A novel daily QA system for proton therapy.

We describe the design and use of a daily quality assurance (QA) system for proton therapy. The QA system is designed to check the overall readiness of proton therapy system consistently within certain reference tolerances by a home-made QA device (the QA device). The QA device is comprised of a commercially available QA device, rf-Daily QA 3, a home-made acrylic phantom, a set of acrylic compensators with various thicknesses, and a mechanical indexing jig. The indexing jig indexes the rf-Daily QA 3, as well as the acrylic phantom, onto the patient treatment couch. Embedded fiducial markers in the acrylic phantom are used to check X-ray image quality and positioning alignment accuracy of the imaging system. The rf-Daily QA 3 is used to check proton beam output, range and symmetry with one single beam delivery. We developed in-house software to calculate beam range and symmetry, based on various ion chambers' readings inside the rf-Daily QA 3. With a single setup and one beam irradiation, the QA system is employed to check couch movement, laser alignment, image registration, and reference proton beam characteristics. The simplicity and robustness of this QA system allows for a total QA time of less than 20 minutes per room. The system has been in use at three proton therapy centers since June 2009.