A quantitative evaluation of quality control image for on-board imaging system of medical linear accelerator

Abstract

Objective To establish a quantitative evaluation of quality control image for the on-board imaging system of medical linear accelerator. Methods An MV planar image of electronic portal imaging device (EPID) is acquired by both Elekta iViewGT and Varian aS1000, and a kV planar image and cone-beam computed tomography (CBCT) images of CBCT are acquired by both Elekta X-ray volume imaging (XVI) and Varian On-board Imager (OBI). Phantoms used here included Las Vegas, TOR18FG, and Catphan504. A series of image quality indicators were evaluated by analyzing the images mentioned above using a quantitative method. Results A quantitative value was calculated to represent the contrast resolution of EPID. A modulation transfer function (MTF) to describe spatial resolution and a quantitative value representing contrast resolution were calculated for the kV planar image. As for the CBCT system, a series of quantitative results of noise, uniformity, CT value accuracy, and contrast resolution and a MTF were calculated to represent the performance of CBCT system. Conclusions Based on common phantoms, a complete set of quantitative methods to evaluate the image quality of EPID and CBCT has been developed, which could provide a very good reference for the establishment of quality control system for image-guided radiotherapy. Key words: Tomography, X-ray computed, cone beam; Quantitative method; Modulation transfer function; Quality control