Tolerance design of patient-specific range QA using the DMAIC framework in proton therapy.

Purpose: To implement the DMAIC (Define-Measure-Analyze-Improve-Control) can be used for customizing the patient-specific QA by designing site-specific range tolerances. Methods: The DMAIC framework (process flow diagram, cause and effect, Pareto chart, control chart, and capability analysis) were utilized to determine the steps that need focus for improving the patient-specific QA. The patient-specific range QA plans were selected according to seven treatment site groups, a total of 1437 cases. The process capability index, C-pm was used to guide the tolerance design of patient site-specific range. Results: For prostate field, our results suggested that the patient range measurements were capable at the current tolerance level of +/- 1 mm in clinical proton plans. For other site-specific ranges, we analyzed that the tolerance tends to be overdesigned to insufficient process capability calculated by the patient-specific QA data. The customized tolerances were calculated for treatment sites. Control charts were constructed to simulate the patient QA time before and after the new tolerances were implemented. It is found that the total simulation QA time was decreased on average of approximately 20% after establishing new site-specific range tolerances. We simulated the financial impact of this project. The QA failure for whole process in proton therapy would lead up to approximately 30% increase in total cost. Conclusion: DMAIC framework can be used to provide an effective QA by setting customized tolerances. When tolerance design is customized, the quality is reasonably balanced with time and cost demands. (c) 2017 American Association of Physicists in Medicine