Extension of In-Beam PET to 4D for QA of motion-mitigated ion therapy

The in-beam PET camera has been operated in combination with beam tracking [2]. A homogeneous PMMA phantom was placed in the center of the field of view of the scanner and moved parallel to the two detector heads (left-right in beam’s eye view with 3 cm peak-to-peak amplitude and ≈ 3 s period). The prescribed dose was a twodimensionally spread-out Bragg-peak (SOBP) of 5×5 cm extension, centered at a depth of 10 cm in the central plane of the phantom. The list-mode PET acquisition was performed during the 6 min of beam delivery and for 25 min after irradiation (MOV). The data stream was synchronized with the time course of the dynamic beam application and with the motion monitor [2]. Additional 18 min of decay were acquired with the activated phantom kept steady (STAT), for comparison with a separate measurement of the same treatment field without motion (REF). For time-resolved reconstruction, the reconstruction algorithm [3] has been extended to distribute events to the different phases of the motion trajectory, including attenuation and solid angle corrections for moving geometries.