Fig. 2: Experimental beamline.

a, Drawing of the different elements along the experimental beamline. The mice were irradiated in a vertical position inside the SIRMIO PET scanner while a series of passive components shaped the beam to match the desired irradiation volume. In particular, calibrated large-plate ionization chambers were used as beam monitors for the pristine ¹¹C beam. A 2D range modulator shaped the beam energy, creating a 1.2-cm SOBP in water. A range shifter and aluminium degraders were then used to adjust the beam range to approximately match the tumour position. Two brass collimators were used to reduce the lateral irradiation field and block parts of the beam that did not contribute to the target dose. Finally, a plastic mouse collar acting as a compensator was fixed to the mouse bed. It was designed to partially absorb the beam outside the CTV and shape the distal edge of the SOBP to match the target contour. b, SIRMIO animal holder with the anaesthesia tubes and a mouse in position. c, Animal holder aligned in the beamline while the SIRMIO PET is raised. d, The SIRMIO PET scanner is then lowered to surround the animal. e, Lateral view of the full beamline. Panel a created with BioRender.com.