Introducing operator characteristic curves to define appropriate frequency of quality control tests: A case study involving whole breast radiotherapy image guidance.

Background And Purpose: Sampling theory and operator characteristic curves are methods that can determine an optimal schedule for quality control tests. We apply this method to positional data for whole breast radiotherapy since several surveys report inconsistent image guidance practice for this technique.

Materials And Methods: Positional errors were defined, for 55 consecutive breast cancer patients, by comparing the central lung distance measured on portal images with that obtained from the corresponding digitally reconstructed radiograph.