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Development of a Room Laser Based Real-Time Alignment Monitoring System Using An Array of Photodiodes

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Y Noh

Y Noh1*, S Kim2 , T Kim1 , S Kang1 , D Kim1 , M Cho1 , K Kim1 , D Shin1 , T Suh1 , (1) Department of Biomedical Engineering and Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Korea, (2) Department of Radiation Oncology, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA


SU-F-J-44 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To develop a real-time alignment monitoring system (RAMS) to compensate for the limitations of the conventional room laser based alignment system, and to verify the feasibility of the RAMS.

Methods: The RAMS was composed of a room laser sensing array (RLSA), an analog-to-digital converter, and a control PC. In the RLSA, seven photodiodes (each in 1 mm width) are arranged in a pattern that the RAMS provides alignment in 1 mm resolution. It works based on detecting laser light aligned on one of photodiodes. When misaligned, the laser would match with different photodiode(s) giving signal at unexpected location. Thus, how much displaced can be determined. To verify the reproducibility of the system with respect to time as well as repeated set-ups, temporal reproducibility and repeatability test was conducted. The accuracy of the system was tested by obtaining detection signals with varying laser-match positions.

Results: The signal of the RAMS was found to be stable with respect to time. 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. In the accuracy test, signals between when the laser was aligned and not-aligned with any of sensors could be distinguished by signal intensity. The signals of not-aligned sensors were always below 75% of the signal of the aligned sensor. It was confirmed that the system could detect 1 mm of movement by monitoring the pattern of signals, and could observe the movement of the system in real-time.

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. The system is relatively simple, not expensive, and considered to be easily incorporated into conventional room laser systems for real-time alignment monitoring.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by the Mid-career Researcher Program through NRF funded by the Ministry of Science, ICT & Future Planning of Korea (NRF-2014R1A2A1A10050270) and by the Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (No. 2013M2A2A7038291)

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