KEY POINTS
- This narrative review evaluated positioning and image-guidance literature published between January 2005 and April 2026, without formal meta-analysis or quantitative risk-of-bias assessment.
- Positioning errors are often regional and non-rigid: lower-neck and shoulder displacement, mandibular variation, swallowing motion, mask deterioration, weight loss and tumour regression may persist after global image registration.
- Reported interfraction shoulder displacement ranged from 2 to 6 mm, while shoulder deformation exceeding 6 mm has been associated with altered volumetric modulated arc therapy dose distributions.
- Six-degree-of-freedom couches, cone-beam computed tomography, customized immobilization and surface guidance improve reproducibility but cannot correct deformation or evolving anatomy.
- The authors propose linking detected mismatch to one of several actions: couch correction, patient repositioning, re-immobilization, repeat simulation or adaptive replanning.
CLINICAL TAKEAWAY
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Daily image guidance should answer more than whether a numerical couch shift is acceptable. Persistent regional mismatch or deteriorating immobilization should trigger an explicit clinical response, although this review does not establish universal thresholds for repositioning or replanning.