Flat panel proton radiography in high-precision image-guided mouse brain proton irradiation

Further development of proton therapy takes place largely through in-vivo experiments, which are subject to increasingly strict ethical and technical requirements. Proton irradiation of small animal organs demand for highly suitable experimental setups and intelligent protocols to mimic clinical workflows as closely as possible. This includes the possibility of on-beam imaging for precise positioning and treatment. To meet these requirements, proton radiography was integrated into an existing beam setup for mouse brain proton irradiation at the University Proton Therapy Dresden (UPTD).
For the realization of the radiography a flat panel detector was installed on proton beam axis behind mouse position. Transmission imaging was achieved by increasing the proton energy significantly above that required for brain irradiation, i.e. the protons pass through the mouse and reach the detector with minimal dose deposition.
The final workflow includes the acquisition of cone-beam computed tomography scans and planar X-ray images before the irradiation to receive anatomical information and perform a treatment planning. The hippocampus as target region for current mouse brain irradiation experiments can be determined by registration with mouse brain atlas data. Proton radiography is acquired with a scattered proton beam right before the irradiation, resulting in a radiograph, which can be registered to the X-ray image. Finally, the target volume can be aligned to the collimated proton beam for accurate brain irradiation, which was validated by immunohistochemical staining of DNA damage region.
The setup for proton radiography and mouse brain irradiation, parameters influencing the radiography quality and experimental data will be presented.