The aim of this study is to introduce tools to improve the security of each IMRT patient treatment by determining action levels for the dose delivery process. To achieve this, the patient-specific quality control results performed with an ionization chamber-and which characterize the dose delivery process-have been retrospectively analyzed using a method borrowed from industry: Statistical process control ͑SPC͒. The latter consisted in fulfilling four principal well-structured steps. The authors first quantified the short term variability of ionization chamber measurements regarding the clinical tolerances used in the cancer center ͑Ϯ4% of deviation between the calculated and measured doses͒ by calculating a control process capability ͑C pc ͒ index. The C pc index was found superior to 4, which implies that the observed variability of the dose delivery process is not biased by the short term variability of the measurement. Then, the authors demonstrated using a normality test that the quality control results could be approximated by a normal distribution with two parameters ͑mean and standard deviation͒. Finally, the authors used two complementary tools-control charts and performance indices-to thoroughly analyze the IMRT dose delivery process. Control charts aim at monitoring the process over time using statistical control limits to distinguish random ͑natural͒ variations from significant changes in the process, whereas performance indices aim at quantifying the ability of the process to produce data that are within the clinical tolerances, at a precise moment. The authors retrospectively showed that the analysis of three selected control charts ͑individual value, moving-range, and EWMA control charts͒ allowed efficient drift detection of the dose delivery process for prostate and head-and-neck treatments before the quality controls were outside the clinical tolerances. Therefore, when analyzed in real time, during quality controls, they should improve the security of treatments. They also showed that the dose delivery processes in the cancer center were in control for prostate and head-and-neck treatments. In parallel, long term process performance indices ͑P p , P pk , and P pm ͒ have been analyzed. Their analysis helped defining which actions should be undertaken in order to improve the performance of the process. The prostate dose delivery process has been shown statistically capable ͑0.08% of the results is expected to be outside the clinical tolerances͒ contrary to the head-and-neck dose delivery process ͑5.76% of the results are expected to be outside the clinical tolerances͒.
http://www.emeraldinsight.com/10.1108/13552510910997715 Special Issue: International Conference on Industrial Engineering and Systems Management (IESM '07), Beijing, China. Guest Editor(s): Philippe Castagliola and AbdelHakim ArtibaInternational audienceAbstract - Purpose – The purpose of this paper is to evaluate and improve the quality and the reliability of pre-treatment quality controls of an efficient technique of radiotherapy called IMRT (intensity-modulated radiation therapy). The aim is then to determine if the controls can be safely reduced while keeping an optimal level of quality. Design/methodology/approach – The statistical process control method (SPC) was applied to quality assurance in IMRT. In order to characterize prostate and head-and-neck treatment process variability, individual value control charts and moving-range control charts were established. Findings – Control charts showed that prostate and head-and-neck treatment processes are only subject to random causes of variability, which means they are statistically controlled. It was proved that both processes are statistically stable and capable. Originality/value – The paper shows that SPC is an efficient method to objectively determine if quality controls can be reduced
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