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Beam-Matching Results On Three Varian TrueBeams Installed Over the Course of a Year

J Yoon1*, R Patel2 , S Sharma1 , K Yang1 , R McLawhorn2 , S Stephenson3 , Y Feng1 , (1) East Carolina Univ, Greenville, NC, (2) 21st Century Oncology, Greenville, NC, (3) Vidant Medical Center, Greenville, NC


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Having beam-matching of several linacs in a clinic helps to maintain the treatment schedule by allowing movement a patient to another available linac whenever necessary. Recently, we have commissioned three Varian TrueBeam linacs at a new cancer center including one moved from another center, having been previously installed a year prior. Results of these measurements are reported.

Methods: A Varian TrueBeam was installed in the new cancer center followed by moving a pre-existing TrueBeam (linac #2 in this study) from the old center. After half a year, a third new TrueBeam (linac #3) was installed. We have chosen the first TrueBeam installed in the new tower as a reference. All commissioning and data acquisition was performed under the supervision of the same physicist. Percentage depth dose (PDD) and beam profiles were compared against the reference linac. The beam profiles were measured at 10 cm depth and dmax for photon and electrons, respectively. In addition, R50 of electron beams were also compared. Profiles were also matched within 1% but the data was not shown in this study.

Results: The PDD measured on linac #2 and #3 showed less than 1% difference from the reference (typically within 0.5%), except 20 cm depth with 15 MV and 30x30 cm² on linac #2 which yielded 1.1%. The maximum difference in flatness was 0.6% using the 6 MeV electron beam with a field size of 25x25 cm² on linac #3. Symmetries for all energies and field sizes were less than 1%, where the target was 0%. Electron R50s shifted less than 0.8 mm for all energies when compared with the reference linac.

Conclusion: The beam parameters from the commissioning data were compared and matched to the first linac. The resulting beam parameters, profiles, and PDDs were found to be within acceptable tolerances.


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