Equivalence of Single-Energy 120kVp and Dual-Energy 120kVp-like Virtual Monochromatic CT Images In Treatment Planning Applications
Abstract
Purpose
To establish the equivalence of dual-energy 120kVp-like virtual monochromatic images (VMIs) to 120kVp standard single-energy CT images in terms of electron density, image quality, and as applied to clinically representative external beam therapy plans.
Methods
All Images were acquired on a GE RevolutionTM Apex CT scanner. Three sets of scans were acquired for each comparison made: 1) a single energy at 120kVp and 300mA, 2) a dose-matched (DM) dual energy 120kVp-like with tube current set to produce equivalent CTDIvol, and 3) a noise-matched (NM) 120kVp-like with tube current set to produce equivalent standard deviation sampled across the scan. Hounsfield units were assessed with the Sun Nuclear Advanced Electron Density phantom. Image quality was evaluated with Sun Nuclear IQphanTM and RapidCHECKTM. Scans of the Alderson RANDO phantom and Tecnosan MAX-HDTM phantom were used to create clinically representative VMAT plans for brain, lung, and prostate in Varian EclipseTM. The same plan was applied to each scan type and region and compared via plan subtraction and DVH metrics.
Results
Electron density curves derived from DM and NM, produced relative electron densities within 2.7% and 2.6%, respectively, of those from 120kVp. All scans produced similar image quality in terms of geometric distortion (0.4-0.5 mm) and high contrast resolution (6.5-6.8 lp/mm). Low contrast detection was the same for 120kVp and NM, and slightly better for DM images. Plans produced nearly identical DVHs, and plan subtractions showed minimal deviations between 120kVp and VMIs.
Conclusion
This work confirms that plans made with the 120kVp-like VMI reconstructions produced by the GE Revolution Apex CT scanner are clinically equivalent to those from standard single energy scans. Thus, future applications of dual energy CT in the clinic may be used without compromising plan quality or requiring redundant scans.