ABSTRACT
Quality assurance (QA) comprises all measures that ensure that a system functions as it did during acceptance and commissioning. Proton QA categories—machine and patient specifics—are the same as those of conventional radiotherapy but differ in execution as a consequence of the physics of protons and the delivery systems in particular. The clinically important dosimetric parameters as well as their measurement techniques depend on the delivery mode. Most institutions started operations with an extensive and time-consuming QA program, until sufficient data was gathered to show most common paths for failure. Most reference dosimetry is done in water. An essential piece of equipment is therefore a water tank allowing scans in three dimensions. Plane-parallel ionization chambers should be used for depth-dose scans, with the center of the inner surface of the window as point of measurement. A practical issue is the thickness of the front wall of a water tank.
