SU-E-T-354: Efficient and Enhanced QA Testing of Linear Accelerators Using a Real-Time Beam Monitor

Journal Article · Mon Jun 15 04:00:00 EDT 2015 · Medical Physics

DOI:https://doi.org/10.1118/1.4924715· OSTI ID:22548404

Jung, J; Farrokhkish, M; Norrlinger, B; Wang, Y ^[1]; Heaton, R; Jaffray, D; Islam, M ^[1]

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1. Princess Margaret Cancer Centre, Toronto, Ontario (Canada)

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 2×10cm{sup 2} field positioned at different off-axis locations along the chamber gradient. Beam symmetry constancy values are established by signals from an 4×4cm{sup 2} 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. 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.

• OSTI ID: 22548404
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 6 Vol. 42; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

07 ISOTOPE AND RADIATION SOURCES
60 APPLIED LIFE SCIENCES
APERTURES
ASYMMETRY
BEAM MONITORS
BEAMS
CALIBRATION
COLLIMATORS
COMMERCIALIZATION
DOSE RATES
DOSIMETRY
ERRORS
FIELD TESTS
IONIZATION CHAMBERS
LINEAR ACCELERATORS
PARTICLE TRACKS
QUALITY ASSURANCE
RADIATION DOSES