The invention provides a phantom and method for quality assurance of a particle therapy apparatus used in the intensity modulated particle therapy mode. The phantom comprises a frame structure one or more wedges a first and second block of material each having a first block face and a second block face parallel thereto an absolute dosimeter arranged at said first block face a plurality of beads of high density material located in said blocks and a 2D detector. The components are arranged in a known fixed position in relation to the frame structure. A central bead is maintained in a central known fixed position in relation to the frame structure. The components are arranged in the frame structure so that a beam will traverse the phantom, through the central bead, without traversing any material besides said central bead.
