Mohammad Haghparast - Department of Medical Physics, School of Medicine, Iran University of Medical Sciences, Tehran, Iran
Wrya Parwaie - Department of Medical Physics, Faculty of Paramedical Sciences, Ilam University of Medical Sciences, Ilam, Iran
Mohsen Bakhshandeh - Department of Radiology Technology, School of Allied Medical Sciences, Shahid Beheshti University of Medical Science, Tehran, Iran
Nina Tuncel - Radiation Oncology Department, School of Medicine, Akdeniz University, Antalya, Turkey
Seied Rabi Mahdavi - Department of Medical Physics, School of Medicine, Iran University of Medical Sciences, Tehran, Iran

Background: Electronic portal imaging devices (EPIDs) are applied to measure the dose and verify patients’ position.Objective: The present study aims to evaluate the performance of EPID for measuring dosimetric parameters in small photon fields.Material and Methods: In this experimental study, the output factors and beam profiles were obtained using the amorphous silicon (a-Si) EPID for square field sizes ranging from ۱×۱ to ۱۰×۱۰ cm۲ at energies ۶ and ۱۸ mega-voltage (MV). For comparison, the dosimetric parameters were measured with the pinpoint, diode, and Semiflex dosimeters. Additionally, the Monaco treatment planning system was selected to calculate the output factors and beam profiles.Results: There was a significant difference between the output factors measured using the EPID and that measured with the other dosimeters for field sizes lower than ۸×۸ cm۲. In the energy of ۶ MV, the gamma passing rates (۳%/۳ mm) between EPID and diode profile were ۹۸%, ۹۸%, ۹۵%, ۹۴%, ۹۳%, and ۹۴% for ۱×۱, ۲×۲, ۳×۳, ۴×۴, ۵×۵, and ۱۰×۱۰ cm۲, respectively. The measured penumbra width with EPID was higher compared to that measured by the diode dosimeter for both energies. Conclusion: The EPID can measure the dosimetric parameters in small photon fields, especially for beam profiles and penumbra measurements.

Computer-Assisted, Electronic Portal Imaging Device, Photons, Radiation dosimetry, Radiotherapy Planning, Small Field