14 Study and characterization of ArcCheck in tomotherapy patient specific quality control

Introduction The aim of this study is to evaluate quality controls (QC) of tomotherapy patient treatments using the ArcCheck (Sun Nuclear Corporation) diode array detector. Although many recent studies have demonstrated the dosimetric accuracy and the ability of this detector, better understanding of parameters that may influence treatment plans acceptability is required. In this frame, retrospective statistical analysis is required in order to characterize and quantify the statistical variability of QC measurements relative to the clinical tolerances. Methods QC were acquired using the ArcCheck detector [1] (Model 1220) on the clinical plans delivered using two tomotherapy units (TomoTherapy – Accuray). SNC Patient v.6.7.2 software was used to measure the dosimetric differences between the measured dose distribution and the dose calculated in the TPS using the gamma index analysis. Retrospective statistical analysis based on the statistical process controls (SPC) tools is presented [2] . Results This works presents the preliminary steps required to implement SPC tools for the retrospective statistical analysis of the patient specific QC of tomotherapy treatments. The determination of the measurement system ability (ArcCheck diode array) is presented, as well as the characterization of the measurement uncertainty depending on the treatment plan localization. Conclusions The determination of the dose delivery process performance using the SPC method should enable to optimize the QC conditions and evaluate the possibility to reduce patient quality control measurements, while maintaining safe treatment conditions to patients.