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Table 2 Overview of categories of errors sources for the system and observation parameters for error classification

From: Investigation of a real-time EPID-based patient dose monitoring safety system using site-specific control limits

Error category Clinical error (Y/N)? Observation Parameters Error sources
Acquisition error N Number acquisition frames/average EPID pixel offset/RTT comments Errors during acquisition of EPID images (i.e. missing frames, incorrect EPID calibration)
Watchdog system error N Synchronisation results/Difference between integrated predicted VS measured EPID and integrated measured EPID VS measured EPID in different fractions Errors caused by incorrect synchronization between predicted and measured EPID image and inaccuracy of predicted EPID image calculation
Watchdog user error N RTT comments/Number acquisition frames/Predicted EPID plan information VS patient information Errors made by RTTs using Watchdog software (e.g. started Watchdog software after beam-on, selecting wrong predicted plan)
Transfer and machine error Y MLC position and trajectory [28]/Gantry angle/Collimator angle [13]/Treatment information on image header/Beam profile calculation Errors during data transfer from TPS to treatment equipment and due to malfunctioning of treatment machine (e.g. erroneous field sizes, number of monitor units or collimator angles entered into the treatment machine, wrong MLC leaf positions or trajectory)
Patient related delivery error Y Beam profile/Visual assessment of predicted and measured EPID images/Normalised dose comparison/RTTs comment Errors caused by set-up errors or intra- and inter-fractional organ motion and due to inaccuracies during the individualised treatment (e.g. occurrence of gas pockets in the rectum, patient weight loss, and erroneous density correction in TPS).