M Naessig*, K Kelly, A Alvarez, T Wagner, E Galvan, N Papanikolaou, S Stathakis, University of Texas HSC SA, San Antonio, TX

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  M Naessig

PO-GePV-T-349 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: PTW VERIQA is an independent Monte Carlo secondary dose verification system. This system was tested by evaluating the dose distribution between the approved plan and the PTW VERIQA plan by means of gamma index as well as the mean dose difference of organs at risk (OARs), and comparing these values to patient specific QA.

Methods: Sixteen stereotactic radiosurgery (SRS) treatment plans with multiple brain metastases were exported from Brainlab Elements TPS to VERIQA. Patient specific QA was performed with the PTW Octavius 4D using the 1000SRS detector array. The gamma analysis for the total volume was calculated in VERIQA and PTW VeriSoft for each treatment plan with a gamma criteria of 3%/1mm and a low-dose threshold of 10% of the maximum compared dose. The mean dose difference for left and right eyes, lens, and optic nerves, brainstem, chiasm, and PTVs were recorded from VERIQA.

Results: Each SRS treatment plan showed a gamma passing rate of at least 99% for the total volume at 3%/1mm when using VERIQA. In comparison to patient specific QA results, the absolute average percent difference between VERIQA and VeriSoft was 1.85% with a range of -1.33% to 7.86%. The mean dose difference for each PTV exhibited a range of -1.52Gy to 2.31Gy. The plans with a higher number of targets exhibited a larger absolute average PTV mean dose difference between the TPS and the verification dose. The mean dose difference for all OARs showed a range of -0.11Gy to 0.22Gy with the left optic nerve showing the largest average mean dose difference.

Conclusion: The gamma indices for the SRS QA measurements and the VERIQA Monte Carlo 3D computations were analogous. A more in depth evaluation is attainable with VERIQA by analyzing PTVs and OARs along with total volume, which is beneficial when delivering SRS treatments.

Funding Support, Disclosures, and Conflict of Interest: Funding provided by PTW to complete the following research.

Keywords

Treatment Verification, Stereotactic Radiosurgery, Quality Assurance

Taxonomy

TH- External Beam- Photons: Quality Assurance - IMRT/VMAT

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