The modulation transfer function (MTF) must be measured against the requirements of the specific digital imaging application under consideration in order to evaluate the performance of detector equipment and to further develop the detector by performing quality-assurance (QA) procedures. The purpose of this study was to measure the MTF in digital megavoltage images (DMVs) for radiation therapy (RT) by using an edge block. We used 6 megavolts (MVs) of energy for the pre-sampling MTF, along with a photo-stimulating phosphor-based computed radiography (CR) system and a hexalon lead screen that contained a terbium-doped gadolinium oxysulfide granular phosphor (Gd2O2S:Tb). The DMV MTF was measured at both low and high resolutions according to changes in the dose in monitor units (MUs) by using four different detector combinations: CR-IP (image plate: photo-stimulable phosphor screen), CR-IP-Lead (image plate + lead screen), CR-IP-Regular (fast front screen + image plate + fast front screen) and CR-IP-Fast (fast back screen + image plate + fast front screen). At a low resolution, the MTF 50% and the MTF 10% when using the CR-IP detector increased by about 30% and 46%, in proportion to the increase in the dose from 1 to 20 MU, respectively. At a high resolution, the CR-IP and the CR-IP-Lead detectors showed increases in the MTF of about 8% or 10% when the dose increased from 1 to 20 MU. The present study, therefore, evaluates how edge methods can be helpful in taking MTF measurements during QA tests of a megavoltage imaging (MVI) system.
Bibliographical noteFunding Information:
This study was supported by a program of the Basic Atomic Energy Research Institute (BAERI) (2009-0078390) and a grant (2012-007883) from the Mid-career Researcher Program through the National Research Foundation (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP) of Korea. Also, this work was supported by the Industrial R&D program of the Ministry of Trade, Industry and Energy (MOTIE) / Korea Evaluation institute of Industrial Technology (KEIT) [10048997, Development of the core technology for integrated therapy devices based on real-time MRI guided tumor tracking].
© 2014, The Korean Physical Society.
- Digital megavoltage images (DMVs)
- Megavoltage X-ray imaging (MVI)
- Modulation transfer function (MTF)
ASJC Scopus subject areas
- Physics and Astronomy(all)