Fig. 4: Activity profiles in mice.

a, For the same mouse in Fig. 3, we show the z-axis depth profiles of the simulated dose (normalized to the target dose; blue), the simulated PET activity (dashed blue) and the measured (solid red) PET activity profiles, normalized to their maximum and laterally integrated on the BEV aperture (±1 mm) in the x–y plane orthogonal to the beam direction. The CTV and µCT spine regions are highlighted by pink and red bands, respectively, while the compensator is depicted in yellow and the dimple (Extended Data Fig. 3b) in light blue. b, Comparison between simulated dose and PET activity profiles for a mouse analysed at the CBCT in the SARRP in vertical position. The plot shows the z-axis depth profiles of the simulated dose (normalized to the target dose; solid black), the simulated PET activity (dashed black), and the measured (solid red) PET activity profiles, normalized to their maximum and laterally integrated on the BEV aperture (±1 mm) in the x–y plane orthogonal to the beam direction. Although the mouse is not the same as in a, we observed that switching to the vertical position consistently induces the same anatomical change in all animals. Therefore, we overlaid the measured PET activity profile of the mouse from Fig. 3 in red. As in a, The CTV and SARRP spine regions are highlighted by pink and red bands, respectively, while the compensator is depicted in yellow and the dimple (Extended Data Fig. 3b) in light blue.