Results from a pre-clinical head scanner for proton CT

We report on the first beam test results with our pre-clinical (Phase-II) head scanner developed for proton computed tomography (pCT). After extensive preclinical testing, pCT will be employed in support of proton therapy treatment planning and pre-treatment verification in patients undergoing treatment with particle beam therapy. The Phase-II pCT system consists of two silicon-strip telescopes that track individual protons before and after the phantom or patient, and a novel multistage scintillation detector that measures a combination of the residual energy and range of the proton, from which we derive the water equivalent path length (WEPL) of the protons in the scanned object. The set of WEPL values and associated paths of protons passing through the object over a 360° angular scan is processed by an iterative, parallelizable reconstruction algorithm that runs on modern GP-GPU hardware. In order to assess the performance of the scanner, we have performed beam tests with 200 MeV protons from the synchrotron of the Loma Linda University Medical Center. The first objective was the calibration of the instrument, including tracker channel maps and alignment as well as the WEPL calibration. Then we performed the first CT scans on a series of phantoms. The very high sustained rate of data acquisition, exceeding one million protons per second, allowed a full 360° scan to be completed in less than 10 minutes, and reconstruction of a CATPHAN 404 phantom verified accurate reconstruction of the proton relative stopping power in a variety of materials.