Abstract
The purpose of this study was to investigate the relationship between plan parameters verified with DICOM-RT and dosimetric results for volumetric modulated arc therapy (VMAT). We investigated three treatment locations: prostate cancer (ten cases), maxillary sinus cancer (four cases), and malignant pleura mesothelioma (four cases) with treatment plans generated by a MonacoTM treatment planning system (TPS), and delivered with an Elekta SynergyTM linear accelerator. We calculated plan parameters, including gantry and multileaf collimator (MLC) positions, Monitor Units (MU), and millimeters of MLC motion per degree of gantry rotation (mm/degree), and performed quality assurance (QA) with a DICOM-RT plan verification system. We measured the VMAT dose with a two-dimensional diode array detector. The average gamma passing rate with percent dose acceptance criteria and distance to agreement criteria of 2 mm and 2% (2 mm/2%) were 97.4%, 97.8% and 92.0% for prostate cancer, maxillary sinus cancer, and malignant pleural mesothelioma, respectively. The mean 95th percentile value for DICOM-calculated mm/degree was 4.0, 5.2, and 11.1 for prostate cancer, maxillary sinus cancer, and malignant pleural mesothelioma, respectively. The gamma passing rate showed a correlation with calculated mm/degree, with a coefficient of determination (R2) of 0.60. Higher calculated mm/degree values led to increased dosimetric errors. We conclude that dose distribution calculated by a TPS is more reliable at smaller mm/degree.
Highlights
Volumetric modulated arc therapy (VMAT) is a new radiotherapy technique which allows the generation of treatment plans of similar or better quality than those for fixed-field intensity modulated radiation therapy (IMRT) while reducing treatment time per fraction [1]
Gamma passing rates using stricter gamma criteria (2%/2mm) were 97.4%, 97.8% and 92.0% for prostate cancer, maxillary sinus cancer, and malignant pleural mesothelioma VMAT deliveries, respectively
We investigated the relationship between plan parameters and dosimetric results for VMAT delivery
Summary
Volumetric modulated arc therapy (VMAT) is a new radiotherapy technique which allows the generation of treatment plans of similar or better quality than those for fixed-field intensity modulated radiation therapy (IMRT) while reducing treatment time per fraction [1].Patient-specific quality assurance (QA) for VMAT plans is important in confirming dose distribution. Various QA devices for VMAT delivery verification have recently been introduced, including a cylindrical diode array (ArcCHECKTM, Sun Nuclear Corporation, Melbourne, FL, USA), two orthogonal diode arrays (Delta4TM phantom, Scandidos, Uppsala, Sweden), an octagonal phantom (OctaviusTM, PTW, Freiburg, Germany), and a two-dimensional ionization chamber array with a gantry-mounted detector matrix to measure fluence (MatriXX/COMPASSTM, IBA Dosimetry, Schwarzenbruck, Germany) [3]-[5]. These methods do not evaluate other plan parameters, such as gantry angle or multileaf collimator (MLC) position during VMAT delivery. We consider it important to analyze plan parameters that influence dosimetric accuracy
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