Adaptive radiotherapy (ART) is a next-generation approach that adjusts treatment plans based on anatomical changes during cancer treatment, improving precision and reducing side effects. Traditional radiotherapy relied on initial scans with margins to account for anatomical changes, but ART uses advanced imaging (CT, MRI, PET) and AI to dynamically adapt plans. ART can be conducted online (during treatment) or offline (between sessions). Advances in imaging and AI have made ART more feasible, enabling personalized treatment that better matches the patient's anatomy. ART optimizes the therapeutic ratio by adapting to changes in tumor and organ positions, ensuring accurate dose delivery while minimizing harm to healthy tissues. The review discusses the evolution of radiotherapy, the importance of ART in addressing anatomical variations, and the three major imaging modalities (MRI, CBCT, PET) used in online ART. It highlights the clinical applications of ART in various cancers, including cervical, lung, prostate, and head and neck cancers, and emphasizes the role of AI in enhancing treatment planning and quality assurance. ART offers improved outcomes by adapting to daily anatomical changes, reducing toxicity, and ensuring precise dose delivery. Current technical and clinical progress in ART is discussed, emphasizing the potential of integrating AI and advanced imaging technologies to further enhance the effectiveness and applicability of adaptive radiotherapy.Adaptive radiotherapy (ART) is a next-generation approach that adjusts treatment plans based on anatomical changes during cancer treatment, improving precision and reducing side effects. Traditional radiotherapy relied on initial scans with margins to account for anatomical changes, but ART uses advanced imaging (CT, MRI, PET) and AI to dynamically adapt plans. ART can be conducted online (during treatment) or offline (between sessions). Advances in imaging and AI have made ART more feasible, enabling personalized treatment that better matches the patient's anatomy. ART optimizes the therapeutic ratio by adapting to changes in tumor and organ positions, ensuring accurate dose delivery while minimizing harm to healthy tissues. The review discusses the evolution of radiotherapy, the importance of ART in addressing anatomical variations, and the three major imaging modalities (MRI, CBCT, PET) used in online ART. It highlights the clinical applications of ART in various cancers, including cervical, lung, prostate, and head and neck cancers, and emphasizes the role of AI in enhancing treatment planning and quality assurance. ART offers improved outcomes by adapting to daily anatomical changes, reducing toxicity, and ensuring precise dose delivery. Current technical and clinical progress in ART is discussed, emphasizing the potential of integrating AI and advanced imaging technologies to further enhance the effectiveness and applicability of adaptive radiotherapy.