Proton computed tomography: Update on current status

Proton beams offer a high degree of 3D conformality in radiation therapy due to their physical characteristics. For treatment planning and image-guided radiation therapy, protons may also be used to provide the required electron density and anatomic information. One advantage of proton imaging is that it can utilize data from each individual proton that traverses the object making it very-dose efficient. Over the last few years, we have invested considerable efforts into conceptual, theoretical, and experimental studies of proton computed tomography (pCT). In this contribution, we will give an update on the outcomes of these studies and the current status of the pCT project. In particular, a prototype pCT setup consisting of a silicon microstrip tracker and cesium iodide calorimeter installed on one of research beam tines of the Loma Linda Medical Center clinical proton accelerator will be described and first results obtained with this prototype with a 100-MeV proton beam will be presented. The additional utilization of new-generation pCT scanners for on-line proton dose verification and tumor imaging with positron emission tomography (PET) is suggested.