Use of routine quality assurance procedures to detect the loss of a linear accelerator primary scattering foil

The effects of the mechanical loss of a stainless steel primary scattering foil on a 12-MeV electron beam from a dedicated intraoperative electron accelerator are discussed. Routine quality assurance tests, including dose output constancy, energy constancy, and beam uniformity (flatness and symmetry), were used to determine the nature of the malfunction when it occurred. It is concluded that these quality assurance checks, if done with the frequencies recommended by the AAPM Task Group 40 Report [Med. Phys. 21, 581-619 (1994)] and repeated at the time of occurrence, are sufficient to detect loss of an electron scattering foil.