Author: Liu Hong, Zhong Su 👨🔬
Affiliation: University of Arkansas for Medical Sciences, Department of Radiation Oncology, University of Arkansas for Medical Sciences (UAMS) 🌍
Purpose: During treatment delivery on TrueBeam platform 2.7, Triggered Imaging (TI) enables kV images acquisition at regular intervals and Auto Beam Hold (ABH) provides beam pausing if the target is moving outside the tolerated region. Clinical investigation of TI and ABH with the spherical fiducials and further determination of the kV acquisition parameters and image settings are performed and presented.
Methods: The Dynamic Thorax Phantom and SBRT Rod insert with embedded spherical target and three radiographically visible fiducials have been imaged and treated using TI and ABH during VMAT treatment. CBCT was acquired for phantom positioning and alignment. The fiducials were contoured on planning CT and used to guide the image matching as Markers with a Searching Region having 5mm expansion of the fiducial contours. The beam was held by ABH if less than two fiducials detected or within tolerance in the image. ABH using kV Imaging triggered by elapsed time, MU and gantry rotation were evaluated with ABH for efficacy and safety of intra-fraction treatment delivery with target motion in all three directions.
Results: TI based on Time and MU enabled the effective and safe control of beam irradiation over the treatment delivery process. Gantry rotation trigger was unreliable as the rotation might get stuck at arbitrary angle once less than two fiducials detected or within tolerance, which led ABH holding the beam indefinitely. Delay ABH and Overlay Structures (target/fiducials) were recommended being enabled to delay beam pausing (pause-only if fiducials are not detected in two sequential images) and allow visual inspection by operator, as poor fiducial detection may occur occasionally due to overlying structure or overlapping fiducials.
Conclusion: ABH using TI is clinically feasible and has potential to improve dose delivery on moving target. Further dosimetry verification in phantom and clinical investigation in selective patient group are required.