SU‐FF‐I‐86: Commissioning and Evaluation of An Amorphous Silicon Flat‐Panel Digital Imaging System (XRD 1640, Perkin Elmer) for Its Application in Proton Beam Therapy

Abstract

Purpose: Accurate, patient‐specific anatomical information is a prerequisite for successful radiation therapy planning and delivery to the tumor, while minimizing dose to surrounding tissues. A new FPDI system (XRD 1640, Perkin Elmer) was installed and commissioned replacing a CCD and mirror‐based digital imager (DI, Optivus). The details of the tests performed during the commissioning will be presented. Methods and Materials: Rando phantom is used for testing patient orientation in the imager. A RMI magnification plate and a radio‐opaque ruler are used to measure the magnification factor of the imaging system. A black‐hole phantom along with a line‐pair phantom, aluminum and copper plates are used to measure the image quality. To test the alignment of two sources (x‐ray and proton), the x‐rays and proton beam double‐exposure (one x‐ray and one proton) was done on two cross‐wires (one in the aperture and one in front of FPDI) at four cardinal angles. To test the drift of the nozzle, the same test (with two double‐exposures) was done for nozzle at fully extended and fully retracted positions and at different gantry angles. Results: FPDI requires low x‐ray energy settings (90 kVp, 20–40 mAs) for collecting images of similar quality when compared to the previous imager (105 kVp, 250 mAs). The acceptance test showed the maximum high‐contrast spatial visibility (resolution) of 0.8 line pairs per mm and the maximum low‐contrast visibility (resolution) of 0.5 mm diameter circular objects. The images obtained from double‐exposure as well as two double‐exposures showed the coincidence within 1 mm. The FPDI images obtained from Rando phantom depicted differences to the images of exported DRRs, which enabled the correct adjustment of the phantom alignment and orientation. Conclusion: When compared to the previous imager, FPDI provides a sharper image for locating the landmarks for patient alignment with less exposure to the patient. © 2006, American Association of Physicists in Medicine. All rights reserved.