging from 40 to 140 keV. CT attenuation and image noise (standard deviation) were measured to calculate the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) for the most prominent artifacts, and the artifact index (AI) for the cervix, bladder, and rectum. Objective metrics were compared between the VMI + MAR and VMI + no-MAR groups. Subjective image quality was evaluated using a 5-point Likert scale, focusing on artifact reduction, soft tissue contrast, and contouring preference. Geometric distortion was assessed by measuring the long axis, short axis, and long-to-short axis ratio (L/S) of the titanium applicator. Contouring consistency was quantified using the Dice Similarity Coefficient (DSC) and 95th percentile Hausdorff Distance (HD95) between two radiation oncologists. VMI + MAR significantly reduced the AI for the cervix (relative 34.74%-88.51% reduction) and rectum (relative 11.31%-81.35% reduction) compared to VMI + no-MAR across all energies (all p < 0.05). SNR increased from 0.70–1.00 to 1.75–1.97, and CNR improved significantly from 90 keV onwards (p < 0.05). 140 keV + MAR achieved the highest SNR and CNR with the lowest AI. Subjective assessment further confirmed that 140 keV + MAR offered the best balance between artifact reduction and soft tissue contrast, with significantly higher scores for artifact reduction and contouring preference (p < 0.001). Distortion analysis showed that with increasing VMI energy, long (40-140 keV: from 8.10 to 6.17 mm) and short axes (40-140 keV: from 6.93 to 5.55 mm) decreased, and L/S approached 1 (p < 0.001). Contouring consistency analysis further demonstrated that 140 keV + MAR achieved the highest DSC and lowest HD95 among all energy-MAR combinations, indicating superior reproducibility of target and organ-at-risk delineations. For the investigated cases and imaging procedures, high-energy VMI combined with MAR, particularly 140 keV + MAR, provided the most effective balance of artifact reduction, geometric accuracy, and clinical contouring suitability.