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A Simple EPID-Based Tool for Dosimetric Checks On Monthly Linac QA

Y Chen

Y Chen*, J Wang , H Zhang , P Hu , J Fan , W Hu , Fudan University Shanghai Cancer Center, Shanghai, shanghai


SU-I-GPD-T-478 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This study aims to establish an electronic portal imaging devices (EPIDs) based QA tool for routine dosimetric QA.

Methods: An EPID based Automatic QA tools were developed. This tools can evaluate the flatness, symmetry, MU linearity, beam energy output, and MLC positions. During the test, the source to detector distance was set to be 100 cm and zero-degree gantry angle. All fields irradiated directly to the EPID, except two fields with simple PMMA phantom with different depths centrically placed in each field. The effectiveness and consistency of EPID-based QA were tested on a Varian Trilogy. The clinical commissioning, usage, and evaluation of this QA tool were also validated on other 3 Varian LINACs (1 Trilogy, 2 Clinac IX) over a period of six months.

Results: Beam symmetry and flatness agree well with measurements from PTW QuickCheck and SUN NUCLEAR Profiler2. Beam energy output constancy is within 1% compared with ion-chamber. The long-term slope consistency of the MU-dose curve is within 1.3%. The picket fence analyses can detect MLC positioning errors of 0.5 mm and display the relative positions distribution. The whole QA process takes less than 10 min to complete a photon beam test, MLC test and the MU linearity test.

Conclusion: The simplified EPID-based tool has been proved to be efficient and feasible for crucial daily and monthly QA test on the dosimetric parts. The high efficiency and ease of use make it suitable for implementation in cancer centers with Trilogy and IX linacs.

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