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An integrated quality assurance phantom for frameless single-isocenter multitarget stereotactic radiosurgery
Dante P I Capaldi1,2, Lawrie B Skinner1,2, Piotr Dubrowski1
1Department of Radiation Oncology, School of Medicine, Stanford University, Stanford, CA, United States of America.
Physics in Medicine and Biology
|April 3, 2020
Summary
A new phantom, OneIso, streamlines quality assurance for single-isocenter multitarget brain stereotactic radiosurgery (SRS). It accurately measures off-axis accuracy and dose, ensuring treatment precision and identifying limitations for frameless SRS programs.
Area of Science:
- Medical Physics
- Radiation Oncology
- Quality Assurance
Background:
- Single-isocenter multitarget stereotactic radiosurgery (SRS) requires stringent quality assurance (QA) for accurate treatment delivery.
- Quantifying off-axis accuracy of linear accelerators is critical for these advanced SRS techniques.
- Existing QA methods can be cumbersome, necessitating streamlined approaches for frameless SRS programs.
Purpose of the Study:
- To develop and validate a novel integrated phantom for comprehensive SRS QA.
- To enable efficient verification of positioning systems, off-axis accuracy, and dosimetric accuracy in a single setup.
- To facilitate the implementation of frameless single-isocenter, multitarget SRS programs.
Main Methods:
- A 3D printed phantom, 'OneIso', was designed with a movable insert for seamless switching between Winston-Lutz tests and dose measurements.
- Independent verification of positioning, off-axis Winston-Lutz tests, and dosimetric accuracy (point dose and film) were performed without repositioning the phantom.
- Ten clinical SRS plans were delivered using 10 MV FFF beams on a Varian TrueBeam with HD-MLC; measurements were compared against solid water phantoms.
Main Results:
- The OneIso phantom demonstrated agreement within 1% with solid water phantoms for both film and point dose measurements.
- OneIso identified a decrease in spatial accuracy with increasing distance from the isocenter, exceeding tolerances at 7 cm.
- The phantom quantified off-axis spatial discrepancies, revealing limitations for multitarget SRS planning.
Conclusions:
- The OneIso phantom offers a streamlined, single-setup workflow for frameless linac-based SRS QA.
- It effectively quantifies off-axis accuracy, crucial for ensuring the safety and efficacy of single-isocenter multitarget SRS.
- This validated phantom aids in establishing maximum target distances to meet SRS accuracy guidelines.
