Click here to

Session: Therapy General ePoster Viewing [Return to Session]

Comparison of Monte Carlo Computed Gamma Indices and Measured Patient Specific IMRT QA Results

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


PO-GePV-T-348 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

ePoster Forums

Purpose: To evaluate differences in gamma indices reported by PTW VERIQA dose verification software and IMRT QA results measured by the PTW Octavius 4D system coupled with PTW VeriSoft dose comparison and evaluation software. The comprehensive patient QA software VERIQA has been developed to analyze parameters involved with pre-treatment patient QA using 3D Monte Carlo dose calculations.

Methods: Forty-five head and neck (HN), pelvis, and thorax VMAT (Volumetric Modulated Arc Therapy) patient plans (6 and 10 MV included) were exported from the Pinnacle treatment planning system to the VERIQA software and doses were computed using a 3D Monte Carlo calculation algorithm. Gamma indices were evaluated for each patient using 3%/2mm and 3%/1mm criteria, both with a threshold of 10% of maximum dose, using VERIQA and were compared to data measured with the Octavius 4D QA system. The average gamma value and standard deviation were calculated and reported for each criterion, as well as the average percent difference between the VERIQA and Octavius data.

Results: The average gamma values and standard deviation for VERIQA were 95.20% ± 4.02% and 93.41% ± 4.81% for 3%/2mm and 3%/1mm, respectively. For the Octavius, measurements were 96.96% ± 2.20% and 92.25% ± 4.47% for 3%/2mm and 3%/1mm, respectively. The average percent differences between the VERIQA and Octavius gamma values were 1.89% ± 4.52% and -1.24% ± 7.22% for 3%/2mm and 3%/1mm, respectively.

Conclusion: The differences in gamma indices between the Octavius 4D system and VERIQA secondary verification software were comparable for 3%/2mm and 3%/1mm criteria. VERIQA also offers the computation of other patient specific IMRT QA metrics, including secondary monitor unit verification and computation of dose and gamma values for targets and organs at risk. Thus, VERIQA allows for a comprehensive pre-treatment evaluation of patient plans.

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


Treatment Verification, Monte Carlo


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

Contact Email