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Commissioning and Acceptance Testing of Optical Surface Monitoring System On TrueBEAM STx as Per Task Group 147

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V Mhatre

V Mhatre*, P PATWE , P Dandekar , Sir HN RF Hospital, Mumbai, Maharashtra


SU-G-JeP4-4 (Sunday, July 31, 2016) 5:30 PM - 6:00 PM Room: ePoster Theater

Purpose :Optical Surface Monitoring system (OSMS) have been recently introduced by Varian for initial patient positioning and real-time monitoring during complex radiotherapy treatment.The purpose of this work was to implement TG 147 with OSMS.

Methods:Recently we installed OSMS first of its kind in India on trueBEAM STx at our Institue.The OSMS is composed of a three cameras ceiling mounted and a Workstation. The following tests were performed to validate the system a.Calibration b.System reproducibility and drift c.Static localization displacement accuracy and d.Dynamic radiation gating delivery.The Calibration procedure consists of Daily,Monthly and MV Radiation Isocenter Calibration.The reproducibility of system was tested by monitoring the varian gating phantom test pattern for at least 120 min.
Each recorded pattern was registered to the reference surface to calculate the required couch adjustment.To measure the static localization displacement accuracy of the system to detect and quantify patient shift relative to a reference image,we compared the shift detected by the surface imaging system with known couch transitions in a phantom study.The phantom was set in a motion and the radiation beam was holded by changing the threshold in the software for different clinical setups to test the dynamic radiation gating capability.

Results:Daily calibration was within ±0.5 mm.The MV radiation isocentre with respect to cameras was less than 1 mm in translational axis and less than 0.5° for rotational axis. The reproducibility was found to be 0.4 mm. The maximum static displacement accuracy was 0.75 mm for the three translational axis, and less than 0.5° for rotational axis. The system was able to hold the beam with a minimum threshold of 1 mm .

Conclusion :A quality assurance process has been developed as per TG 147 for the clinical implementation of an OSMS in radiation therapy.

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