Assessment of Shielding Effectiveness for Radiation Dose Reduction in Adult Brain Photon-Counting Computed Tomography: A Polymethyl Methacrylate Phantom Study

Background: The efficacy of lead-equivalent shielding in modern photon-counting computed tomography (PCCT) for adult brain imaging remains under debate and therefore requires quantitative evaluation under controlled conditions. This study aimed to quantify the radiation dose reduction to out-of-field radiosensitive organs and the effective dose (E) achievable using supplementary lead shielding during adult brain PCCT, employing a polymethylmethacrylate (PMMA) anthropomorphic phantom.Materials and Methods: A PMMA phantom was scanned using a first-generation PCCT system with a standard adult brain protocol under two conditions: unshielded and shielded. Shielding consisted of a 0.5 mm lead-equivalent neck collar and apron, which were applied after scout acquisition. Organ equivalent doses were measured at 55 anatomical sites using thermoluminescent dosimeters. The E was calculated using tissue weighting factors from International Commission on Radiological Protection (ICRP) Publication 103 and was compared with doselength product (DLP)-based estimates.Results and Discussion: Lead shielding resulted in statistically significant dose reductions (all false discovery rate-adjusted <i>q</i><0.05) in multiple out-of-field organs, including the breast (83.3%), esophagus (88.5%), lungs (85.2%), and thyroid (44.5%). The overall E was reduced by 8.7%, from 2.98 mSv to 2.72 mSv. A substantial methodological discrepancy was observed, as DLP-based <i>E</i> estimates were 47%–52% lower than those derived from phantom measurements using ICRP Publication 103.Conclusion: This phantom study demonstrates that lead-equivalent shielding can significantly reduce radiation dose to out-of-field organs during adult brain PCCT. However, achieving this benefit is critically dependent on proper procedural implementation. Shielding must be applied after scout (localizer) acquisition to avoid interference with the scanner’s automatic exposure control system. The marked discrepancy between dose estimation methods indicates that DLPbased values, while useful for population-level benchmarking, have inherent limitations for precise, protocol-specific optimization. These findings support the targeted and protocol-appropriate use of shielding for vulnerable patients, in accordance with the As Low As Reasonably Achievable (ALARA) principle.