Film quality assurance (QA) software is an integral component of patient-specific QA (PSQA) for various radiation techniques where high degrees of geometrical and dosimetric accuracy are warranted. Evaluating the accuracy of these products has relied on various techniques ranging from comparative analyses, measurements with phantoms and other detectors along with confidence from industry-standard peer reviews. This publication aims to see if a series of virtually created film and DICOM images can be used to test the accuracy of certain PSQA metrics used in film QA software packages. The virtual images have been reverse-engineered to simulate GafChromic EBT-XD scanned tiff images and treatment planning system exported DICOM files. Each pair of images were designed to test a particular component of the software’s ability to process curve fitting, dosimetric differences (DD), distance to agreement (DTA), percentage threshold and gamma (γ) analysis. It was found that virtual film could simulate GafChromic EBT-XD scanned films and TPS DICOM planes and provide the physicist with empirical data on the accuracy of the mentioned metrics. The series of tests were also found to aid the physicist in determining optimal calibration models, validate geometric shifts and dosimetric differences and provide insight into possible lower dose penumbral differences.
HyperArc ™ is a stereotactic radiotherapy modality designed for targeting multiple brain metastases using a single isocenter with multiple non-coplanar arcs. The purpose of this study was to assess the e cacy of two patient speci c quality assurance methods, lm and the Varian Portal Dosimetry System with Varian's HyperArc ™ technique and raise important considerations in the customisation of patient speci c quality assurance to accommodate HyperArc ™ delivery. Assessment criteria included gamma analysis and mean dose at full width half maximum. The minimum met size, maximum off-axis distance and suitable energy were identi ed and validated. Patient speci c quality assurance procedures were applied to a range of clinically relevant brain met plans. Initial investigation into energy selection showed no signi cant differences in gamma pass rates using 6MV, 6MV FFF or 10MV FFF for met sizes greater than 15 mm diameter at the isocenter. Gamma pass rates (2%/2mm) for 15 mm mets at the isocenter for all energies were greater than 96.0% for portal dosimetry and greater than 98.7% for lm. Fields of size 15 mm placed at various distances (10-70 mm) from the isocenter resulted in a maximum mean dose difference of 1.5% between lm and planned. Clinically relevant plans resulted in maximum mean dose difference for selected mets of 1.0% between lm and plan and maximum point dose difference of 2.9% between portal dose and plan. Portal dose image prediction was found to be a quick and convenient quality assurance tool for mets larger than 15 mm near the isocenter but provided diminished geometrical relevance for off-axis mets. Film QA required exacting procedures but offered the ability to assess the accuracy of geometrical targeting for off-axis mets and provided dosimetric accuracy for mets to well below 15 mm diameter.
HyperArc™ is a stereotactic radiotherapy modality designed for targeting multiple brain metastases using a single isocenter with multiple non-coplanar arcs. The purpose of this study was to assess the efficacy of two patient specific quality assurance methods, film and the Varian Portal Dosimetry System with Varian’s HyperArc™ technique and raise important considerations in the customisation of patient specific quality assurance to accommodate HyperArc™ delivery. Assessment criteria included gamma analysis and mean dose at full width half maximum. The minimum met size, maximum off-axis distance and suitable energy were identified and validated. Patient specific quality assurance procedures were applied to a range of clinically relevant brain met plans. Initial investigation into energy selection showed no significant differences in gamma pass rates using 6MV, 6MV FFF or 10MV FFF for met sizes greater than 15 mm diameter at the isocenter. Gamma pass rates (2%/2mm) for 15 mm mets at the isocenter for all energies were greater than 96.0% for portal dosimetry and greater than 98.7% for film. Fields of size 15 mm placed at various distances (10–70 mm) from the isocenter resulted in a maximum mean dose difference of 1.5% between film and planned. Clinically relevant plans resulted in maximum mean dose difference for selected mets of 1.0% between film and plan and maximum point dose difference of 2.9% between portal dose and plan. Portal dose image prediction was found to be a quick and convenient quality assurance tool for mets larger than 15 mm near the isocenter but provided diminished geometrical relevance for off-axis mets. Film QA required exacting procedures but offered the ability to assess the accuracy of geometrical targeting for off-axis mets and provided dosimetric accuracy for mets to well below 15 mm diameter.
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