[90313474]
(b)(4), facility in (b)(6), reported the protura system began to unexpectedly move after a 6-degree correction was applied and patient treatment was started. This caused the linear accelerator to stop treatment and the patient was realigned to the correct position and treatment continued. Upon investigation, it was determined that the move of the protura was from an error message from a prior patient treatment (error mb-err-52, which was not cleared), and while this error message was present, the protura software buffered icom data. The icom data contains the pedestal location. Since the error message was active during 2 additional patient treatments, the pedestal movement continued to be buffered while positioning these interim patients, the pedestal motion was then processed by protura software once the error was cleared. The 'catch-up' processing is what lead to protura having a delayed recognition to the pedestal motion, which then lead to an unexpected activation of the protura auto load/unload feature. This problem occurred because the software thread handing the icom messages, which are specific to elekta linacs, stopped looping when the mb-err-52 error message was displayed. This message was displayed after the therapist had completed the patient set-up with protura robotic adjustments and prior to patient treatments. This message was then left up for 53 minutes while ongoing positions and states of the elekta linac were communicated from the icom system and buffered by the protura software. Once the error message was acknowledged, the protura started to process the buffered icom data with linac status. This buffering was still occurring when the therapist setup the next patient to use protura. Due to the buffering and position deviations, additional error messages were displayed in the protura software. The user was required to manually open a patient twice, and override the pedestal threshold warning prior to making a desired protura shift for patient alignment. After the user had positioned the patient and a minute and nine seconds had passed, the protura software processed the buffered pedestal location moving across automatic couch zero thresholds, and protura started a move to zero from the shifted position. This motion caused the protura software to provide an external inhibit to stop any treatment delivery. There have been no confirmed adverse effects of this incident.
Patient Sequence No: 1, Text Type: D, B5