The potential role of online adaptive radiotherapy in soft tissue sarcomas

Soft tissue sarcomas (STS) are a heterogeneous group of mesenchymal malignancies that typically require multidisciplinary management, including surgery, radiotherapy (RT), and systemic therapy. Conventional RT relies on a static plan created at simulation and does not directly account for inter-fraction anatomical changes. Online adaptive radiotherapy (ART) is a treatment paradigm in which imaging acquired immediately before each fraction is used to re-evaluate target volumes and organs at risk and to re-optimize the dose distribution before delivery. This narrative review summarises the current evidence on online ART in STS, with explicit attention to the level of evidence supporting each claim. We describe the technical platforms (cone-beam CT–guided and magnetic resonance–guided systems, including 0.35 and 1.5 T MR-Linac), the adapt-to-position (ATP) and adapt-to-shape (ATS) workflows, dosimetric studies, retrospective clinical series, professional society guidance, and ongoing prospective trials. Most current evidence in STS is dosimetric, planning-based, or single-institution retrospective; clinical benefit over modern image-guided IMRT/VMAT remains to be demonstrated in prospective comparative studies. We also outline practical recommendations for patient selection, workflow design, quality assurance, and research priorities, including a structured tabular synthesis of representative studies. Three structured tables are provided: representative studies of adaptive radiotherapy in STS, practical recommendations by clinical scenario, and prioritised research questions.