Advanced Monte Carlo Modeling of Automatic Exposure Control Vulnerabilities: Patient Positioning and Metallic...

This study investigates the influence of arm positioning and metallic objects on radiation dose distribution during emergency CT scans, where time-critical workflows demand both speed and precision. Sub-optimal arm positioning and metallic artifacts can significantly alter dose patterns and compromise patient safety. Five clinical cases undergoing chest, abdomen, and pelvis (CAP) CT scans with automatic exposure control (AEC) at 120 kVp were analyzed using GATE/Geant4 Monte Carlo simulations. Patient-specific voxel models were generated from clinical CT datasets, and the scanner was modeled with z-axis tube current modulation. Variations in arm position (arms raised, crossed, or positioned alongside the torso) and the presence of metallic objects such as belts, keys, and necklaces were simulated. Dose maps were extracted in voxel format, and patient-specific CTDIvol-like metrics were computed and compared with scanner-reported CTDIvol values. Significant dose alterations were observed due to non-optimal arm positioning and metallic artifacts. Cases 1 and 4, both with metallic belts, exhibited elevated pelvic doses of 3.448 × 10⁻³ mGy and 3.658 × 10⁻³ mGy. Case 2, with arms crossed over the chest, recorded a 52% higher chest dose (5.244 × 10⁻³ mGy) compared to Case 1. Case 5, with arms positioned downward and a necklace, registered the highest maximum dose (5.475 × 10⁻³ mGy), 105% higher than the lowest dose in Case 3, where arms were raised with minimal metallic interference. Comparison with scanner-reported CTDIvol showed agreement within - 1.6 to - 17.8% across cases, confirming model consistency despite the absence of angular modulation. Improper arm positioning and metallic artifacts increase radiation dose in emergency CT, particularly in sensitive regions. Optimized positioning and artifact management are essential, even under time constraints, to ensure safe and effective dose delivery. Emergency radiology protocols should emphasize rapid but accurate arm positioning and removal of metallic objects to minimize radiation risks without compromising diagnostic quality.