Room: Exhibit Hall | Forum 5
Purpose: An emerging technology, Intrafraction Imaging, which allows for KV cone beam CT (CBCT) acquisition simultaneous to VMAT delivery, has been investigated. In this study, simultaneous CBCT imaging with MV on the Elekta Synergy is investigated using phantoms for image quality analysis. The aims of the study include demonstration of intrafraction imaging that can be integrated functionally into the clinical workflow, and evaluation of image degradation due to scattered photons from the orthogonally directed treatment beam.
Methods: CBCT acquisition was performed with and without MV VMAT for image comparison. The MV deliveries included (1) a high-dose typical lung VMAT SBRT (10 Gy/arc) and (2) a low-dose esophagus VMAT (1.5 Gy/arc) plan on an anthropomorphic chest phantom. The same fields were delivered to a geometric phantom (CatPhan600) for further image quality analysis including noise power spectrum, MTF, and CNR and HU linearity.
Results: The integrated functionality and quality of simultaneous kV CBCTs was entirely sufficient to perform a successful image registration for post-treatment position verification. The ability to resolve line-pairs was found to be unaffected by the MV beam. Hounsfield were minimally affected in the MV + KV CBCT, however a low contrast visibility test was significantly degraded (5%) with MV on versus no MV (0.8%). Further studies were performed to analyze the MV scatter correction that works by acquiring images on the XVI panel when the kV beam is OFF, subtracted out from the kV ON images which then go into reconstruction.
Conclusion: Intrafraction imaging with simultaneous MV treatment and kV CBCT imaging has potential to verify patient position and assess if off-line adaptive re-planning is necessary. Additionally the simultaneous CBCT acquisition during treatment may potentiate internal motion tracking of targets and organs at risk, and unlock further potential for adaptive radiotherapy.
Funding Support, Disclosures, and Conflict of Interest: The Intrafraction Imaging software was provided to UC Davis by Elekta in accordance with a research agreement.