Abstract
This educational review provides a comprehensive overview of adaptive radiation therapy (ART), an advanced approach to adjusting radiotherapy plans in response to anatomical or physiological changes during treatment. It classifies ART into three methods, i.e. offline, online, and real-time, distinguished by the timing of plan modifications relative to the treatment session. The review emphasises the importance of monitoring discrepancies between planned and delivered doses through advanced imaging and dose-tracking techniques, and how timely adaptation can exploit this information to maintain target coverage and minimise unnecessary exposure of healthy tissues. Key enabling technologies are discussed, including high-quality on-board imaging modalities (CT, cone-beam CT, MRI, PET) for accurate visualisation of current anatomy, deformable image registration and automated contour propagation for efficient mapping of anatomical changes, and reliable dose recalculation on images from the treatment machine to ensure dosimetric accuracy of adapted plans. Equally important, rigorous quality assurance (QA) protocols are outlined, including validation of image registration accuracy (to verify deformable alignment), end-to-end testing of the entire adaptive workflow, patient-specific plan verification via independent dose checks or in vivo dosimetry, and thorough risk analysis (such as failure mode and effects analysis) to anticipate potential errors. Clear adaptation criteria and multidisciplinary team oversight are recommended to ensure that adaptive interventions fulfil the promise of improved tumour control and reduced toxicity without compromising patient safety.