Abstract. Due to the tolerances given by the linear accelerator (LINAC) producer regarding the variability of mechanical movements, this work is focused on the influences of the mechanical components position in relative dose measurements such as percentage depth-dose distributions (PDD) and dose profiles. Those measurements represent an essential role in modelling the radiation beam accurately in the treatment planning system (TPS), such that the radiation therapy treatments can be delivered as intended. The main aspects of this work are to estimate the measurement uncertainty itself by statistical means and to provide a practical workflow to be performed prior to starting the dosimetric measurements.

Key words: Relative dose measurements, scanning system, beam modelling, linear accelerator.