A high-energy radiation treatment system can comprise a laser-driven accelerator system, a patient monitoring system, and a control system. The laser-driven accelerator system, such as a laser-driven plasma accelerator or a laser-driven dielectric microstructure accelerator, can be constructed to irradiate a patient disposed on a patient support. The patient monitoring system can be configured to detect and track a location or movement of a treatment volume within the patient. The control system can be configured to control the laser-driven accelerator system responsively to the location or movement of the treatment volume. The system can also include a beam control system, which generates a magnetic field that can affect the radiation beam and/or secondary electrons produced by the irradiation beam. In some embodiments, the beam control system and the patient monitoring system can comprise a magnetic resonance imaging system.