Room: AAPM ePoster Library
Purpose: To investigate the feasibility of using automated machine performance check (MPC) for routine machine quality assurance (QA) of a Halcyon.
Method: MPC is an integrated QA module in Halcyon system and utilizes the ISOCAL phantom with imaging to check beam and mechanical parameters. We compared MPC with our monthly QA results for beam output change, isocenter size, virtual-to-isocenter shift, and couch readout accuracy. Monthly QA results of nine consecutive months were compared with MPC results performed on the same day of monthly QA. In monthly QA, the isocenter size test is a modified Winston-Lutz test by acquiring portal images at different gantry positions using a DoseLab cube. To check the virtual-to-isocenter shift, the cube was aligned to lasers and moved to isocenter. Megavoltage orthogonal images were acquired, and the shift was recorded using a 2D-2D match method. The mean and standard deviation of each test result were calculated and a paired t-test comparison was performed.
Results: Comparing MPC with monthly QA, the differences in isocenter size and beam output variation were 0.02mm (p=0.37) and 0.47% (p=0.041), respectively. The difference in virtual-to-isocenter shift was 0.41mm lateral (p<0.001), 0.93mm longitudinal (p<0.001), 0.72mm vertical (p=0.005) while the difference in couch position readout accuracy was 0.35mm lateral (p<0.001), 0.28mm longitudinal (p=0.056), and 0.22mm vertical (p=0.29).
Conclusion: MPC agreed with monthly QA for the tests in the isocenter size and couch readout accuracy but not for the tests in the beam output and virtual-to-isocenter shift. However, their differences were small compared to institutional tolerance limits, indicating the potential of using MPC as an alternative method for routine QA. Future work will compare more QA tests and monitor their differences for a longer period