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Program Information

Efficient and Enhanced QA Testing of Linear Accelerators Using a Real-Time Beam Monitor

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J Jung

J Jung1*, M Farrokhkish1 , B Norrlinger1 , Y Wang1 , R Heaton1, 2 , D Jaffray1, 2 , M Islam1, 2 , (1) Princess Margaret Cancer Centre, Toronto, Ontario, (2) University of Toronto, Toronto, Ontario

Presentations

SU-E-T-354 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall


Purpose:To investigate the feasibility of performing routine QA tests of linear accelerators (Linac) using the Integral Quality Monitoring (IQM) system. The system, consisting of a 1-D sensitivity gradient large area ion-chamber mounted at the collimator, allows automatic collection and analysis of beam data.

Methods:The IQM was investigated to perform several QA constancy tests, similar to those recommended by AAPM TG142, of a Linac including: beam output, MLC calibration, beam symmetry, relative dose factor (RDF), dose linearity, output as a function of gantry angle and dose rate. All measurements by the IQM system accompanied a reference measurement using a conventional dosimetry system and were performed on an Elekta Infinity Linac with Agility MLC. The MLC calibration check is done using a Picket-Fence type 2x10cm² field positioned at different off-axis locations along the chamber gradient. Beam symmetry constancy values are established by signals from an 4x4cm² aperture located at various off-axis positions; the sensitivity of the test was determined by the changes in the signals in response to a tilt in the beam. The data for various square field sizes were used to develop a functional relationship with RDF.

Results:The IQM tracked the beam output well within 1% of the reference ion-chamber readings. The Picket-Fence type field test detected a 1mm shift error of one MLC bank. The system was able to detect 2.5% or greater beam asymmetry. The IQM results for all other QA tests were found to agree with the reference values to within 0.5%.

Conclusion:It was demonstrated that the IQM system can effectively monitor the Linac performance parameters for the purpose of routine QA constancy tests. With minimum user interactions a comprehensive set of tests can be performed efficiently, allowing frequent monitoring of the Linac.

Funding Support, Disclosures, and Conflict of Interest: The presenting author's salary is funded by the manufacturer of the QA device. All the other authors have financial interests with the commercialization of this QA device.


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