Implementation of a parallel-beam optical-CT apparatus for three-dimensional radiation dosimetry using a high-resolution CCD camera Wen-Tzeng Huang a , Chin-Hsing Chen b , Chao-Nan Hung c , Chiu-Ching Tuan c , Yuan-Jen Chang b,d,n a Department of Computer Science and Information Engineering, Minghsin University of Science and Technology, Taiwan, ROC b Department of Management Information Systems, Central Taiwan University of Science and Technology, Taichung, Taiwan, ROC c Graduate Institute of Computer and Communication Engineering, National Taipei University of Technology, Taiwan, ROC d Institute of Biomedical Engineering and Materials Science, Central Taiwan University of Science and Technology, Taichung, Taiwan, ROC article info Available online 21 January 2015 Keywords: CCD Optical CT Gel dosimeter NIPAM gel SNR MTF abstract In this study, a charge-coupled device (CCD) camera with 2-megapixel (1920  1080-pixel) and 12-bit resolution was developed for optical computed tomography(optical CT). The signal-to-noise ratio (SNR) of our system was 30.12 dB, better than that of commercially available CCD cameras (25.31 dB). The 50% modulation transfer function (MTF50) of our 1920  1080-pixel camera gave a line width per picture height (LW/PH) of 745, which is 73% of the diffraction-limited resolution. Compared with a commercially available 1-megapixel CCD camera (1296  966-pixel) with a LW/PH¼358 and 46.6% of the diffraction- limited resolution, our camera system provided higher spatial resolution and better image quality. The NIPAM gel dosimeter was used to evaluate the optical CT with a 2-megapixel CCD. A clinical five-field irradiation treatment plan was generated using the Eclipse planning system (Varian Corp., Palo Alto, CA, USA). The gel phantom was irradiated using a 6-MV Varian Clinac IX linear accelerator (Varian). The measured NIPAM gel dose distributions and the calculated dose distributions, generated by the treatment planning software (TPS), were compared using the 3% dose-difference and 3 mm distance-to-agreement criteria. The gamma pass rate was as high as 98.2% when 2-megapixel CCD camera was used in optical CT. However, the gamma pass rate was only 96.0% when a commercially available 1-megapixel CCD camera was used. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Gel dosimetry has attracted much attention for its potential to achieve validation of three-dimensional (3D) dose distributions, compared with ‘traditional’ dosimeters [1]. However, the accuracy, precision, and an economic readout tool for gel dosimetry are still challenges for general application in the clinic [2]. Some imaging modalities, such as magnetic resonance imaging (MRI), optical CT, X-ray CT, and ultrasound have been assessed as measurement tools for gel dosimeters. Considering the latest developments in gels, such as polymer gels and radiochromic gels [3], optical CT has great potential and is worthy of more detailed investigation. Several optical CT scanning systems have been developed [4–9]. The first-generation laser- based optical CT ‘OCTOPUS’ scanner, developed by MGS (MGS Research, Inc., Madison, CT, USA), has long been considered the ‘gold standard’ due to its reliable and precise results, compared with treatment plan systems (TPSs) [7]. A CCD-based optical CT scanner can acquire a complete plane of data at each step, and obtain a complete 3D dose distribution rapidly, typically with a speed increase of at least an order of magnitude, compared with a laser-based optical CT system [6]. Additionally, inexpensive and high-resolution CCD-based optical CT may be achievable if CCD cameras can be developed with improved signal quality and reduced cost [2]. In this study, a complete parallel-beam optical CT scanning system was developed, including an imaging system, optical lens, image sensor, and image-processing system. Additionally, we propose a variety of CCD signal-processing algorithms to reduce noise, such as pixel response non-uniformity and the use of a bias clamp. The results were evaluated by comparing the system with commercially available CCD and CMOS cameras. In the design of a low-noise camera system, not only the analog front-end (AFE) design [14] but also analysis of the CCD signal needs to be discussed. The CCD output signal will be changed with varying incident light. However, in the absence of a CCD image Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A http://dx.doi.org/10.1016/j.nima.2015.01.050 0168-9002/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: ronchang@ctust.edu.tw (Y.-J. Chang). Nuclear Instruments and Methods in Physics Research A 784 (2015) 590–596