(Tuesday, 7/16/2019) 1:45 PM - 3:45 PM
Room: Stars at Night Ballroom 4
Purpose: Real-time optical imaging viability as a quality assurance and verification tool for small beamlets and dynamics in SRS, SBRT, VMAT plans was investigated. The sensitivity to common delivery errors was also compared against a standard diode array QA tool.
Methods: A range of static beams and dynamic VMAT plans were simulated in a treatment planning system (TPS) and delivered to a tank filled with radio-luminescent liquid. Emission was imaged using a blue-sensitive intensifier CMOS camera time-gated to the linac. For static beams, the percentage dose depth (PDD) and cross beam profiles (CBP) were obtained and compared to TPS data. Gamma analysis was performed on all dynamic plans, and the technique was tested for sensitivity against common errors (multileaf collimator position, gantry angle) by inducing deliberate errors in VMAT plans per control point. The technique’s detection limits for spatial resolution were tested for the smallest beam size and the smallest number of control points that could be imaged reliably.
Results: The optical PDD values agreed to within 2% relative to the TPS data for small static square beams (5, 10 and 50mm2). For CBP’s, a gamma pass rate >99% was achieved for a 3%/1mm criteria. All dynamic plans passed the 3%/3mm criteria with >94% rate. Beams as small as 5mm and with a total of 50-20 Monitor Units could be reliably measured. The technique was sensitive to multileaf collimator errors down to 1mm and gantry angle errors of 1°.
Conclusion: Optical imaging can provide high resolution quality assurance compared to other QA devices used commercially. The ability to image down to 50-20 MU beamlets potentially provides image capture data at each control point within dynamic plans. The technique is sensitive to small offsets errors in gantry angles and MLC leaf positions appropriate for radiotherapy SRS, SBRT and VMAT.
Funding Support, Disclosures, and Conflict of Interest: This work has been sponsored by National Institutes of Health research grants R44 CA199681, R01 EB023909, R01 EB024498, and P30 CA 23108.
Keywords
Quality Assurance, Scintillators, Optical Imaging
Taxonomy
TH- External beam- photons: Quality Assurance - VMAT
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