Abstract: The present invention concerns a method for assessing a quality of a beam shaping device (11) manufactured according to a planned device design (11d) for shaping a beam (100.i) of accelerated particles emitted by a particle accelerator system, the method comprising, (a) establishing with a treatment planning system (TPS) the planned device design (11d) of the beam shaping device, (b) manufacturing the beam shaping device according to the planned device design, (c) establishing a CT-scan of the beam shaping device to yield an actual CT-image (11a), (d) determining dimensions and local materials densities from the actual CT-image, (e) determining a calculated dose distribution in the treatment volume (V) obtained by virtually irradiating the treatment volume with the beam through a virtual beam shaping device having a geometry and a density defined by the device actual CT-image, (f) comparing the calculated dose distribution (cDD) with a reference dose distribution (rDD).