(Monday, 7/15/2019) 7:30 AM - 9:30 AM
Room: Stars at Night Ballroom 1
Purpose: To validate the treatment planning system (TPS) accuracy of ZAP-X (Zap Surgical, Inc.) SRS system through nondosimetric, dosimetric, and end-to-end (E2E) tests.
Methods: A comprehensive set of TPS validation tests were developed using published guidelines (TG-53, MPPG5a, TRS430). Equipment included CatPhan-500, Lucy 3D phantom, PTW MP3-XS water tank, PTW PinPoint and Exradin A16 ion chambers (IC), solid-water with 1cm high/low density slabs, and GafchromicTM EBT3 film. Nondosimetric validation included import/export, image registration (CT-CT/CT-MR), and structure/contouring/geometrical tests. Dosimetric validation included comparisons between TPS and water tank/solid-water measurements and E2E. RadCalc was used for independent MU verification. MD Anderson SRS head and RTsafe gel phantoms were used for absolute dose verification.
Results: Tools for image transfer/registration, contouring, and TPS display were functional. Slice thickness and distance accuracy was within 0.1mm, and volume accuracy was within 0-0.11cc. TPS volume measurement uncertainty was within 0.1-0.4cc. Point-dose measurements in water agreed to within ±2% for cone sizes 10-25mm, and ±1.1-5% for 7.5mm, across multiple depths from dmax (7mm) to 150mm. TPS and RadCalc agreed to within ±4% (average difference: ±1.3%) for all cone sizes (4-25mm). In homogeneous solid-water, point-dose measurements agreed to within ±4% for cones sizes 7.5-25mm. With 1cm high/low density inserts, measurements were within ±4.2% for cone sizes 10-25mm. Film-based E2E using 4mm/5mm cones resulted in gamma pass rate (GP) of 99.8% (2%/1.5mm). Lucy phantom IC dose measurements using 36 beams distributed along three non-coplanar arcs agreed to within ±4% for cone sizes 10-25mm. MD Anderson head phantom yielded passing results, with 4% TLD agreement and GP of 95%/93% (5%/3mm) for coronal/sagittal film planes. The RTsafe gel phantom gave GP of >95% (5%/2mm) for all four targets.
Conclusion: Point-dose and planar measurements are in agreement with TPS calculations for multiple phantoms and setup geometries, validating the beam model for clinical use.
Keywords
Stereotactic Radiosurgery, Treatment Techniques, Validation
Taxonomy
TH- External beam- photons: intracranial stereotactic/SBRT
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