A particle therapy system (400, 602, 910) comprising: a particle accelerator (10, 105, 402, 604, 912) configured to output pulses of charged particles forming a beam of charged particles, wherein the particle accelerator is configured to output the pulses of charged particles in accordance with a radio frequency cycle; and a scanning system (106, 916) adapted to scan the beam across at least part of an irradiation target, the scanning system comprising: a scanning magnet adapted to move the beam during scanning, where a position of the beam corresponds to a current of the scanning magnet; characterised by: a control system adapted: (i) to control the current in order to produce uninterrupted movement of the beam across at least part of an irradiation target to deliver doses of the charged particles, wherein the uninterrupted movement of the beam across the at least part of an irradiation target is not dependent upon the radio frequency cycle, (ii) for positions at which the particle beam delivers dose, to store information identifying a location and an amount of dose delivered, wherein the control system is configured to measure the cumulative dose delivered at each position, wherein measuring is substantially synchronous with the radio frequency cycle, (iii) to compare a cumulative dose delivered at each position to a target cumulative dose, and (iv) if the cumulative dose does not match the target cumulative dose at specific positions, control the current in order to move the beam so as to deliver additional dose to the specific positions. a particle accelerator (10, 105, 402, 604, 912) configured to output pulses of charged particles forming a beam of charged particles, wherein the particle accelerator is configured to output the pulses of charged particles in accordance with a radio frequency cycle; and a scanning system (106, 916) adapted to scan the beam across at least part of an irradiation target, the scanning system comprising: a scanning magnet adapted to move the beam during scanning, where a position of the beam corresponds to a current of the scanning magnet; characterised by: a control system adapted: (i) to control the current in order to produce uninterrupted movement of the beam across at least part of an irradiation target to deliver doses of the charged particles, wherein the uninterrupted movement of the beam across the at least part of an irradiation target is not dependent upon the radio frequency cycle, (ii) for positions at which the particle beam delivers dose, to store information identifying a location and an amount of dose delivered, wherein the control system is configured to measure the cumulative dose delivered at each position, wherein measuring is substantially synchronous with the radio frequency cycle, (iii) to compare a cumulative dose delivered at each position to a target cumulative dose, and (iv) if the cumulative dose does not match the target cumulative dose at specific positions, control the current in order to move the beam so as to deliver additional dose to the specific positions. a scanning magnet adapted to move the beam during scanning, where a position of the beam corresponds to a current of the scanning magnet; characterised by: a control system adapted: (i) to control the current in order to produce uninterrupted movement of the beam across at least part of an irradiation target to deliver doses of the charged particles, wherein the uninterrupted movement of the beam across the at least part of an irradiation target is not dependent upon the radio frequency cycle, (ii) for positions at which the particle beam delivers dose, to store information identifying a location and an amount of dose delivered, wherein the control system is configured to measure the cumulative dose delivered at each position, wherein measuring is substantially synchronous with the radio frequency cycle, (iii) to compare a cumulative dose delivered at each position to a target cumulative dose, and (iv) if the cumulative dose does not match the target cumulative dose at specific positions, control the current in order to move the beam so as to deliver additional dose to the specific positions. (i) to control the current in order to produce uninterrupted movement of the beam across at least part of an irradiation target to deliver doses of the charged particles, wherein the uninterrupted movement of the beam across the at least part of an irradiation target is not dependent upon the radio frequency cycle, (ii) for positions at which the particle beam delivers dose, to store information identifying a location and an amount of dose delivered, wherein the control system is configured to measure the cumulative dose delivered at each position, wherein measuring is substantially synchronous with the radio frequency cycle, (iii) to compare a cumulative dose delivered at each position to a target cumulative dose, and (iv) if the cumulative dose does not match the target cumulative dose at specific positions, control the current in order to move the beam so as to deliver additional dose to the specific positions.