Description of Event or Problem · 1
A MEDICAL PHYSICIST AT THE USER FACILITY CALLED NOMOS CUSTOMER SERVICE CONCERNING A RADIATION THERAPY PLAN HE WAS DEVELOPING USING THE CORVUS SYSTEM. THE USER HAD COPIED A PLAN, MADE CHANGES TO IT, THEN RE-RAN THE CHANGED PLAN IN CORVUS. HOWEVER, UPON EVALUATING THE RESULTS, THE USER OBSERVED THAT THE OUTPUT WAS IDENTICAL TO ORIGINAL PLAN DESPITE THE MODIFICATIONS. THE USER RAN THE PLAN AGAIN, AND THIS TIME RECEIVED THE OUTPUT EXPECTED, CONSISTENT WITH CHANGES MADE TO THE ORIGINAL PLAN. CUSTOMER SERVICE ASKED TO SEND A COPY OF THE PLAN TO NOMOS FOR EVAL. UPON RECEIVING THE TAPES, NOMOS ENGINEERING EVALUATED THE PLAN AND ATTEMPTED TO REPRODUCE PROBLEM WITHOUT SUCCESSS. NOMOS ENGINEERING THEN EVALUATED THE CORVUS SOFTWARE AND FOUND AN ERROR WHICH WOULD PRODUCE THE BEHAVIOR OBSERVED BY THE USER. THE CORVUS SYSTEM USED TWO PROCESSORS IN A WORKSTATION/SERVER CONFIGURATION. (THE SERVER SIDE IS KNOWN AS THE REMOTE COMPUTE ENGINE, OR RCE). THE SOFTWARE ERROR IS TRIGGERED WHEN THE CLOCK TIMES ON THE WORKSTATION AND THE RCE PROCESSORS ARE NOT SYNCHRONIZED. CORVUS TRANSFERS PLANS CREATED OR COPIED ON THE WORKSTATION TO THE REMOTE COMPUTE ENGINE (RCE) FOR PROCESSING, THEN BACK TO THE WORKSTATION ONCE PROCESSING HAS BEEN COMPLETED. A PLAN TRANSFERRED BETWEEN THE WORKSTATION AND RCE CONSISTS OF MANY FILES. NOT ALL OF THESE FILES ARE MODIFIED ON THE RCE DURING PROCESSING. WHEN THE RCE PROCESSING HAS BEEN COMPLETED, IT TRANSFERS ONLY THOSE FILES THAT HAVE BEEN MODIFIED BACK TO THE WORKSTATION. CORVUS KEEPS TRACK OF WHICH FILES WERE MODIFIED BY COMPARING TWO FILE ATTRIBUTES: FILE SIZE AND FILE DATE/TIME STAMP. IF THE TIME CLOCK ON THE WORKSTATION DOES NOT MATCH THE TIME CLOCK ON THE RCE, IT IS POSSIBLE THAT A MODIFIED FILE (THAT HAS NOT CHANGED IN SIZE) COULD BE INCORRECTLY IDENTIFIED AS UNMODIFIED BECAUSE OF THE TIME STAMP ERROR. THIS COULD ONLY OCCUR IF THE PROCESSING TIME TO MODIFY THE FILE IS PRECISELY EQUAL (TO THE HOUR, MINUTE, AND SECOND) TO THE TIME DIFFERENCE ERROR BETWEEN THE TWO TIME CLOCKS. ALSO, THE FILE MUST REMAIN EXACTLY THE SAME SIZE. WHEN THIS HAPPENS, THE CORVUS RCE INCORRECTLY IDENTIFIES THE FILE AS UNMODIFIED (BECAUSE IT SEES THAT THE TIME STAMP IS THE SAME AND THE SIZE HAS NOT CHANGED), AND DOES NOT SEND IT BACK TO THE WORKSTATION WITH THE OTHER MODIFIED FILES. AS A RESULT, THIS PARTICULAR MODIFIED FILE WILL NOT BE INCLUDED IN THE RE-PROCESSED PLAN. THE PROBABILITY OF OCCURRENCE IS REMOTE, BUT IT IS POSSIBLE AND APPEARS TO BE THE CAUSE OF WHAT THE INITIAL REPORTER OBSERVED. NORMAL CLINICAL PRACTICE INVOLVES PRACTITIONER REVIEW OF THE PLAN AS PART OF THE REQUIRED QA PROCESS. THE PLANS PRODUCED BY THE CORVUS SYSTEM INDICATE THE THERAPEUTIC DOSAGES THE PLAN WILL DELIVER, AND THE PRACTITIONER MUST COMPARE THESE TO THE PT PRESCRIPTION. HOWEVER, NOMOS IS AWARE THAT THE LEVEL OF SCRUTINY VARIES AMONG INSTITUTIONS. IF THE PRACTITIONER FAILS TO NOTICE THAT THE MODIFIED PLAN DOES NOT YIELD EXPECTED RESULTS, THE INCORRECT TREATMENT PLAN COULD BE USED FOR THERAPY. THE POTENTIAL CONSEQUENCES DEPEND ON THE DEGREE TO WHICH THE PLAN IS INCORRECT, AND RANGE FROM INSIGNIFICANT TO POTENTIAL UNDER/OVER DOSE. THEREFORE, NOMOS CREATED A FIX FOR THIS SOFTWARE ISSUE. THE FIX CHANGES THE FILE TRANSFER PROCESS BETWEEN THE CORVUS SYSTEM'S WORKSTATION AND SERVER SUCH THAT THE FILE SIZE AND TIME STAMP ARE NO LONGER EVALUATED, AND ALL FILES ARE TRANSFERRED WHETHER THEY ARE MODIFIED OR NOT. NOMOS CREATED A CUSTOMER-INSTALLABLE SOFTWARE PATCH TO IMPLEMENT THIS FIX AND SENT IT TO ALL AFFECTED CUSTOMERS. INCLUDED WAS A CUSTOMER NOTIFICATION EXPLAINING THE PROBLEM, AND A RESPONSE FORM TO SEND BACK TO NOMOS INDICATING THAT THEY HAD SUCCESSFULLY INSTALLED THE PATCH.