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On the Spatial Accuracy of Single Isocenter Multiple Brain Metastases SRS with BrainLab Elements

D Saenz*, J McCulloch , K Rasmussen , N Kirby , P Myers , S Stathakis , N Papanikolaou , University of Texas HSC SA, San Antonio, TX


(Sunday, 7/14/2019) 3:30 PM - 4:00 PM

Room: Exhibit Hall | Forum 4

Purpose: Stereotactic radiosurgery (SRS) of multiple brain metastases with a single isocenter has increased in popularity in recent years. This complex treatment technique is more sensitive to certain sources of error in the planning and treatment process than conventional SRS including setup rotation uncertainties and MRI distortion artifacts. The purpose in this study was to conduct an end-to-end test with the Lucy phantom using BrainLab Elements to determine the localization accuracy to multiple targets.

Methods: The film insert of the Lucy phantom was used as the target for this end-to-end test. The insert has four pins which mark a film upon closing the insert. A dummy film was placed in the insert and the Lucy phantom was scanned with an immobilization mask following a frameless SRS workflow. The resulting CT was planned in Brainlab Elements Multiple Brain metastases software. The four markers on the film were contoured and designated as PTVs. Each target was planned to 8 Gy with the isocenter placed at the centroid of the four targets. A non-coplanar four arc planning template was followed. The plan was treated on a Novalis Tx linear accelerator using radiochromic film with ExacTrac infrared and x-ray imaging for setup and localization. After scanning the film, the distance from the center of the dose cloud to the film mark was measured for each target as a metric of spatial accuracy.

Results: The end-to-end accuracy was determined to be 1 mm or better for all four targets. The minimum error was 0.5 mm while the maximum was 1 mm.

Conclusion: Sub-millimeter accuracy was confirmed using the Lucy phantom with BrainLab Elements indicating confidence in targeting accuracy with the increase in treatment efficiency of a single setup. Future work includes examining targets which are further from the isocenter and end-to-end dose accuracy.


Stereotactic Radiosurgery, Quality Assurance, Film


TH- External beam- photons: intracranial stereotactic/SBRT

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