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The following information was received via fax: On July 9, the licensee's radiation safety officer called to report a potential medical event had occurred the previous afternoon. The Agency was advised that an interstitial treatment could not be completed involving a High Dose Rate afterloader (HDR) at the University of Illinois at Chicago. As a result of safety features built into the HDR's programming, the first fraction of a four fraction treatment of 300 rad was automatically terminated and the source returned to the safe/stored position after only 6 rad had been delivered when unexpected resistance was detected in the source wire as it moved to the second dwell position. Subsequent attempts to clear the path and reinitiate the treatment were unsuccessful. As a result, an underdose of 98% of the fraction occurred. The HDR unit was subsequently re-run through its quality assurance tests for positioning accuracy with no anomalies noted. The patient was notified of the event immediately.

A week before, the patient had 3 catheters surgically placed near the pelvis and their location relative to the treatment site verified by CT scan with an additional scan just before treatment was initiated. After reviewing the scan the written directive was modified to call for 18 dwell positions in three channels for a duration of 101 seconds. Four fractions were going to be completed on successive days. The scan suggested the possibility of the catheters being moved as a result of distention of some internal organs. Although the 'dummy' wire successfully traversed the initial path, and the active wire reached the first treatment position, after the initial 2 seconds of programmed dwell time, the HDR unit detected an unexpected delay in the wire moving to the second dwell position, presumably due to constriction of the pathway, and automatically retracted the active wire to the safe store position. With the assistance of the manufacturer's off site technical advisor, the error code was cleared and attempts were made to reinitiate the treatment however, the 'dummy' wire could not traverse the path and the treatment abandoned.

In this instance the device performed as designed and subsequent quality assurance tests confirmed the device was operating as expected. Although no effect on the patient is expected from the event, physicians are determining what course of treatment options are available at this time. The licensee was advised of the requirement to submit a written report of the event in accordance with the regulations. Pending additional developments and submission of the report, this matter remains open for now. The HDR Afterloader has a 5 Ci Ir-192 source and was being used to treat a cancer in the pelvic area. Illinois Report Number: IL14011 A Medical Event may indicate potential problems in a medical facility's use of radioactive materials. It does not necessarily result in harm to the patient.