OneIso: A Streamlined HyperArcTM Patient and Machine QA for Single-Isocenter Multi-Target (SIMT) SRS
L Skinner1*, D Capaldi2, P De Jean3, J Schulz1, P Dubrowski1, A Yu1, (1) Stanford University, Stanford, CA, (2) University of California, San Francisco, San Francisco, CA, (3) Luca Medical Systems Inc., Palo Alto, CA
Presentations
SU-E-BRA-4 (Sunday, 7/10/2022) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]
Ballroom A
Purpose: Single-isocenter multitarget (SIMT) volumetric modulated arc therapy (VMAT) is a promising approach to SRS. However, the standard quality assurance (QA) process to ensure the accuracy of treatment is complex and time-consuming. In this study, a QA phantom, OneIso©, was designed and developed to streamline machine and patient QA for HyperArc™ frameless SIMT VMAT SRS treatments.
Methods: OneIso was designed with the following features: (1) A row of off-axis ball-bearings was integrated into the phantom for off-axis Winston-Lutz (OAWL) measurements; and (2) A movable insert that can be switched between the central Winston-Lutz (WL) test target and dose measurement (film and point dose measurement) without moving the phantom itself. OneIso is indexed to the Encompass couch, requiring only one setup which begins with the couch automatically moved to the predefined location. CBCT is employed for fine adjustment of the phantom location. OAWL QA, film QA and point dose measurements were performed. Finally, in-house software developed in MATLAB® was employed to quantify the spatial accuracy versus distance from the isocenter. These results were evaluated against our institutional standard QA procedure.
Results: The proposed OneIso workflow reduces QA setup time by 60%. For both film and point dose measurements, OneIso and the solid water phantom agree within 2% for 5 cases investigated. Additional to the isocenter WL result, quantification of the spatial accuracy of a linac with the OAWL was available with the proposed phantom. With the design of the phantom mounting basket, the phantom can be operated within the HyperArcTM safety zone.
Conclusion: QA workflow was developed to streamline the QA task for brain SRS QA. OneIso substantially improves the robustness, reliability, and efficiency of QA for the clinical SRS treatments. This phantom will give clinics confidence in treating brain SRS using SIMT VMAT.
Funding Support, Disclosures, and Conflict of Interest: The authors hold a US patent for this work. Luca Medical Systems and Stanford University have a patent licensing agreement.
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