A Two-Plane Proton Radiography System Using ATLAS IBL Pixel-Detector Modules

Accurate knowledge of a patient’s anatomy during every treatment fraction in proton therapy is an important prerequisite to ensure a correct dose deposition in the target volume. Adaptive proton therapy aims to detect those changes and adjust the treatment plan accordingly. One way to trigger a daily re-planning of the treatment is to take a proton radiograph from the beam’s-eye view before the treatment to check for possible changes in the water equivalent thickness (WET) along the path due to daily changes in the patient’s anatomy. In this paper, the Two-Plane Imaging System (TPIS) is presented, comprising two ATLAS IBL silicon pixel-detector modules developed for the tracking detector of the ATLAS experiment at CERN. The prototype of the TPIS is described in detail, and proof-of-principle WET images are presented, of two-step phantoms and more complex phantoms with bone-like inlays (WET 10 to 40 mm). This study shows the capability of the TPIS to measure WET images with high precision. In addition, the potential of the TPIS to accurately determine WET changes over time down to 1 mm between subsequently taken WET images of a changing phantom is shown. This demonstrates the possible application of the TPIS and ATLAS IBL pixel-detector module in adaptive proton therapy.