The 2003 BIR report into Geometric Uncertainties is an excellent resource for understanding the nature of margin expansions in radiotherapy. However, the use of daily online IGRT negates some previous errors and replaces them with different, albeit smaller, sources of uncertainty. The ubiquity of intensity modulated techniques, especially VMAT and other rotational methods of delivery, also pose problems to application of these recommendations. 

This talk will explore the reasoning behind the need for an update to the 2003 report before discussing each source of geometric uncertainty in turn: delineation error, fusion error, target deformation, rotational error, intra-fraction motion, surrogate error, matching error and technical delivery error. Each source will be characterised, and practical, pragmatic methods of determining its magnitude will be explored.

Educational aims:

- To understand that some sources of geometric uncertainty in daily online IGRT are different to non-IGRT techniques

- To understand nature and measurement techniques appropriate for each source of geometric uncertainty

Reference: 

British Institute of Radiology Geometric Uncertainties in Radiotherapy: Defining the Planning Target Volume. 2003

1 CPD credit.

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Duration:39 mins