SU‐G‐JeP3‐11: Use of an Easily‐Modified Simple Phantom to Perform the Daily and Monthly Localization QA Tasks for a Video‐Based Surface Imaging System

Abstract

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.