Radiotherapy, a crucial cancer treatment, has evolved significantly over the years. Traditionally, treatment plans were based on initial scans and used additional margins to account for anatomical changes. However, advancements in delivery and targeting accuracy have led to a shift towards reducing these margins to decrease toxicity. Image guidance has revealed unaccounted anatomical changes, such as organ deformation, weight loss, and tumor shrinkage, necessitating the development of adaptive radiotherapy (ART). ART adjusts treatment plans according to these changes, either online (during treatment sessions) or offline (between sessions). Advances in medical imaging (CT, MRI, PET) and artificial intelligence (AI) have made ART more feasible and efficient. ART offers more precise cancer treatment by adapting to changes in the patient's body, leading to better outcomes with fewer side effects. The review introduces ART, a notable innovation that addresses anatomy changes and optimizes the therapeutic ratio. It discusses the significance of ART in accommodating patient anatomical changes during treatment and highlights the role of AI in enhancing ART effectiveness. The review covers different types of ART, including offline and online methods, their respective workflows, technologies, and clinical applications. It also presents a comprehensive guide on ART for healthcare professionals and trainees in radiation oncology. The evolution of radiotherapy and the need for ART are discussed, emphasizing the challenges posed by anatomical changes. The frequency, general workflow, and differences between offline and online ART are outlined. The implementation of AI in ART is highlighted, including its role in automating processes and improving precision. Three major imaging modalities for online ART—MRI, cone-beam CT (CBCT), and PET—are described. Each modality's advantages, limitations, and clinical applications are detailed. The effectiveness of ART is demonstrated through dosimetric and clinical results, particularly in treating cervical and lung cancers. Early clinical outcomes show significant improvements in dose distribution and reduced toxicity, supporting the potential of ART in enhancing cancer treatment.Radiotherapy, a crucial cancer treatment, has evolved significantly over the years. Traditionally, treatment plans were based on initial scans and used additional margins to account for anatomical changes. However, advancements in delivery and targeting accuracy have led to a shift towards reducing these margins to decrease toxicity. Image guidance has revealed unaccounted anatomical changes, such as organ deformation, weight loss, and tumor shrinkage, necessitating the development of adaptive radiotherapy (ART). ART adjusts treatment plans according to these changes, either online (during treatment sessions) or offline (between sessions). Advances in medical imaging (CT, MRI, PET) and artificial intelligence (AI) have made ART more feasible and efficient. ART offers more precise cancer treatment by adapting to changes in the patient's body, leading to better outcomes with fewer side effects. The review introduces ART, a notable innovation that addresses anatomy changes and optimizes the therapeutic ratio. It discusses the significance of ART in accommodating patient anatomical changes during treatment and highlights the role of AI in enhancing ART effectiveness. The review covers different types of ART, including offline and online methods, their respective workflows, technologies, and clinical applications. It also presents a comprehensive guide on ART for healthcare professionals and trainees in radiation oncology. The evolution of radiotherapy and the need for ART are discussed, emphasizing the challenges posed by anatomical changes. The frequency, general workflow, and differences between offline and online ART are outlined. The implementation of AI in ART is highlighted, including its role in automating processes and improving precision. Three major imaging modalities for online ART—MRI, cone-beam CT (CBCT), and PET—are described. Each modality's advantages, limitations, and clinical applications are detailed. The effectiveness of ART is demonstrated through dosimetric and clinical results, particularly in treating cervical and lung cancers. Early clinical outcomes show significant improvements in dose distribution and reduced toxicity, supporting the potential of ART in enhancing cancer treatment.