Fig. 1.

Schematic representation of the density override strategies adapted from [5]. (left) Free-breathing CT (FBCT). (middle) Density override strategy DO1: the density of the PTV is replaced by the mean density of the GTV. (right) Density override strategy DO2: the density of the ITV is replaced by the mean density of the GTV and the density of the remaining PTV is set to the average density between the mean GTV density and the surrounding tissue described by the mean density of a 5 mm margin surrounding the PTV (MPTV_+5mm).