2nd ESTRO Forum 2013 S481 motion (gantry period = 2x motion period) are the most challenging, since each position of the sphere, along its trajectory, is imaged under the same angle during the whole acquisition. In this particular setting, motion information is missing in the MV-CT (see figure) and non-negligible registration errors were observed in LR tumor motion (>4.4 mm) with all methods. No significant registration errors have been observed for other motions.