Artificial intelligence for radiation dose reduction in computed tomography: a narrative synthesis of clinical evidence from 2020 to 2025

Computed tomography (CT) is essential to modern clinical practice but contributes substantially to population radiation exposure, particularly in oncology, paediatric and screening pathways. In line with the as low as reasonably practicable principle and IR(ME)R requirements, there is growing interest in the use of artificial intelligence (AI) to reduce dose without compromising diagnostic performance. This work synthesised evidence published between January 2020 and May 2025 on AI-based strategies for CT dose optimisation, including deep learning reconstruction, denoising and workflow automation. A systematic search of PubMed, Scopus and IEEE Xplore identified 1,224 records. After removal of 239 duplicates and screening of abstracts and full texts, 86 studies met the inclusion criteria. Eligible studies reported clinical or patient-based outcomes relating to radiation dose, diagnostic accuracy, image quality or feasibility. Phantom-only work, non-CT imaging and conference abstracts without full text were excluded. Due to methodological heterogeneity, findings were synthesised narratively and grouped by anatomical region and AI application. Across indications, AI consistently enabled substantial dose reductions while maintaining diagnostic adequacy. Chest imaging demonstrated 30%-95% reductions, with ultra-low-dose protocols (∼0.1-0.5 mSv) supporting lung cancer screening and nodule detection. Abdominal and hepatic imaging achieved around 40%-70% dose reduction with preserved lesion visibility. 'Double-low' and 'triple-low' vascular protocols reduced both radiation and iodine by 40%-75%. Paediatric applications reported 50%-95% reductions, in some cases approaching doses comparable to radiography. Workflow AI, including auto-positioning and scan-length optimisation, provided additional independent benefits. However, most studies were single-centre and vendor-supported, and sensitivity for very small or subsolid lesions declined at the lowest doses. Altered image texture at high denoising strengths and limited multicentre validation remain concerns. Overall, AI offers clinically meaningful radiation dose reductions of roughly 40%-90% across multiple CT applications while preserving diagnostic confidence. The strongest evidence relates to chest screening, oncology follow-up, vascular imaging and paediatrics. Successful NHS implementation will require governance, quality assurance, training and multicentre evaluation.