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KMID : 1164220150270020167
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Journal of Korean Society for Radiotherapeutic Technology
2015 Volume.27 No. 2 p.167 ~ p.174
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Evaluate the implementation of Volumetric Modulated Arc Therapy QA in the radiation therapy treatment according to Various factors by using the Portal Dosimetry
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Kim Se-Hyeon
Bae Sun-Myeong
Seo Dong-Rin
Kang Tae-Young
Back Geum-Mun
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Abstract
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Purpose : The pre-treatment QA using Portal dosimetry for Volumetric Arc Therapy To analyze whether maintaining the reproducibility depending on various factors.
Materials and Methods : Test was used for TrueBeam STxTM (Ver.1.5, Varian, USA). Varian Eclipse Treatment planning
system(TPS) was used for planning with total of seven patients include head and neck cancer, lung cancer, prostate cancer, and cervical cancer was established for a Portal dosimetry QA plan. In order to measure these plans, Portal Dosimetry application (Ver.10) (Varian) and Portal Vision aS1000 Imager was used. Each Points of QA was determined by dividing, before and after morning treatment, and the after afternoon treatment ended (after 4 hours). Calibration of EPID(Dark field correction, Flood field correction, Dose normalization) was implemented before Every QA measure points. MLC initialize was implemented after each QA points and QA was retried. Also before QA measurements, Beam Ouput at the each of QA points was measured using the Water Phantom and Ionization chamber(IBA dosimetry, Germany).
Results : The mean values of the Gamma pass rate(GPR, 3%, 3mm) for every patients between morning, afternoon and evening was 97.3%, 96.1%, 95.4% and the patient's showing maximum difference was 95.7%, 94.2% 93.7%. The mean value of GPR before and after EPID calibration were 95.94%, 96.01%. The mean value of Beam Output were 100.45%, 100.46%, 100.59% at each QA points. The mean value of GPR before and after MLC initialization were 95.83%, 96.40%.
Conclusion : Maintain the reproducibility of the Portal Dosimetry as a VMAT QA tool required management of the various factors that can affect the dosimetry.
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KEYWORD
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VMAT, Portal Dosimetry, Gamma Pass Rate, MLC
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