DETECTION OF SYSTEMATIC-ERRORS IN EXTERNAL RADIOTHERAPY BEFORE TREATMENT DELIVERY

The execution of an independent control of monitor units (MU) and dose distribution calculation, together with a check of the data reported in the treatment chart is an effective tool in strongly reducing the o ccurrence of systematic errors before treatment delivery. In this pape r we report the results of the analysis of 6272 controls (about 5000 p atients) registered over more than 5 years; 70 serious errors (produci ng a deviation larger than 5% from the prescribed daily dose) and 147 minor errors were detected and corrected before the start of the treat ment. The error rate was found to be strongly operator-dependent (seri ous error rate ranging from 0.3 to 2.5% when considering different ope rators). A time-trend analysis showed a significant reduction of serio us errors, i.e. 1.5% in the period from September 1991 to April 1994 c ompared to 0.9% in the period from April 1994 to November 1996. Howeve r, even if the double check was highly effective in revealing human er rors, three serious systematic errors (errors occurring during the cal culation/planning/transcription phases) escaped the control and were d etected by diode in vivo dosimetry during the period October 1994 to N ovember 1996 (in 650 patients controlled). (C) 1997 Elsevier Science I reland Ltd.