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Feasibility of Using Octavius 4D Phantom in Dose Rate Versus Gantry Speed Test for RapidArc Commissioning

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B YANG*, H GENG , C Cheung , Y DING , C Kong , W Lam , K Cheung , S Yu , Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong


SU-I-GPD-T-448 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the feasibility of using Octavius 4D phantom in dose rate versus gantry speed test.

Methods: A specific plan was created with dose rate ranging from 36 MU/min to 600 MU/min and gantry speed varying from 3°/s to 6°/s, which was delivered using TrueBeam linear accelerator thereafter. Octavius 4D phantom is capable of reconstructing 3D dose using a single planar array that rotates in synchrony with the gantry and records the gantry angle continuously through an inclinometer. The phantom was isocentrically set up and set to measure data with a sampling rate of 10 Hz. Machine trajectory log files were also collected for comparison.

Results: The mean deviation of measured gantry angle from log data was less than 0.2° and the derived gantry speed was within 1.8% variation of the expected value. The mean deviation of measured dose rate was 0.05%, with range of -0.20% to 0.38%. The characteristic parameter MU/° was also calculated and its deviation ranged from -1.9% to 1.5%. The modulation of dose rate and gantry speed synchronized accurately with the time difference less than the temporal resolution of 100ms and the deviation of derived actual gantry angle at each control point was within 0.4°. The transit of modulation could also be tracked successfully.

Conclusion: Our proposed method using Octavius 4D phantom has been proved to be accurate and convenient in dose rate vs gantry speed test. Gantry speed, dose rate and their synchrony could be directly measured and compared with the plan settings.

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