SU‐FF‐J‐103: Performance of the Nucletron Simulix Evolution Flat‐Plate Imaging System and CBCT

Abstract

Purpose: To characterize the performance of the flat‐plate imaging system available on a commercial radiotherapy simulator, to describe some of it's clinical limitations and to present preliminary results when used in cone‐beam CT mode. Method and Materials: Measurements were performed on the Nucletron Simulix Evolution simulator installed at our institution. The Simulix Evolution is equipped with a 40 cm × 40 cm flat‐panel detector. Low contrast measurements were performed with a CDRAD contrast‐detail phantom at the center of varying‐thickness slabs of water‐equivalent material. Cone‐beam CT (CBCT) images were obtained with the AAPM CT and with a 20‐cm diameter water phantoms. Results: The Simulix Evolution performs digital fluoroscopy at a fixed rate of 3 frames/sec. There is no digital radiography mode available currently. In fluoroscopy, two automatic brightness settings are available (ABS1 and ABS2). Entrance skin exposure levels at time of acceptance exceeded 15 R/min. Contrast‐detail measurements with 10‐cm and 20‐cm water‐equivalent phantoms demonstrated that the grid has limited clinical utility since the large air gap present reduces the impact of scatter. Removing the grid reduces patient exposure by a factor of 2. Note that the grid is not used in CBCT. Evaluation of the CBCT mode demonstrated that the system does not currently meet the HU uniformity target of +/− 75 HU for water set by the manufacturer. Ring artifacts are also present and compromise clinical utility. Images and clinical examples will be presented. Conclusion: Lack of a digital radiography mode limits the clinical utility of the Simulix Evolution. With optimization, the system can be operated with clinically‐acceptable fluoroscopy images at exposures below 5 R/min. Cone‐beam CT image quality is currently compromised by the presence of ring artifacts and by poor HU uniformity and low‐contrast discrimination.