[Multicenter Online Evaluation of IGRT Irradiation Position Accuracy Using an EPID-based End-to-end Postal Audit]

This study aimed to propose an online evaluation method for the overall assessment of irradiation positional accuracy across multiple institutions.

A postal phantom was used to perform end-to-end tests of irradiation positional accuracy on 18 radiotherapy systems equipped across 16 institutions. Electronic Portal Imaging Device (EPID) images acquired after the final position verification were automatically analyzed. The accuracy of the proposed method was validated by comparing it with commercial analysis software.

The mean absolute positional errors±standard deviations at a gantry angle of 0° were 0.18±0.16 mm in the X direction and 0.54±0.28 mm in the Y direction. At a gantry angle of 90°, the errors were 0.21±0.18 mm in the Z direction and 0.42±0.34 mm in the Y direction. Although CT and radiotherapy system configurations varied among institutions, all EPID images were successfully analyzed using the proposed method. In addition, the results were generally consistent with those obtained using commercial analysis software.

This method was shown to be applicable across multiple institutions with different system configurations and to enable comprehensive online evaluation of irradiation positional accuracy.