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A Gantry-Mounted Photon-Counting Detector Computed Tomography Prototype for Image Guided Proton Therapy.
Christian De Caro1, Yuting Lin2, Jufri Setianegara3
1Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin.
International Journal of Radiation Oncology, Biology, Physics
|February 20, 2026
Summary
Photon-counting detector (PCD) CT imaging was successfully integrated with a proton therapy gantry, demonstrating superior image quality over energy-integrating detectors (EIDs). This advancement enables more accurate electron density ratio estimation for adaptive proton therapy.
Area of Science:
- Medical Physics
- Radiological Imaging
- Radiation Oncology
Background:
- Current on-board kV imaging in proton therapy relies on energy-integrating detectors (EIDs), which have limitations in image quality and quantification accuracy.
- These limitations hinder the progress of online adaptive proton therapy and other advanced imaging applications.
- Photon-counting detectors (PCDs) offer potential improvements in image quality and spectral information.
Purpose of the Study:
- To experimentally demonstrate the feasibility of on-board photon-counting detector (PCD) CT imaging integrated with a proton therapy gantry.
- To evaluate the non-spectral image quality of PCD-CT compared to conventional EID-CBCT.
- To assess the spectral imaging capability of PCD-CT for electron density ratio estimation.
Main Methods:
- A CdTe-based PCD with 100 μm pixel size and two energy channels was mounted on an IBA Proteus ONE proton therapy system.
- PCD-CT scans were performed using the same acquisition protocol as clinical EID-CBCT for head imaging.
- Image quality was assessed using modulation transfer function (MTF) and contrast-to-noise ratio (CNR) with standardized phantoms; electron density ratios were estimated from spectral data.
Main Results:
- PCD demonstrated significantly higher detective quantum efficiency than EID, particularly at high spatial frequencies.
- PCD-CT achieved consistently higher CNR compared to EID-CBCT across various material inserts.
- Spectral PCD-CT data yielded a mean absolute percent error of 1.8% for estimated electron density ratios.
Conclusions:
- Gantry-mounted PCD tomographic imaging for proton therapy has been successfully demonstrated for the first time.
- The PCD-CT prototype offers superior non-spectral image quality compared to conventional EID-CBCT.
- The spectral imaging capability of PCD-CT enables accurate electron density ratio estimation, crucial for adaptive proton therapy.
