FF and FFF patient specific QA using new Varian aS1200 portal imager and compare with PTW Octavius 1500
Keywords:
aS1200 EPID, Patient specific QA, PTW Octavius 1500Abstract
Background: An electronic portal imaging device (EPID) is an effective tool for patient specific quality assurance (QA) because of its performance and user-friendly. However, signal saturation can occur when using imager in high dose rate range, especially in flattening filter free (FFF) beams. Objective: To investigate a new Varian EPID (aS1200) with Portal Dosimetry implementation for patient specific QA in FF and FFF beams with a new gamma index criteria, which proposed by AAPM TG-218, and compared the result with PTW Octavius 1500 with PTW Octavius 4D system. Materials and methods: Randomly selected thirty patient’s VMAT plans were recalculated into sixty plans by the other beam mode using Eclipse TPS (V.13.6). Therefore, sixty plans were composed of thirty FF plans and thirty FFF plans in various tumor sites and applied for patient specific QA implementation by aS1200 EPID and PTW Octavius 1500. Gamma index criteria from AAPM TG-119 (global normalization with 3% DD/3 mm DTA and 10% low dose threshold) and AAPM TG-218 (global normalization with 3% DD/2 mm DTA and 10% low dose threshold) were applied for result interpretation. Results: In FF and FFF plans, the results showed most of the percent gamma passing rate of aS1200 EPID were slightly lower with higher SD than PTW Octavius 1500, except in stringent criteria for FFF plans. According to the AAPM TG-119, the mean gamma passing rate of aS1200 EPID and PTW Octavius 1500 was 99.02% ± 1.60% and 99.80% ± 0.52%, respectively. For AAPM TG-218, the results of aS1200 EPID and PTW Octavius 1500 was 98.36% ± 2.50% and 98.66% ± 1.86%, respectively. Conclusion: The results of the study revealed that both systems showed comparable results for a new gamma criteria. Both systems can be used as alternative detectors for patient specific QA.
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