Purpose: To adapt a single-setup in-house linac QA automation method to outside institutions.
Methods: Annual output quality assurance was automated in previous work for our Varian TrueBeam through the SAGE tool, TrueBeam Developer Mode, and the PTW UNIDOSwebline electrometer with in-house software. We adapted this work to 2 outside institutions based on their 2020 annual output QA procedures. Crucially, we hypothesized that outside institutions would see a strong hysteresis effect depending on the length of the beam off time between irradiations. Extensive scripts were created to address the tradeoff between short scripts and hysteresis across a hypothesized 140 measurements over 30 minutes.
Results: The expansion of our automation method to an outside institution highlighted the implicit clinic-specific assumptions that were made in the original Developer Mode scripts. Adaptation required adjustment of each beam to the energies, test parameters, and measurement repetition used in each clinic. Also, our in-house analysis program needed to be adjusted to accept the output file format from a Standard Imaging SuperMAX electrometer. Furthermore, the MLC model needed to be switched from HD to standard. It is essential that clinics using our technique are able to create their own scripts in a user-friendly manner. Our early emphasis on minimizing the time between irradiations while optimizing the inherent tradeoff with hysteresis was misplaced. The contributing clinics required only 53% of the measurements of our own clinic. Minimizing the duration of beam-off pauses yielded a small gain for the outside institutions. A 5-second beam off time after each irradiation was measured to be sufficient to reduce hysteresis to within 0.5% over 100 irradiations.
Conclusion: Widespread adaptation of the work will help to determine the appropriateness of digital electrometers and their analysis software for automation. Generalization is necessary to enable customization of this work to any cancer center.