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Use of An Easily-Modified Simple Phantom to Perform the Daily and Monthly Localization QA Tasks for a Video-Based Surface Imaging System

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C Kim

C Kim*, E Furhang , C Devick , Mount Sinai Beth Israel, New York, NY


SU-G-JeP3-11 (Sunday, July 31, 2016) 5:00 PM - 5:30 PM Room: ePoster Theater

Purpose: To describe a simple, easily fabricated, Styrofoam phantom used in conjunction with a commonly available OBI phantom, to QA a video-surface imaging system according to TG147, using minimal effort.

Methods: Styrofoam, a common packaging material, reflects the speckled AlignRT light very well. A Styrofoam block was used as a partial cap to attach onto a standard Varian Marker Match phantom. The cap was engraved with two sets crosshairs on each surface, one at the ‘zero’(center) and the other an ‘off-centered’ position, 2 cm in all three orthogonal directions. A reference image is obtained at ‘zero’ position. For the daily test, static localization check is performed by aligning the phantom with room lasers at ‘off-centered’ position and then the couch is shifted to match the ‘zero’ with the lasers. For the monthly test, plate calibration is recommended to define a relationship between an image point on the camera and that of the isocenter in the treatment room. Static localization accuracy is checked using a hidden-target test, which is an extension of daily static localization procedure. The phantom positioned at ‘off-centered’ is shifted to make the readings 0.0 cm for all orientations. The location of the hidden target is then verified by taking orthogonal kV images or CBCT.

Results: The AlignRT tests required by TG147 are quite similar to those performed on on-board imaging (OBI). Overall alignment of the system is maintained with RMS < 1 mm and any potential problems were identified. The system’s static location is maintained within ± 1 mm. The same accuracy can be obtained for a monthly hidden target test which is integrated with an OBI QA.

Conclusion: A customized phantom is tested and a routine QA program for surface-imaging system is introduced. By dealing with a single phantom, the procedure can achieve similar goals efficiently.

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