143 / 1542
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.