A charged particle irradiation system comprising: an accelerator for extracting a charged particle beam; a control unit; and an irradiation nozzle comprising a beam scanning equipment (24, 25) and a beam position monitor system (26, 27); wherein the beam position monitor system (26, 27) comprises a first position monitor disposed upstream of the beam scanning equipment (24, 25) and a second position monitor disposed downstream of the beam scanning equipment (24, 25) and is configured to measure an actual position (xA) and an actual angle (θ1) of the beam injected into the nozzle, and wherein said control unit is configured to calculate a difference (δx) of an expected irradiation position with respect to a desired irradiation position at the target position, said difference (δx) being caused by deviations of the actual position (xA) and the actual angle (θ1) of the injected beam with respect to ideal conditions, based on information provided by the beam position monitor system (26, 27), and to account for said deviations by correcting the value of an excitation current applied to the beam scanning equipment (24, 25) in order to move the beam from the expected irradiation position to a desired irradiation position at the target position by the amount of the calculated difference (δx). an accelerator for extracting a charged particle beam; a control unit; and an irradiation nozzle comprising a beam scanning equipment (24, 25) and a beam position monitor system (26, 27); wherein the beam position monitor system (26, 27) comprises a first position monitor disposed upstream of the beam scanning equipment (24, 25) and a second position monitor disposed downstream of the beam scanning equipment (24, 25) and is configured to measure an actual position (xA) and an actual angle (θ1) of the beam injected into the nozzle, and wherein said control unit is configured to calculate a difference (δx) of an expected irradiation position with respect to a desired irradiation position at the target position, said difference (δx) being caused by deviations of the actual position (xA) and the actual angle (θ1) of the injected beam with respect to ideal conditions, based on information provided by the beam position monitor system (26, 27), and to account for said deviations by correcting the value of an excitation current applied to the beam scanning equipment (24, 25) in order to move the beam from the expected irradiation position to a desired irradiation position at the target position by the amount of the calculated difference (δx). to calculate a difference (δx) of an expected irradiation position with respect to a desired irradiation position at the target position, said difference (δx) being caused by deviations of the actual position (xA) and the actual angle (θ1) of the injected beam with respect to ideal conditions, based on information provided by the beam position monitor system (26, 27), and to account for said deviations by correcting the value of an excitation current applied to the beam scanning equipment (24, 25) in order to move the beam from the expected irradiation position to a desired irradiation position at the target position by the amount of the calculated difference (δx).