Surface-guided Radiation Therapy in Clinical Practice: A Review with Perspectives on Implementation in Resource-constrained Settings.

Surface-guided radiation therapy (SGRT) has emerged as a nonionizing image guidance modality that uses optical surface reconstruction for patient positioning, intra-fraction motion monitoring, and respiratory motion management. Although clinical adoption has expanded in high-income settings over the past decade, the technology remains underutilized in low- and middle-income countries where the global cancer burden is concentrated. This review synthesizes current evidence on SGRT technology, commercial platforms, clinical applications, quality assurance (QA), and workflow considerations, with emphasis on practical implementation in resource-constrained settings. The established role of SGRT in breast deep inspiration breath-hold monitoring, its emerging applications in palliative and cranial treatments, integration within hybrid image-guidance workflows, and role in online adaptive radiotherapy are discussed. Commercial platforms including AlignRT, C-RAD Catalyst/Sentinel, IDENTIFY, and the hybrid surface-thermal-X-ray ExacTrac Dynamic system are compared. QA recommendations based on American Association of Physicists in Medicine TG-302 and European Society for Radiotherapy and Oncology-Advisory Committee on Radiation Oncology Practice guidelines are summarised. Under-discussed limitations, including region-of-interest selection variability, body habitus and skin pigmentation effects on surface detection (where evidence remains limited), and over-reliance on surface surrogates for deep-seated targets are critically evaluated. Emerging low-cost alternatives, particularly smartphone-based Light detection and ranging surface tracking, are discussed as a potential pathway toward more equitable surface guidance in radiation oncology.