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A Comparison of Three IMRT Quality Assurance (QA) Systems: PTW Octavius4D with a 1000 Detector Array, PTW Octavius4D 1500 Detector Array and ScandiDos Delta4 Phantoms for SBRT Lung Treatments

K Fischer1*, H Parenica2 , D Defoor3 , S Stathakis4 , (1) University of Texas Health, San Antonio, TX, (2) University of Texas Health, San Antonio, TX, (3) Texas Oncology - Longview, Tyler, TX, (4) University Of Texas Health, San Antonio, TX


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To evaluate three IMRT QA systems: the PTW Octavius4D system with the 1000 detector array, the PTW Octavius4D system with the 1500 detector array and the ScandiDose Delta4 to determine which system is best suited for QA of SBRT lung plans.

Methods: QA plans for each device were created in Pinnacle for five patients who had previously undergone SBRT lung treatments. Treatment plans were then delivered to each device. The measured beams were then compared to the treatment plans using gamma analysis in the appropriate software, ScandiDos for the Delta4 and Verisoft for the PTW Octavius 1000/1500. The PTW Octavius 1000 detector array was analyzed using a 1 mm distance-to-agreement (DTA) and 3% dose difference (DD). The PTW Octavius 1500 and ScandiDos Delta4 measurements were evaluated using 3%/1mm and 3%/2mm DD and DTA criteria, respectively. The resulting gamma analyses and histograms were then compared amongst the patient QA devices.

Results: The gamma analysis passed (>90%) using both the Octavius 1000 array and the Delta4. Three out of five patients failed the analysis with the Octavius 1500 array when analyzed using 3%/1mm DD and DTA. Although most of the measurements passed the gamma analysis for each system, the histograms for each measurement reflect a higher frequency of pixels closer to a gamma of zero when using the PTW Octavius 1000 compared to the two other devices.

Conclusion: All three systems provide a good method for SBRT lung QA however, the Octavius4D system with the 1000 detector array results in histograms with a higher frequency of pixels as the gamma approaches zero.


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