Room: ePoster Forums
Purpose: An end-to-end Winston Lutz test measures the cumulative targeting error of the entire treatment planning and delivery chain for a stereotactic radiotherapy system. CT imaging is a central part of external beam treatment planning, and C-arm linear accelerator treatment devices employ Cone Beam CT image guidance systems. Metal components can generate significant image artifacts in CT and CBCT images and can undermine their use test phantoms for that undergo CT and CBCT imaging. In this work we investigate the use of a non-metallic sphere as the target in a CT-compatible End-to-End Winston-Lutz phantom.
Methods: An anthropomorphic head phantom was used to build the End-to-End Winston-Lutz test device. The head phantom has a rectangular cavity measuring 64mm by 64mm by 95 mm. A Styrofoam block was shaped to the dimensions of the cavity. A Polytetrafluoroethylene (PTFE, commonly known by the trade name Teflon), sphere of diameter 12.5 mm was embedded in the center of the Styrofoam block, which was then placed inside the head phantom. The phantom was then used to perform an End-to-End Winston-Lutz test. The test involved 8 beams at a range of gantry, collimator and couch angles, each with a square field of side 3 cm. The portal beam energy was 2.5MV.
Results: The PTFE sphere was clearly visible in each of the Winston Lutz portal images. For each image, the attenuation of the beam was measured at the center the sphere image. The average, mean, and maximum attenuation was 22.0%, 19.3%, and 24.7% respectively. The set of images were successfully analyzed with the DoseLab Winston-Lutz analysis program.
Conclusion: The attenuation offered by a non-metallic sphere can be adequate for use in a Winston-Lutz End-to-End test. Additional work will be required to refine the design and imaging parameters in such a test device.