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An Integrated Stereotactic Radiosurgery Quality Assurance Phantom for Dosimetry and Coincidence Verification of Multiple Positioning Systems

L Skinner1*, P Dubrowski1 , D Capaldi1 , A Yu1, (1) Stanford University Cancer Center, Stanford, CA.


(Sunday, 7/14/2019) 5:00 PM - 6:00 PM

Room: Stars at Night Ballroom 4

Purpose: Brain stereotactic radiosurgery (SRS) treatments require several specific quality assurance (QA) procedures to ensure the accurate and precise treatment delivery. The two main QA objectives, positioning and dosimetric accuracy, currently involve multiple phantom setups. In this study, the dosimetric function was integrated into the phantom that was previously developed for independent verification of each positioning system (kV, MV, CBCT, lasers, optical surface monitoring, RF-breacons) to provide simple co-alignment verification, and reduce setup errors.

Methods: The novel 3D printed phantom, named OneIso, was designed with a movable insert which can switch between the Winston-Lutz test target and the dose measurement with a pinpoint ion chamber without moving the phantom itself. A central cylinder, 6 cm in diameter with density of 1.18±0.05 g/cc provides 3.5±0.1 cm of water equivalent build-up. For dose verification with the OneIso phantom, five brain SRS clinical treatment plans with 6MV FFF were anonymized, and comparisons were made using radiochromic film and pinpoint ion chamber measurements in solid water. To further confirm the visibility of the ion chamber inside the phantom, images were taken in both OneIso phantom and a standard square solid water phantom at kV and MV x-ray energies.

Results: The dose measurements between OneIso phantom with a pinpoint ion chamber and the film measurement agree within 4%. The ion chamber measurements agree within 3% between the OneIso and the solid water phantom. The optimized size and design of the OneIso phantom resulted in the ion chamber being more visible in kV and MV setup images, compared to a standard square solid water phantom - providing more accurate placement.

Conclusion: The OneIso phantom provides improved positioning verification and accurate dosimetry suitable for SRS QA measurements. The combined nature of the OneIso phantom is expected to provide a significant increase in efficiency of SRS QA measurements.


Stereotactic Radiosurgery, Quality Assurance, Dosimetry


Not Applicable / None Entered.

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