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3D Dose Verification for Highly Modulated Treatments Using a Transmission Detector Array

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N Manohar

N. Manohar*, J. Rosenfield, E. Elder, and A. Dhabaan, Emory University, Winship Cancer Institute, Atlanta, GA


SU-I-GPD-T-293 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the validity of a transmission detector array and dose calculation algorithm for 3D verification of VMAT dose delivery.

Methods: An initial set of fluence measurements was made using a transmission detector during delivery of VMAT plans constructed in Eclipse for several disease sites. The collected data was input into the IBA Compass dose calculation algorithm to forward-calculate the 3D dose distributions to a phantom with an embedded MatriXX detector placed on the treatment table. The plans were then delivered to the same phantom / detector assembly in the absence of the transmission detector. The appropriate dose plane from the 3D Compass distribution was exported to the OmniPro I’mRT software for gamma comparison with the measured dose plane. Additionally, DVHs for dose distributions calculated by Compass using measured fluence were compared to the DVHs for the corresponding Eclipse calculations on patient CT data.

Results: Comparison of the dose planes from Compass with the dose planes measured using the MatriXX detector showed that, on average, > 99% of pixels had gamma values < 1.0 (3% / 3 mm criteria). The mean gamma value was 0.2, although a small region having gamma values > 1.0 was observed in a high dose gradient due to the limited sampling resolution of the MatriXX. Comparing the Compass calculated dose for a thoracic spine plan with Eclipse dose calculations, the percentage of voxels having gamma values > 1.0 was < 0.2%, and the average dose difference was < 1%. The Compass DVH calculated from the delivered plan showed excellent agreement with the corresponding Eclipse DVH.

Conclusion: The transmission detector array with Compass dose calculation algorithm provides accurate independent verification of 3D dose distributions. This system permits identification of discrepancies between the treatment plan and delivery.

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