title: Development of a room laser based real-time alignment monitoring system using an array of photodiodes.
abstract: OBJECTIVE
  To develop a real-time alignment monitoring system (RAMS) to compensate for the limitations of the conventional room-laser-based alignment system. To verify the feasibility of the RAMS, reproducibility and accuracy tests were conducted.
  
  
  METHODS
  RAMS was composed of a room laser sensing array (RLSA), an electric circuit, an analog-to-digital converter (ADC), and a control PC. The RLSA was designed to arrange photodiodes in a pattern that results in the RAMS having a resolution of 1mm. The photodiodes were used for quantitative assessment of the alignment condition. To verify the usability of the developed system, we conducted tests of temporal reproducibility, repeatability, and accuracy.
  
  
  RESULTS
  The results of the temporal reproducibility test suggested that the signal of the RAMS was stable with respect to time. Further, the repeatability test resulted in a maximum coefficient of variance of 1.14%, suggesting that the signal of the RAMS was stable over repeated set-ups. The accuracy test confirmed that the "on" and "off" signals could be distinguished by signal intensity, considering that the "off" signal was below 75% of the "on" signal in every case. In addition, we confirmed that the system can detect 1mm of movement by monitoring the pattern of the "on" and "off" signals.
  
  
  CONCLUSIONS
  We developed a room laser based alignment monitoring system. The feasibility test verified that the system is capable of quantitative alignment monitoring in real time. We expect that the RAMS can propose the potential of the room laser based alignment monitoring method.
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Yu-Yun
authors.initials: YY
authors.lastname: Noh
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Tae-Ho
authors.initials: TH
authors.lastname: Kim
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Seong-Hee
authors.initials: SH
authors.lastname: Kang
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Dong-Su
authors.initials: DS
authors.lastname: Kim
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Min-Seok
authors.initials: MS
authors.lastname: Cho
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Kyeong-Hyeon
authors.initials: KH
authors.lastname: Kim
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Dong-Seok
authors.initials: DS
authors.lastname: Shin
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Do-Kun
authors.initials: DK
authors.lastname: Yoon
authors.affiliation: Department of Radiation Oncology, Virginia Commonwealth University, VA, USA.
authors.forename: Siyong
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea. Electronic address: suhsanta@catholic.ac.kr.
authors.forename: Tae Suk
authors.initials: TS
authors.lastname: Suh
mesh_terms: D055592:Biophysical Phenomena; D004867:Equipment Design; D005240:Feasibility Studies; D006801:Humans; D007834:Lasers; D008991:Monitoring, Physiologic / Q000295:instrumentation* / Q000706:statistics & numerical data; D056888:Patient Positioning / Q000295:instrumentation* / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D012985:Software Design
keywords: Patient alignment; Radiotherapy; Real-time monitoring; Room laser system