Extended Data Fig. 7: Simulation of PET imaging of a RIB damaging the spinal cord.

a. FLUKA simulation showing a hypothetical case of a¹¹C-ion SOBP dose (in Gy) distribution damaging the spinal cord for a vertical CBCT SARRP scan of a mouse in the axial view (shown in the background). Doses are normalized to the planned target dose. b. Corresponding Monte Carlo simulation of the PET activity as should have been seen with the SIRMIO PET scanner, overlaid on the same axial SARRP slice for the same mouse (displayed in the background). c. The activity simulation shown in b is now overlaid on the µCT scan (in the axial view, shown in the background) of the same mouse to illustrate what we would have seen online in case of RIB range exceeding the target distal position. The generalized CTV contour (Fig. 1) is highlighted with a black line, while the OAR contour is marked in red. All the images are integrated over the BEV aperture in the y-plane transversing the beam direction. In panels d, e, the same sagittal SARRP slice of the mouse is shown in the background of the 2D distributions. In panel f, the sagittal view of the µCT scan is displayed in the background. g. The corresponding simulated dose normalized to the target dose (solid black) and the simulated PET activity (dashed black) depth profiles, normalized to their maximum, along the z-axis direction, integrated over the BEV aperture in the x-y plane transversing the beam direction. The CTV and spine regions are highlighted by pink and red bands, respectively, while the compensator is depicted in yellow and the dimple in light blue. The plot shows that an online image as depicted in panels c and f, never actually observed in our experiments, would have required the insertion of a range shifter to reduce the range during the irradiation.