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Quality Assurance for a Commercial Automated VMAT SRS System

Y Yuan*, R Sullivan, R Popple, Univ Alabama Birmingham, Birmingham, AL

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
Radiochromic film (RCF) has high resolution but is labor intensive and has delay between delivery and evaluation. In this study, a plastic scintillator detector (PSD) was evaluated for intracranial VMAT SRS plans since this water equivalent detector doesn’t perturb small field dose distributions.
Methods:
The PSD (W2, Standard Imaging, Madison, WI), comprised of a 1 mm x 1mm cylindrical scintillator, was placed in an acrylic phantom (StereoPHAN, Sun Nuclear Corporation, Melbourne, CA). 60 VMAT SRS plans, previously measured using RCF (EBT-XD, Ashland Global Specialty Chemicals Inc., Covington, KY), were measured using the PSD. The plans used 10MV FFF photon beam and were planned using HyperArc?? (Varian Medical Systems, Palo Alto, CA). Half of the plans were for multiple targets treated simultaneously using a single isocenter. For multiple target plans, the smallest and largest targets were measured, totaling 90 measurements. The PSD dose was compared with the corresponding location on RCF.
Results:
The equivalent target diameters ranged from 2.4 to 45 mm. The mean dose difference between RCF and PSD for all plans was 0%. For single-target plans, the mean dose difference between RCF and PSD was only 0.2%; for multi-target plans, the difference was -0.2%. In addition, no significant target size dependency was observed for equivalent target diameters less than 4 cm.
Conclusion:
This study shows that the PSD measurements have good agreement with RCF measurements for both single- and multi-target plans. PSD is suitable for patient specific QA of VMAT SRS, especially for time-sensitive cases.

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Funding Support, Disclosures, and Conflict of Interest: Funding support from Sun Nuclear Corporation and Standard Imaging

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