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Clinical Evaluation of Portal Dosimetry Ion Chamber Array and Mobius 3D for FiF Breast IMRT QA

S Wang1*, S Gill2, R Wynn3, M Huq4, S Wang5, (1) UPMC Hillman Cancer Center at Erie, Erie, PA, (2) University of Pittsburg Medical College UPMC Hillman Cancer Center, Erie, PA, (3) Loyola University Chicago, IL, (4) UPMC Hillman Cancer Center and University of Pittsburgh School of Medicine, Pittsburgh, PA, (5) UPMC Hillman Cancer Center at Erie, Erie, PA

Presentations

PO-GePV-P-47 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: The purpose of this study is to compare the Gamma analysis between Portal Dosimetry QA (PDQA), Ion chamber based 2D-array (Matrixx) and Mobius 3D for Field-in-Field (FiF) left breast IMRT. Motivation to pursue this study is to find easier way reference for point dose calculation compatible in RadCalc for secondary check. We decided to perform the secondary check with Gamma analysis comparison between Mobius3D, PDQA and 2D array, to determine the optimal clinical QA procedure.

Methods: We evaluated number of left sided breast FiF IMRT plans. QA plans were calculated for 2D array and Varian Portal Dosimetry software (using portal dose image prediction module) and were delivered on a Varian linac. Also Plans were exported to Mobius3D software for Gamma analysis. Gamma criteria (3%/3mm >95%) was utilized for all the data analysis: OmniPro software for Matrixx; Varian software for PDQA and Mobius 3D.

Results: For composite plans, Mobius 3D, PDQA & 2D-array Gamma analysis, average 3%/3mm Gamma is more than the passing criteria of 95%. For Mobius 3D, average Gamma (3%/3mm) is 99.2%. For Portal dosimetry average Gamma is 100%. For 2D array, average Gamma is 95.64%. All three software’s results were in the same trends for passing rate. Per field Gamma analysis were performed for PDQA and 2D array. Average Gamma for per field comparison for 2D array is 91.54 % and for PDQA is 94.08 %.

Conclusion: Mobius 3D, 2D array and PDQA can all be used with satisfactory results for the secondary plan check for FiF breast IMRT QA. For the composite plans, PDQA results shown 100% passing rate. Mobius 3D results are comparable with Portal Dosimetry, and Ion chamber based 2D array is more sensitive to the plan as of resolution. From our analysis, PDQA and Mobius are equally optimal for this QA task.

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