Evaluation of the impact of a scanner prototype on proton CT and helium CT image quality and dose efficiency with Monte Carlo simulation

Speaker: Stefanie Götz
Institution: Ludwig-Maximilians-Universität München, Germany

Abstract

There is great interest in the use of ion CT for image acquisition in modern particle therapy treatment planning since it promises to yield improved relative stopping power (RSP) maps compared to conventional x-ray CT as required for the planning procedure. This study investigates image quality in proton (pCT) and helium CT (HeCT) focusing on image noise, spatial resolution, dose efficiency and RSP mean absolute percent error (MAPE) using the detailed Geant4 implementation of the phase-II pCT scanner prototype [1,2,3].

pCT and HeCT image acquisition scans of four phantoms are simulated allowing the evaluation of noise (expressed as image variance), spatial resolution, dose and RSP accuracy. The imaging dose required to achieve the same image noise in a water and a head phantom is estimated at both native spatial resolution and in a scenario where the HeCT spatial resolution is reduced and matched to that of pCT using Hann windowing of the reconstruction filter.

The scanner prototype is expected to yield a higher spatial resolution for HeCT than pCT by a factor of 1.8 (0.86lp/mm vs. 0.48lp/mm at the centre of a 200mm water phantom). At native spatial resolution, HeCT requires a factor of 2.9 more dose than pCT to achieve the same noise while at matched spatial resolution, HeCT requires only 38% of the pCT dose. Finally, the RSP MAPE is 0.59% for pCT and 0.67% for HeCT.

The spatial resolution advantage of HeCT comes at the cost of increased dose. Matching spatial resolution via Hann windowing demonstrates that HeCT has a substantial dose advantage. Both modalities provide state-of-the-art RSP MAPE.

[1] V.A. Bashkirov et al. (2016), Med. Phys. 43, 664-674, doi: 10.1118/1.4939255.
[2] R.P. Johnson et al. (2016), IEEE Trans. Nucl. Sci. 63, 52-60, doi: 10.1109/TNS.2015.2491918.
[3] V. Giacometti et al. (2017), Med. Phys. 44, 1002-1016, doi: 10.1002/mp.12107.

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