Physics quality assurance

The physics quality assurance (QA) program for pencil beam scanning at the Proton Therapy Center in Houston is presented. This program consists of machine-specific and patient-specific measurements. The program follows national and international recommendations. Machine-specific QA assures the accuracy and constancy of nine different delivery components. Recommendations for daily, monthly, and annual measurements are presented. Patient-specific QA includes plan review by the physicist and verification of plan parameters and image transfer to the record-and-verify system, as well as comparison of the planned dose distribution of every treatment field with the measured dose distribution in a water-equivalent phantom. Finally, the QA programs at other institutions are briefly reviewed.