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In proton-based radiotherapy, proton radiography could allow for direct measurement of the water-equivalent path length (WEPL) in tissue, which can then be used to determine relative stopping power (RSP). Additionally, proton radiographs allow for imaging in the beam's-eye-view. In this work, a proton radiography technique using a flat-panel imager and a pencil-beam scanning (PBS) system is demonstrated in phantom. Proton PBS plans were delivered on a Varian ProBeam system to a flat-panel imager. Each proton plan consisted of energy layers separated by 4.8 MeV, and a field size of 25 cm × 25 cm. All measured data is binned into a layer-by-layer delivery in post processing. To build a calibration curve correlating detector response to WEPL, the plans were delivered to slabs of solid water of increasing thickness. Pixel-by-pixel detector response in the time/energy domain is then fit as a function of WEPL. Tissue equivalent phantoms are imaged for evaluation of WEPL accuracy. A spatial resolution phantom and a head phantom are also imaged. For all experiments, the detector was run with an effective pixel size of 0.4 mm × 0.4 mm. The proposed method reconstructed RSP with mean errors of 2.65%, -0.14%, and 0.61% for lung, soft tissue, and bone, respectively. In a 40 mm thick spatial resolution phantom, a 2 mm deep pinhole with 1 mm diameter can be seen. The accuracy and spatial resolution of the method show that it could be implemented for patient position verification. Further development could lead to patient-specific verification of RSP to be used for treatment guidance.

Cargo containers constitute the most critical component of global trade: 108 million containers represent the movement of about 95% of the world's manufactured goods. The steady increase in cargo container shipments has had a profound effect on world security: the threat associated with smuggling of shielded special nuclear material is elevated every year. Containers reaching the borders of the U.S. are currently not radiographically inspected due to time and dose considerations stemming from the use of bremsstrahlung beams for imaging. Bremsstrahlung spectra are low-energy peaked, resulting in low penetration values, especially through dense cargoes. The use of monoenergetic radiography beams could alleviate many of these problems due to higher energy and low background continuum. Using Monte Carlo simulations of a realistic imaging scenario with support from previous experimental measurements, we demonstrate how the use of monoenergetic photon beams in radiography can simultaneously reduce the radiation dose imparted to the cargo and any potential stowaways while increasing image quality. Dual-energy methods are leveraged to calculate material atomic number. Image quality is evaluated by measuring the noise standard deviation, contrast-to-noise ratio, and the pixel error as the dose is decreased., Competing Interests: The authors have declared that no competing interests exist.

The technique of spectral radiography has been shown to accurately discriminate a material’s elemental composition by using known X-ray physics. In previous work, we presented a system for determining the total compositional mass of UO2 powder. This is achieved with a state-of-the-art pixelated spectrometer and a high-fidelity physical model. Similar to other radiographs, the system suffers from partial-volume attenuation where the sample projection onto a pixel is only a fraction of the pixel area, leaving the rest unattenuated. This study updates the physical model to account for fractional area which challenges the existing algorithm. We present how this update is made and explore approaches to stabilize the algorithm through parameter scaling, constrained optimization, and hyperparameter selection. We applied the updated algorithm to calculate the total uranium and oxygen mass of UO2 powder simulations. The average relative error on total uranium mass was reduced from 1.4% to 0.068% and on total oxygen mass from 122.2% to 4.2%. [ABSTRACT FROM AUTHOR]