Six Sigma Quality and Delivery of Radiation Therapy

Abstract

Purpose: The Six Sigma system of quality assurance has contributed to improvements in the engineering and manufacturing industries. This scale illustrates the extent to which a given process fails to perform in parts per million events. If an event is performed hundreds or thousands of times, a small percentage variance can represent a large number of errors. Six Sigma, which represents an error rate of 3.4 per million events, is considered to represent “world class” performance. Given the importance of delivering accurate and precise external radiation treatments to cancer patients, it may be appropriate for radiation oncology services to strive to meet the Six Sigma standard. This report reviews the Naval Medical Center San Diego's quality results in a Six Sigma construct. Methods: Data were collected retrospectively from monthly quality assurance reports generated from January, 1997, to August, 2001. Delivery of individual treatment portals was chosen as the quality indicator; this resulted in a sample size of 100,694 events in the 56 month period. Treatment errors were tallied, with the same error repeated over multiple treatments counted as multiple errors. Errors in treatment were classified as “RMS” or “non-RMS”: RMS errors were those errors that should have been avoided given capabilities of the RMS record and verify system. Non-RMS errors encompassed treatment variances that the RMS system could not alert the therapist to, even with the correct use of the system to its full capabilities. Results: There were 56 treatment variances noted over this period. Non-RMS errors occured at over 4 times the rate of RMS errors (46 vs. 10 events), and all variances recorded were the result of human error. RMS human errors occurred with a frequency of 99.3 events per million, and non-RMS errors with a frequency of 457 per million. No variance occurred as the result of any malfunction of the record and verify system. Conclusions: Six Sigma is a reasonable goal for active radiation oncology services. Such a focused examination of practice will identify areas of potential improvement.