A particle therapy delivery system 200 comprising: a rotatable support structure 12 defining a patient enclosure； and a particle delivery line 22 for delivering particles to a patient. The particle delivery line 22 comprises at least one linear particle accelerator / linac 14 mounted to the support structure so that particles travelling along the particle delivery line 22 complete at least one revolution about an axis of the support structure 12. System 200 may comprise at least one guiding device 16 producing an electromagnetic field that alters the path of particles travelling along the particle delivery line 22, where guiding device 16 may receive particles from and/or transmit particles to the at least one linear accelerator 14. The particle delivery line 22 may comprise a plurality of spaced apart linear particle accelerators 14, where at least one guiding device 16 is located between adjacent linear particle accelerators 14 and where the linear particle accelerators 14 may be mounted to the support structure 12 in a substantially helical manner. System 200 may comprise a pre-accelerator 18 providing pre-accelerated particles to the particle delivery line 22. System 200 may comprise a bypass particle line 42 for bypassing the particle delivery line 11.
