On Thursday, January 31, 2008 during a treatment of a patient an event occurred with the licensee's Leksell Gamma Knife Stereotactic teletherapy treatment unit (Model 24001 Type C).
The patient treatment plan called for three exposure fractions. The first fraction was initiated at 10:25 a.m., without incident. After the normal termination time of treatment, the couch retracted fully and the patient's head was withdrawn from the unit. However, the shielding doors on the unit did not close. An Authorized Medical Physicist (AMP) then entered the treatment room, walked behind the unit, and closed the shielding doors manually. The licensee estimates that the AMP received an exposure of no more than 0.0083 mrem while closing the shielding doors. The patient was removed from the treatment room and a radiation survey was conducted to verify that the shielding doors had closed completely.
Elekta was contacted (12:30 p.m. 01/31/08) and a service representative arrived and completed an evaluation of the Gamma Knife and could find no faults in any aspect of the Gamma Knife system operation. A decision was made by the Authorized User to complete the last two exposure factions. The remaining shots were successfully completed.
The patient did not receive a radiation dose deviating from the written directive from the shielding doors not closing. The licensee was in constant contact with DHFS throughout this incident. This event will be followed up by DHFS on the next scheduled inspection (02/19/08).
Event Report ID No WI-08-01
License No.: 79-1281-01
Event Type: HFS 157.13(17)(b)2.a - 'Equipment is disabled or thus to function as designed'