Room: Exhibit Hall
Purpose: To develop and validate an efficient machine performance and quality assurance (QA) protocol using the integral quality monitor (IQM) system, as well as to demonstrate the operation of the IQM system and QA protocol by characterizing the performance of several linear accelerators across multiple institutions.
Methods: The IQM system mounts to the treatment head of a linear accelerator and consists of a large area ionization chamber with a gradient in the electrode plate separation along the direction of MLC motion. A series of MLC defined apertures were created as multi-segment QA fields to evaluate the dosimetric constancy of a linear accelerator as a function of gantry and collimator angle and aperture position. The QA protocol was designed to satisfy TG-142 measurement recommendations for photon beam output, energy, symmetry, and flatness as well as jaw position and dynamic-leaf motion.
Results: A 12-segment and 8-segment QA field was measured using the IQM system. The relative standard deviation of the measured counts per segment was < 0.5% per institution and < 3% across all institutions based on multiple measurements and different measurement days. The 8-segment QA field was measured at three different institutions with good agreement of measured counts per segment.
Conclusion: The proposed QA protocol in combination with the IQM system provides an efficient dosimetric characterization of a linear accelerator and validates the constancy of beam output as a function of gantry and collimator angle and MLC-defined aperture position. The multi-segment QA fields meet the measurement standards as defined by TG-142 and were tested successfully using two different linear accelerator manufacturers across three institutions. The IQM system provides a very efficient process for performing quality control and quality assurance of a linear accelerator, and allows for future automation of these tests.