Purpose: Routine quality assurance of onboard imaging systems (OBI) for proton therapy is a standard practice performed monthly according to the recommendations given in the American Association of Medical Physics Task Group Report No. 224 (AAPM TG #224). Methods utilized to carry out such tests are nearly identical to those in standard photon radiotherapy (AAPM TG #142) for both planar-kV imaging and CBCT imaging, where all measurements taken in subsequent months are with respect to a pre-determined baseline measurement. This study examines the variability of obtained image quality parameters across four proBeam treatment rooms and varying imaging techniques. Furthermore, this study examines the effects of possible artifacts and routine imager recalibration specific to ProBeam systems.
Methods: ProBeam OBI monthly quality assurance statistics were extracted from myQA and placed into another spreadsheet for statistical analysis. Descriptive statistics were obtained for each imaging parameter, from which a distribution of imaging parameters were obtained. A two way ANOVA test was also performed to compare the distribution of imaging parameters across all four rooms to determine if room dependence existed with respect to image quality.
Results: Of the tests undertaken, image quality statistics across the four treatment rooms were shown to be fairly uniform per specific room, but varied slightly when compared to each other. This was expected due to variability across rooms as well as initial commissioning data.
Conclusion: OBI systems for proton therapy are fundamental to ensure proper patient setup and alignment for treatment, and routine quality assurance tests are fundamental for proper safety. Furthermore, the utilization of a succinct SOP ensures that imaging parameters obtained will be as uniform as possible, despite that parameters will most likely be different across rooms.