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Over the last decade RTTs have become more and more involved in research. Some of this research is part of the service evaluation but more recently many RTTs are doing a master education or even a PhD track. Quite often RTTs have the opportunity to investigate alternative or improved setup strategies in radiotherapy, for example comparing different setup strategies or immobilisation equipment. We have seen this involvement result in an exciting increase in RTT-abstracts! On the downside, however, as evidenced by quite a few abstracts as well, a proper statistical analysis of the findings seems to be challenging. For instance, we often encounter analyses where the sign of the setup error has been discarded, or where the mean of the setup errors is compared rather than their SD.

This teaching lecture is refresher moment for RTTs and will give a complete and clear overview on how to handle data concerning geometric uncertainties based on straightforward examples from simulations and clinical practice. We will provide a description of the effect of random and systematic errors on the dose distribution. We will then explain the calculation of mean, systematic and random errors using practical examples in excel. Subsequently, we will explain what statistical methods to use to compare the geometrical uncertainties of two different strategies. To clarify the issues with common mistakes we will also demonstrate the impact of a few types of frequent analysis errors.

For those interested we will provide an example excel to be used at home.