Development of a list-mode data acquisition system for prompt X-ray imaging during irradiation with carbon-ions

Prompt X-ray imaging using a low-energy X-ray camera is a promising method for observing the beam shape from outside the subject. However, such imaging has so far been conducted only on static images with relatively long acquisition times without any energy information. Consequently, we performed list-mode prompt X-ray imaging using a newly developed data acquisition system combined with a pinhole YAP(Ce) camera during irradiation of a water phantom with carbon ions. Prompt X-ray imaging was conducted in list mode with a 1-ms time stamp and 128-channel energy bins during irradiation of a water phantom with 241.5 MeV/n carbon ions. After the imaging, list-mode data were sorted to obtain the time-sequential prompt X-ray images and those with different energies. From the images with different energies, we found the energy spectra were different depending on the areas in the images, and the reduction of the background fraction was possible. From the short time-sequential prompt X-ray images, we could even observe the differences in the images depending on the acquisition times, as well as the spill and ripple shapes of the carbon ion beam.