Purpose: In this work, we demonstrate the system design and preliminary images obtained using our novel integrating proton radiography system consisting of a monolithic volume of plastic scintillator and an optical camera.
Methods: The system consists of a monolithic plastic scintillator volume (20 x 20 x 20 cm³) capable of capturing a wide range of proton beam energy depositions. The scintillator captures the slowed and scattered proton beam after it exits from the phantom, producing a scintillation light distribution. A charge-coupled device (CCD) placed along the beam’s-eye-view direction captures an integral of the scintillation light along the beam axis to generate the radiograph. The imaging system was tested for uniformity, stability, linearity, and accuracy in measuring water-equivalent thickness (WET). A custom spatial and contrast resolution phantom was radiographed for qualitative assessment.
Results: A coefficient of variation (CV) was calculated over 10 radiographs collected by the system and the resulting system stability was determined to be 0.37%. The system’s ability to image the dose uniformly over a radiograph was evaluated by calculating the CV over a 5 x 5 cm area and was found to be 2.6%. The system response was found to be highly linear (R² = 1) over a range of two orders of magnitude in deposited dose (1 – 92 mGy). The WET was calculated for a Gammex solid water phantom insert with a relative accuracy of 0.25%. To improve contrast for the resolution phantom, radiograph image thresholding was applied by rejecting low pixel intensities (< 30% of the peak pixel intensity in the image).
Conclusion: The preliminary images and studies conducted on the monolithic scintillator system design demonstrate its excellent linearity, uniformity, stability, and WET calculation accuracy. Our system therefore has the potential to be adopted clinically for proton radiography.