During patient alignment, the snap ring dropped from the standard treatment couch (stc).The couch top rolled to the hardware limit (17.8 degrees), which is beyond the acceptable limit of 5 degrees.The patient did not fall off the couch and no mistreatment occurred.There are no known injuries.
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The root cause was discovered during repair and is attributed to system wear.Since the linkage mechanism continued to support the patient until it completely disconnected, this change of position was sudden and significant.Until the point of disconnect, the linkage continued to function as intended.Any motion allowed by the linkage would be accounted for by the target locating subsystem and handled in the same manner as the patient making small motions.The mechanism failure occurred during the patient alignment phase and effectively rendered the system inoperable as the patient could no longer be aligned.Because of frequent patient tracking, there is no risk of mistreatment beyond what is normally accepted.The major risk of this event would be the patient falling from the table, but this did not occur.
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