(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: VMAT Commissioning on a Varian Clinac iX machine and setup of patient-specific VMAT QA using MatriXX phantom.
Methods: The VMAT planning used Pinnacle3, Version 14.0, treatment planning system. The commissioning procedure included: 1) Dose rate dependence measurement, setup of parameters, and VMAT planning; 2) Setup of patient specific VMAT QA using MatriXX – MultiCube Cruizer phantom; and 3) VMAT plan test and QA measurements. To perform patient specific 2D VMAT QA using MatriXX Phantom, angular dependence and CT image artifact of the phantom were investigated. Corrections to image artifact and angular effect of the phantom were applied to VMAT QA planning without the use of gantry angle sensor. Point dose measurement was also performed using “Cheese� phantom and A14SL 0.015 cc Slimline Microchamber.
Results: VMAT dose rate was set up in the range from 600 to 60 MU/minute. Eight VMAT plans were tested, which include the treatment sites at brain, head and neck, lung, abdomen, and pelvis. Using absolute dose comparison with VMAT QA, the average gamma pass rates (3%, 3 mm) were 94.9% (4 plans: > 95%, and other 4 plans: 91.4% - 94.4%). The VMAT QA with pass rates of 90% - 95% were mainly with large and complex volume structures, such as pelvic lesion with inclusion of pelvic and/or periaortic nodes. All VMAT QA showed excellent isodose line correlation between planned and QA measured results. The ion chamber point dose measurements differed from planned doses by average of -1.5% ± 1.3% (mean ± sd) (range: -2.7% - +0.7%).
Conclusion: VMAT commissioning and VMAT QA setup were accomplished for the patient treatment with the machine using VMAT technique.
Keywords
Commissioning, Image Artifacts, Setup Verification
Taxonomy
TH- External beam- photons: Quality Assurance - IMRT
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