Abstract
The objective of the work is to develop and implement an automated MC system for patient specific VMAT QA generating treatment planning system (TPS) compliant DICOM objects and including a stand-alone module for 3D analysis of dose deviations based on the normalized dose difference (NDD) method. The MC system developed is based on the EGSnrc code package with modifications [1] . The workflow consists of a number of modules connected to the TPS by means of DICOM exports and imports which are executed sequentially without user interaction. DVH comparison is performed in the TPS. In addition, MC- and TPS dose distributions are imported to the stand-alone analysis module based on the NDD formalism [2] . NDD failure maps and a pass rate for a certain threshold are obtained. 70 clinical plans are selected for analysis; 21 thorax plans, 26 prostate plans, 13 H&N plans and 10 gynecological plans. Agreement within 1.5% has been found between clinical- and MC data for the mean dose to the target volumes. The agreement is within 3% for parameters more sensitive to the shape of the DVH, e.g. D95% PTV or minimum dose to CTV. Tolerance criteria of 2%/3 mm are recommended for NDD analysis of prostate plans and 3%/3 mm for rest of the cases. Evaluation procedure is suggested where NDD analysis is the first step. For pass rate lower than 95% the evaluation continues with comparison of DVH parameters. For deviations larger than 2%, a visual inspection of the clinical- and MC dose distributions is performed. A fully automated evaluation is hindered by artefacts in the CT images, presence of contrast in the bladder, dose to air included in the target volume, interpretation of HU in rectum etc.
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