ESTRO 2022 - Abstract Book

S170

Abstract book

ESTRO 2022

Figure 2: Heatmap of uncertainty vs edit for (a) heart and (b) esophagus.

MO-0214 Integral proton radiography scatter reduction through pencil beam pixel weighting and thresholding

D. Robertson 1 , C. Darne 2 , C. Fekete 3 , S. Beddar 2

1 Mayo Clinic, Radiation Oncology, Phoenix, USA; 2 The University of Texas MD Anderson Cancer Center, Radiation Oncology, Houston, USA; 3 University College London, Medical Physics and Biomedical Engineering, London, United Kingdom Purpose or Objective The purpose of this study is to develop a new integral proton imaging approach using beam-by-beam processing with pixel weighting and thresholding (PWT) for proton scatter reduction. Proton radiography can improve image guidance, decrease stopping power uncertainty, and streamline adaptive radiotherapy workflows. Most proton radiography research focuses on single proton tracking detectors, but technical challenges including high count rates and the expense and complexity of detector assemblies have slowed clinical adoption of these systems. Integrating detectors employing scintillators and cameras circumvent these challenges, but proton scattering increases image noise and decreases contrast and water-equivalent thickness (WET) accuracy. The PWT imaging approach can improve image quality while maintaining the benefits of integrating proton imaging. Materials and Methods The detector comprises a cubic block of plastic scintillator with 20 cm side length and a camera facing the beam nozzle (Fig. 1a). A collection of calibration curves is formed by imaging a single pencil beam as a function of penetration depth in the scintillator and distance from the beam center (Fig. 1b-c). An object is imaged by interposing it between the nozzle and the scintillator and scanning a proton pencil beam across the object. The camera acquires one image per proton pencil beam. The intensity of each camera pixel is converted to a proton WET via the calibration curves (Fig. 1d). Several proton beams may contribute to a single pixel. The WET for each pixel is determined by weighting all pixel contributions by the fraction of the peak intensity of the reference pencil beam. Proton scattering is decreased through this weighting process and by rejecting pixel contributions whose baseline intensity is below 50% of the peak intensity of the reference pencil beam. A Monte Carlo simulation of the detector was implemented in Geant4, including an aluminum “Las Vegas” contrast-detail phantom with a WET of 47.7 mm. Proton radiographs were reconstructed via the PWT method, by integral proton radiography without spot-by-spot PWT processing, and also by a simulated single particle tracking detector comprising two tracking planes and an energy calorimeter.