Description of Event or Problem · 1
A RADIATION OVERDOSE OCCURRED. THE PATIENT WAS A FEMALE WITH CARCINOMA OF THE LARYNX, WITH A PRESCRIBED COURSE OF 26 IMRT - INTENSITY MODULATED RADIATION THERAPY- TREATMENTS TO BE DELIVERED IN A TWICE-A-DAY -BID- REGIMEN. THE ACCIDENTAL OVERDOSE OCCURRED DURING THE PATIENT'S 3RD TREATMENT. THE LINEAR ACCELERATOR EQUIPMENT INVOLVED IS A VARIAN 2100CD MANUFACTURED BY VARIAN MEDICAL SYSTEMS AND INSTALLED IN 1997. THIS LINAC IS EQUIPPED WITH AN OEM COMPUTER-CONTROLLED MULTILEAF COLLIMATOR -VARIAN MILLENNIUM 120 MLC- RUNNING ON VARIAN'S 'VARIS VISION' RELEASE 7.0 SOFTWARE AND INFORMATION SYSTEM -'SYSTEM'-. SEQUENCE OF EVENTS 1- ON DAY 1 OF BID TREATMENT, THE PATIENT RECEIVED THEIR FIRST TWO TREATMENTS -BID- ACCORDING TO PLAN. PATIENT TREATED BY THERAPISTS A, B AND C. 2- ON DAY 2 OF BID TREATMENT, PATIENT RECEIVED AN ACCIDENTAL OVERDOSE ON THE 3RD TREATMENT. NOTE: AT THE TIME OF THE 3RD TREATMENT, THE TREATING THERAPIST -THERAPIST D- DID NOT PERCEIVE THAT AN OVERDOSE HAD OCCURRED. 3- THE PATIENT RETURNED TO THE RADIATION ONCOLOGY DEPARTMENT IN THE AFTERNOON OF DAY 2 TO RECEIVE HER 4TH TREATMENT. THE THERAPIST TEAM ON LINAC #1 -THERAPISTS C AND E- BEGAN TO DELIVER THE 4TH TREATMENT FRACTION TO THE PATIENT, BUT IMMEDIATELY NOTICED THAT IT HAD TAKEN ONLY 0.2 MINUTES TO TREAT THE FIRST FIELD, AND SO THEY STOPPED THE TREATMENT PROCESS TO ASCERTAIN AND VERIFY LINAC OPERATION AND MLC STATUS. DURING THEIR TROUBLESHOOTING PROCESS, THE THERAPIST TEAM NOTICED ON THE COMPUTER MONITOR DISPLAY THAT THE MLC WAS PARKED -I.E. A TOTALLY OPEN FIELD WAS BEING DISPLAYED-. THE TEAM HALTED THE TREATMENT DELIVERY PROCESS AND WENT INTO THE VARIS SYSTEM TO CHECK AND VERIFY THE INTEGRITY OF THE TREATMENT PLAN FILE. THE TREATING THERAPIST -THERAPIST C- OPENED EVERY ONE OF THE 13 FIELDS COMPRISING THE PLAN AND NOTICED THAT EACH FIELD WAS MISSING THE REQUIRED MLC PATTERNS AND HE NOTIFIED PHYSICS OF THIS SITUATION. ANALYSIS BY PHYSICS PERSONNEL CONFIRMED THAT THE FILE HAD BECOME CORRUPTED. 4- AT THIS POINT, A COMPLETE INVESTIGATION WAS INITIATED BY PHYSICS, THE RTT STAFF, AND THE ATTENDING PHYSICIAN TO ASCERTAIN AND VERIFY EXACTLY WHAT DOSE LEVEL HAD BEEN DELIVERED DURING EACH OF THE PRIOR THREE TREATMENTS. A REVIEW OF THE COMPUTER SYSTEM LOGS FOR LINAC #1 CONFIRMED THAT ALTHOUGH TREATMENTS #1 AND #2 WERE DELIVERED AS PLANNED, AN UNEXPECTED OVERDOSE WAS DELIVERED DURING THE 3RD TREATMENT DUE TO THE MLC LEAVES BEING FULLY RETRACTED AND 'PARKED,' THUS ALLOWING FULL RADIATION BEAM DELIVERY IN AN UNMODULATED -I.E. 