Abstract
Purpose: he purpose of this study is to evaluate and implement a digital IMRT quality assurance (QA) procedure for patient-specific volumetric dose using commercially available products. Dose distributions generated from a treatment planning system (TPS) were delivered and analyzed with dose-volume-histogram (DVH) analysis software. Methods: The MapCheck2 device along with 3DVH (Sun Nuclear, Melbourne, FL) software was studied for IMRT QA capabilities. All manufacturer specifications were followed in order to properly set up the diode array device for accurate absolute dose measurements. Planar dose maps were generated by the Pinnacle3 TPS (Philips Medical Systems, Andover, MA) for field-by-field IMRT QA analysis. Also exported from patient plans were RT dose, RT plan, RT structure, and CT data DICOM files. Dose delivery was done using a step-and-shoot, en-face technique onto the MapCheck2 device. After measured-vs-calculated planar dose analysis for each beam, a planned-dose-perturbation (PDP™) file was generated. This PDP file allows the software to manipulate the TPS-calculated dose distributions to include actual measured dose differences from a phantom onto a patient CT-dataset. These dose perturbations are then able to be observed through differences of a TPS-calculated DVH and a measured-DVH within the 3DVH software. Simple tests were performed to assess MapCheck2 performance and 3DVH sensitivity to errors. Results: All planar dose measurements in this study have met the clinical tolerance of 3% absolute dose/3mm gamma analysis. For volumetric analysis, the 3D results comparing planned-vs-delivered matching doses (gamma criterion of 3%/3mm) were 99.3% and 98.2% for a rectum and prostate plan, respectively. Measurements with introduction of intentional errors produced reasonable results when analyzing dose to critical structures with DVHs. Conclusion: The implementation of a digital QA procedure will facilitate a more efficient workflow for physicists with the added benefit of a patient-specific volumetric dose analysis for physicians.
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