Author: Anahita Bakhtiari Moghaddam, Don F. DeJongh, Ethan DeJongh, Jennifer Hardt, Oliver Jäkel, Lukas Martin, Alexander Pryanichnikov, Joao Seco, Christina Stengl, Niklas Wahl 👨🔬
Affiliation: Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Division of Biomedical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), ProtonVDA LLC, Department of Physics and Astronomy, Heidelberg University, Division of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT) 🌍
Purpose:
To evaluate the feasibility and performance of single-plane position tracking for proton and helium pencil beam radiography using a prototype imaging system, with the goal of providing a cost-effective solution for proton radiography and enabling helium radiography in mixed carbon-helium beams.
Methods:
The study used the low-intensity extraction mode of the Heidelberg Ion Beam Therapy (HIT) synchrotron to generate proton and helium beams for imaging. A customized ProtonVDA scanner served as the particle detector. Various phantoms were employed, including 3D printed spatial resolution phantoms, motion phantoms to evaluate motion tracking, and cylindrical PMMA phantoms with tissue equivalent inserts to evaluate water equivalent thickness (WET) accuracy. Anthropomorphic abdominal and lung phantoms were also used to simulate realistic clinical conditions. Imaging parameters such as spatial resolution, frame rate and WET accuracy were quantified.
Results:
Single-event radiography protocols were established. Spatial resolution reached 1 lp/mm for helium and 0.5 lp/mm for proton beams in single-plane configurations for the simple line phantoms Motion phantom imaging was achieved at a frame rate of 2 fps over a field size of 10 cm × 10 cm. WET reconstruction accuracy was measured to be less than 2 mm for protons and 3 mm for helium ions over eight tissue-equivalent slices. Results from anthropomorphic phantoms demonstrated the potential of the method for application to complex geometries.
Conclusion:
This phantom study confirms the feasibility of single plane position tracking for proton and helium pencil beam radiographs. The system demonstrated acceptable spatial resolution and WET reconstruction accuracy. Future efforts will focus on improving image quality for complex geometries, reducing noise for helium imaging, and developing real-time radiographic reconstruction capabilities during beam pauses.