TITLE:
Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator
AUTHORS:
Junfang Gao, Xiaoqian Liu
KEYWORDS:
Winston-Lutz-Gao Test, off-Iso Winston-Lutz Test, Single Iso-Multiple Mets’ Treatment
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.8 No.1,
January
21,
2019
ABSTRACT: In the
linear accelerator-based
stereotactic radio surgery
(SRS) and stereotactic body radiotherapy (SBRT) programs, single isocenter-multiple metastases’ treatment has become more and more popular due to
their high
efficiency in treatment time. However, the absence of a comprehensive quality
assurance program is still the challenge for medical physicists. The Winston-Lutz-Gao test, which
we developed two years ago, was performed
for the first time on a True Beam STx (Varian Medical System) linear accelerator in this study. Beams were designed by Eclipse with gantry,
collimator, and couch full rotations, and a 200-pound weight was placed on the couch to mimic real treatment. The “frameless SRS QA target pointer” from the Brainlab
company, with a 3.5-mm
metallic ball embedded in the center, was used as a phantom. Images were acquired by the
portal imager built-in
linear accelerator and analyzed directly by the Image browser in ARIA. We found
that the farther the metastases were from the linac isocenter, the worse the congruence was between the
beam mechanical and the radiation center. The farthest metastases should be within 6 cm from the linac isocenter per the AAPM TG-142 and American Society for Radiation Oncology (ASTRO)
white paper criteria. To the best of our knowledge, this is the first
off-isocenter Winston-Lutz test performed on a True Beam STx linear accelerator.