Dosimetric evaluation of MapCHECK 2 and 3DVH in the IMRT delivery quality assurance process

Based on per-field data, 3 dose-volume histogram (DVH) is designed to calculate 3-dimensional (3D) dose using patient-computed tomography (CT) for an intensity-modulated radiation therapy (IMRT) delivery quality assurance (DQA) process measured with diode detector arrays. In this study, the characteristics and suitability of 3DVH for an IMRT DQA process were evaluated by assessment of clinically applied results. The DQA plans were prepared with a 2D diode detector array (MapCHECK 2) for 20 IMRT patients (10 with head and neck cancer and 10 with prostate cancer), and the matching rate between the calculated dose and the measured dose was analyzed. The relative dose differences between the original IMRT plan and the recalculated plan by 3DVH were evaluated for tumor target and organs at risk (OARs). Confidence limits (CLs) were determined for quantification of the degree of agreement that should be expected in each DQA method. The individual CLs for DQA accuracy of 3D dosimetric evaluation in the tumor target and OARs were also calculated to evaluate the differences compared with conventional 2D-based DQA results. The matching rates were sufficient to validate the accuracy of IMRT DQA analyses and the calculated CL values were reasonable values considering the normal criteria of our institution. The 3DVH analysis generally had better matching rate than per-field measurement analysis and the CL values for OARs were better than those for the planning target volume (PTV). The usefulness of the 3DVH tool was verified for IMRT DQA from the point of view of dose evaluation in the corresponding patient's CT data. It also enables dosimetric evaluation in each important structure (PTV and OARs), which can promote more effective evaluation of DQA error in terms of tumor treatment and side effects.