TITLE:
Dosimetric Comparison of Amorphous Silicon EPID and 2D Array Detector for Pre-Treatment Verification of Intensity Modulated Radiation Therapy
AUTHORS:
Ayman G. Ibrahim, Ismail E. Mohamed, Hamdy M. Zidan
KEYWORDS:
IMRT, EPID, 2D Array Detector, Gamma Index, Quality Assurance
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.4,
September
28,
2018
ABSTRACT: Purpose: To
study the dosimetric characteristics of amorphous silicon Electronic Portal
Imaging Device EPID and 2D array detector for dose verification of
radiotherapy treatment plans, and the quality assurance QA testing of IMRT was investigated. Materials and methods: All measurements were done with Varian IX linear
accelerator, aSi-1000 EPID and 2D array detector. The dose linearity, reproducibility,
output factors, dose rate, SDD and response with slap phantom thickness have
been measured and compared against those measured by ion chamber. Results: The characteristics of EPID
and 2D array: the response of EPID agreed with 2D array and ion chamber 0.6cc.
EPID and 2D array showed short-term output reproducibility with SD = 0.1%. The
dose rates of 2D array SD = ±0.7%, EPID = ±0.4% compared with a 0.6 cc SD = ±0.5%. Output factor measurements for the central
chamber of the EPID and 2D array showed no considerable deviation from ion
chamber measurements. Measurement of beam profiles with the EPID and 2D array
matched very well with the ion chamber measurements in the water phantom. The
EPID is more sensitive to lower energy photons by increasing solid water
phantom thickness. The mean and standard deviation passing rates (γ%≤1) for film, 2D array and EPID for 30 IMRT fields of
five patients were 95.93 ± 0.96%, 99.05 ± 0.24%, and 99.37 ± 0.12%, respectively. Conclusion: The study shows that EPID and
2D array are a reliable and accurate dosimeter and a useful tool for quality
assurance. We found that the EPID was more accurate compared with both 2D array
and ion chamber. The gamma criterion of 3%/3
mm is the most suitable criteria for IMRT plans of QA.