Development of CBCT-Guided Online Adaptive Radiotherapy

Background: Online adaptive radiotherapy (oART) can change the dose distribution briefly to match the shape of the targets and organs at risk. Cone-beam computed tomography (CBCT)-guided oART has been introduced in clinical practice and is expected to improve clinical outcomes. This technology allows treatment as an extension of conventional CT-based image-guided radiotherapy technology and has the advantage of relatively short treatment times. However, the clinical and dosimetric benefits of oART have not yet been adequately reported. Methods: We systematically reviewed previous studies evaluating CBCT-guided oART in patients with malignancies. Case reports, conference abstracts, letters, editorials, and reviews were excluded. PubMed was searched from January 2019 to 22 November 2025, supplemented by hand searching. Study design, cancer site, workflow, treatment time, dosimetric outcomes, feasibility, and clinical outcomes were extracted. Owing to clinical and methodological heterogeneity, findings were synthesized narratively. Results: A total of 127 studies were included. Across most studies, adapted plans improved target coverage and reduced or maintained doses to organs at risk compared with scheduled plans. This review provides an overview of the workflows and latest developments in CBCT-guided oART. Furthermore, the clinical and dosimetric benefits at each site, including the chest, abdomen, pelvis, head, and neck, are shown. Conclusions: The development of oART is expected to lead to the introduction of personalized medicine and improve the clinical outcomes of patients with various cancers. Further research and clinical trials are warranted to establish CBCT-guided oART. This review received no external funding and was registered in PROSPERO (CRD420251237632).