Author: Jared Baggett, Wesley E. Bolch, Lukas M. Carter, Laura Dinwiddie, Benjamin Taylor Heggie, Adam Leon Kesner, Juan Camilo Ocampo Ramos, Graham Joseph Stoddard 👨🔬
Affiliation: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, University of Florida, MD Anderson 🌍
Purpose: The objective of this study is to develop a physical phantom to quantify tube current modulation (TCM) and assess the limitations of a TCM model used in Monte Carlo patient CT organ dose estimations. The existing TCM method applies a generic attenuation correction factor, thus by empirically determining more realistic adjustment factors for specific TCM schemes we aim to make the Monte Carlo organ dose estimations derived from the CT source model more representative of examinations performed under commercially available TCM schemes.
Methods: A physical phantom was designed using a stepped arrangement of ellipsoidal segments and constructed from high-density polyethylene (HDPE). Six elliptical sections, with increasing lateral dimensions of 15, 20, 25, 30, 35, and 40 cm, were chosen following the anteroposterior (AP) and lateral dimensions reported by AAPM Report 220 based on water-equivalent diameter to represent varying patient anatomies. The outer body of the phantom and its stand were constructed using precision machine milling. Rod-shaped holders for optically stimulated luminescent dosimeters (OSLDs) were 3D printed and embedded in the phantom to collect dosimetric measurements under both static and modulating tube currents in a Canon Aquilion ONE Genesis CT scanner. Preliminary dosimetric measurements were performed using the OSLDs and the phantom under static tube current and a comparable virtual scan was simulated on a digital model of the phantom in PHITS.
Results: The phantom was successfully designed and constructed. Preliminary scan results showed agreement between the physical and virtual scans within 5% under static tube current.
Conclusion: The developed phantom represents a promising tool for evaluating tube current modulation in CT imaging.