RAD SOURCE/RS 3000

Description of Event or Problem

IN 2002, THE REGULAR QUALITY ASSURANCE PROGRAM IDENTIFIED A POTENTIAL PROBLEM IN ONE RS 3000 BLOOD IRRADIATOR RELATED TO LOW RADIATION OUTPUT OF THE LOWER X-RAY TUBE. THE UNIT WAS IMMEDIATELY TAKEN OUT OF SERVICE. THE DATE AFTER RAD SOURCE RECEIVED THE DOSIMETRY RESULTS FROM THE QA PROGRAM, A COMPANY PHYSICIST WAS ON SITE INVESTIGATING THE UNIT. THE LOW RADIATION OUTPUT WAS CONFIRMED. THIS PROBLEM WAS NOT DETECHED BY THE TUBE CURRENT SENSING FUNCTION OF THE CONTROL SYSTEM. THE CURRENT THROUGH THE TUBE IS NORMAL. THE LOW OUTPUT APPEARS TO BE DUE TO SOME INTERNAL DEFECT IN THE TUBE. THE PROBLEM WAS NOT DETECTED BY THE RAD-SURE XR IRRADIATION INDICATORS ROUTINELY USED BECAUSE THE INDICATORS (WHICH DETECT ONLY 15 GY) WERE PLACED ON THE CENTER OF THE BLOOD BAG ON THE TOP SIDE OF THE CANISTER, CLOSEST TO THE FUNCTIONING TUBE. THIS POINT RECEIVED A DOSE OF 15 GY. THE DOSE DEFICIENCY OCCURRED ON THE BOTTOM SIDE AT THE PERIPHERY OF THE CANISTER, CLOSEST TO THE MALFUNCTIONING TUBE. BECAUSE THE IRRADIATION INDICATOR WAS PLACED IN THE CENTER OF THE CANISTER, IT RECEIVED A SUFFICIENT DOSE, WHILE THE PERIPHERY OF THE CANISTER DID NOT.