Program Information
Monte Carlo Simulation of Contrast-Agent Induced Local Dose Build-Up in An Anthropomorphic Abdomen Phantom: Effects of Different CT X-Ray Spectra On Relative Absorption Increase
A Steuwe*, H Kauczor , W Stiller , University Hospital Heidelberg, Heidelberg, Germany
Presentations
TU-RPM-GePD-IT-2 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Imaging ePoster Theater
Purpose: To assess the contrast-agent induced local dose build-up and relative absorption increase for different CT X-ray spectra in an anthropomorphic abdomen phantom using Monte Carlo simulations.
Methods: The influence of different X-ray spectra (measured in-house at 120kVp, and spectra generated using an online tool for the simulation of X-ray spectra at 100kVp and 120kVp with 3.3mm aluminum filtration) on the contrast-agent induced local dose build-up and relative absorption increase in an anthropomorphic abdomen phantom was determined using Monte Carlo simulations with Geant4. Organs were divided into two parts: a core and a surrounding shell of 2.5mm thickness. Energy deposition in organ subvolumes and surrounding soft tissue (ST) shells of 2.5mm thickness were individually tracked. Relative absorption increase for same tissues (core, organ- and ST-shells, surr. tissues) and between neighboring shells (energy deposition normalized to volume) were studied in absence and presence of iodine (concentration ~ 5mg/ml) in the pancreas, spleen, kidney, and liver.
Results: In presence of iodine, energy deposition increases for the specified organs, but decreases (ΔE_{rel,surr.tissues}=~2%)in all surrounding tissues. Relative energy increase is larger for organ shells than for the inner cores (ΔE_{rel,core}=[26.8%, 45.9%], ΔE_{rel,organ-shells}=[34.4%, 46.5%]). The lowest ΔE_{rel} is found in the liver, the highest ΔE_{rel} in the pancreas. Absorption decreases for soft tissue shells (ΔE_{rel,ST-shell}=[-5.0%, -1.9%]), especially in regions towards the phantom center. In absence of iodine, ΔE_{rel,interface} ranges between 2.5% and 25.2%. In presence of iodine, ΔE_{rel,interface} increases to 54.8% to 77.1%, with the lowest ΔE_{rel,interface} for the pancreas, and highest ΔE{rel,interface} for the liver.
Conclusion: Differences in ΔE_{rel} and ΔE_{rel,interface} between tube potentials are small. In presence of iodine, energy deposition especially increases at the organ shells, showing a local contrast-agent induced dose build-up, whereas in turn energy deposition decreases in the soft tissue surrounding the organs.
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