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Treatment Planning System and Beam Data Validation for a Novel Self-Shielded Stereotactic Radiosurgery System (SRS)

S Srivastava1*, S Jani1 , D Pinnaduwage1 , X Yan1 , M Bodduluri2 , S Sorensen1 , (1) Barrow Neurological Institute (BNI) St. Joseph's Hospital & Medical Center, Phoenix, AZ, (2) Zap Surgical Systems, Inc., San Carlos, CA


(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.


Stereotactic Radiosurgery, Treatment Techniques, Validation


TH- External beam- photons: intracranial stereotactic/SBRT

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