An apparatus for delivery of spatially fractionated radiation treatment to a patient, the apparatus comprising: a radiation source for generating an open radiation beam oriented along a beam axis and having photon energies up to and including a maximum photon energy greater than 0.5 MV; a mini-beam collimator located in a path of the open radiation beam, the mini-beam collimator comprising a plurality of generally planar blades extending between an entrance aperture onto which the open beam impinges and an exit aperture, the mini-beam collimator interacting with the open radiation beam to produce an output beam emitted from the exit aperture, oriented along the beam axis and comprising a spatially fractionated mini-beam dose profile, the spatially fractionated mini-beam dose profile comprising: a plurality of dose peaks at which the dose is a local maximum, the dose peaks spaced apart from one another in a transverse direction that is transverse to the beam axis; and a plurality of dose valleys at which the dose is a local minimum, each dose valley located between a pair of transversely adjacent dose peaks.