ESTRO 2021 Abstract Book

S1390

ESTRO 2021

PO-1667 Statistical limitations in particle imaging tomography C. Fekete 1 , N. Dikaios 2 , E. Baer 1 , P.M. Evans 2 1 University College London, Medical Physics and Biomedical Engineering, London, United Kingdom; 2 University of Surrey, Centre for Vision, Speech and Signal Processing, Surrey, United Kingdom Purpose or Objective To investigate the capacity of various ion beams available for radiotherapy to produce high quality relative stopping power (RSP) maps acquired from energy-loss measurements and to establish a model relating signal- to-noise ratio (SNR) and spatial resolution with particle energy and object size and the various image- formation electromagnetic processes. Materials and Methods Tomographic RSP map’s SNR and spatial resolution are compared between various ions as a function of dose and energy loss. SNR and spatial resolution are calculated from first principles but require measurements of energy deposited and nuclear attenuation in the middle of the phantom. These parameters are acquired from Monte Carlo simulations (n=10 7 histories/simulation) of: proton, helium, lithium, boron and carbon ion beams crossing a 10(15) cm radius water phantom, with initial energy varying between 110 and 300 MeV in steps of 10 MeV. Results For a fixed ion, the SNR is found to decrease with thickness crossed and, independently, increase with decreasing energy (see Figure 1). The scattering noise is dominant around high-gradient edge whereas the straggling noise is maximal in homogeneous regions. Image quality metrics are found to behave oppositely against energy: lower energy minimizes both the noise and the spatial resolution, with the optimal energy choice depending on the application and location in the imaged object. For a fixed energy and varying ion (see Figure 2), it was found that protons possess a significantly larger SNR when compared with other ions at a fixed range (up to 36% higher than helium) due to the proton nuclear stability and low dose per primary. However, it also yields the lowest spatial resolution against all other ions, with a resolution lowered by a factor 4 compared to that of carbon imaging, for a beam with the same initial range. When imposing an energy that provides a clinically relevant fixed spatial resolution (10 lp/cm), carbon ions produce the highest image quality metrics with proton ions producing the lowest.