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Limitations of 2D Verification
•
Measurement of set-up errors is subjective depending on the quality of
the reference compared with the portal image.
•
Without markers, only bony anatomy is available as a surrogate for the
tumour or target volume.
•
Awareness of tumour motion, changes in target volume, proximity of
surrounding OARs to the high-dose region, and the impact of patient
weight-loss is very limited.
•
Portal images are often restricted by treatment field orientation. The
alternative is the labour-intensive production of imaging-only fields.