'OPEN FIELD'- STATE. THE MAXIMUM DOSE DELIVERED TO THE SPINAL CORD WAS ESTIMATED TO BE 850 CGY INSTEAD OF THE PRESCRIBED 150 CGY. 5- UPON COMPLETION OF THE INTERNAL INVESTIGATION, THE PATIENT'S APPROVED TREATMENT PLAN WAS REVIEWED AND MODIFIED BY THE ATTENDING PHYSICIAN TO ACCOUNT FOR THE ADDITIONAL, UNEXPECTED DOSE DELIVERED TO THE SPINAL CORD DURING THE 3RD TREATMENT. THE PATIENT WAS INFORMED OF THE SOFTWARE MALFUNCTION AND THE DOSING ERROR. NEW TREATMENT PLANS WERE DEVELOPED THAT DID NOT INCLUDE THE SPINAL CORD IN THE TREATMENT FIELD, TO REDUCE THE POSSIBILITY OF A SPINAL CORD COMPLICATION. THE NEW TREATMENT PLAN WAS REVIEWED AND APPROVED BY THE ATTENDING PHYSICIAN. CAUSE OF EQUIPMENT FAILURE: OUR RETROSPECTIVE INVESTIGATION CONFIRMED THAT THE TREATMENT PLAN FILE HAD BECOME CORRUPTED BETWEEN THE 2ND AND 3RD TREATMENT, WHEN THERAPIST C ATTEMPTED TO UPDATE THE VARIS DATABASE FILE, RE-ASSIGNING THE PATIENT FROM LINAC #2 TO LINAC #1. WE BELIEVE THE FILE CORRUPTION OCCURRED SOME TIME AFTER THE 2ND TREATMENT, SINCE OUR INVESTIGATION REVEALED THAT THE TREATING THERAPIST -THERAPIST C- HAD EXPERIENCED DIFFICULTY UPDATING THE DATABASE FILE. THERAPIST C ATTEMPTED TO PERFORM THIS DATABASE FILE UPDATE WHILE IN THE SYSTEM'S 'RT CHART' SOFTWARE MODULE. IN THE COURSE OF ATTEMPTING TO PERFORM A "FILE SAVE" FOR THE TRANSFERRED FILE AND EXITING THE RT CHART MODULE, THE SYSTEM'S COMPUTER SCREEN FROZE UP AND THE SYSTEM DID NOT VERIFY A SUCCESSFUL FILE TRANSFER. THIS OVERDOSE OCCURRED -- IN PART -- DUE TO THE LACK OF A 'FAILSAFE' MECHANISM -SOFTWARE INTERLOCK- IN THE LINAC TO PREVENT FULL RADIATION BEAM DELIVERY WHENEVER THE LINAC'S MLC SHAPE IS NOT PROPERLY SET AND CONFIGURED IN THE RADIATION FIELD. THE ABILITY OF THE LINAC TO DELIVER A FULL BEAM THROUGH AN OPEN FIELD IS INCONSISTENT WITH FAILSAFE DESIGN PRINCIPLES FOR THE LINAC'S "RECORD AND VERIFY" SOFTWARE SYSTEM. IN THIS SPECIFIC CASE, A SYSTEM SOFTWARE "CRASH" DURING AN ATTEMPTED DATABASE FILE UPDATE WAS THE ROOT CAUSE AND POINT OF ORIGIN FOR THE CORRUPTED MLC CONTROL FILE -TREATMENT PLAN FILE-. THE SUBSEQUENT FAILURE OF THE LINAC'S RECORD AND VERIFY SOFTWARE TO DETECT AND PREVENT USE OF THE CORRUPTED MLC FILE ALLOWED THE LINAC TO DELIVER RADIATION BEAM IN AN OPEN -UNMODULATED- FIELD TO THE PATIENT. OUR INVESTIGATION REVEALED THAT ALL 13 TREATMENT FIELDS IN THE TREATMENT PLAN WERE CORRUPTED IN SUCH A WAY THAT THE ASSOCIATION IN THE FILE TO AN MLC WAS ERASED AND THEREFORE COULD NOT BE USED, EVEN THOUGH THE SEQUENCE OF DYNAMIC MLC LEAF MOTION CONTROLS DEFINING THE IMRT DELIVERY WAS STILL PRESENT. THE TREATMENT MACHINE -LINAC- SOFTWARE INTERPRETED THIS AS AN OPEN FIELD AND PARKED THE MLC OUTSIDE OF THE FIELD. CLEARLY AN MLC CONTROL FILE WAS ATTACHED TO THE TREATMENT FIELDS IN THE VARIS SYSTEM BUT THIS FILE WAS NOT USED FOR PATIENT TREATMENT. THE LINAC RECORD AND VERIFY SOFTWARE DID NOT HAVE A FAILSAFE OPERATING LOGIC TO PREVENT SUCH RADIATION BEAM ACTIVATION WHEN AN OPEN FIELD WAS DETECTED.