A particle therapy system comprising: a particle generating apparatus for generating and accelerating irradiation particles; a beam generating apparatus for generating a particle beam from at least a portion of the generated irradiation particles; a detection apparatus for an automatic detection of a particle beam intensity of the particle beam; a grid control that is configured to sequentially irradiate grid points with the particle beam in accordance with a predefined irradiation plan, with the irradiation plan associating a respective desired value for the particle beam intensity to each of the grid points; and a particle beam influencing apparatus that is coupled to the grid control and that is configured to influence the particle beam intensity in dependence on the detected particle beam intensity and on the respective predefined desired value for the particle beam intensity of the grid point to be irradiated, characterized by a quality determination apparatus for determining a piece of quality information of the particle generating apparatus, with the quality determination apparatus being configured: to detect a control value that is output by the particle beam influencing apparatus to a control circuit for influencing the beam generating apparatus; to record the control values detected over the course of time together with the desired values for the particle beam intensity; and to derive a quality parameter for the function of the particle generating apparatus by evaluating a point of time of the reaching of a limit value of the detected control values. a particle generating apparatus for generating and accelerating irradiation particles; a beam generating apparatus for generating a particle beam from at least a portion of the generated irradiation particles; a detection apparatus for an automatic detection of a particle beam intensity of the particle beam; a grid control that is configured to sequentially irradiate grid points with the particle beam in accordance with a predefined irradiation plan, with the irradiation plan associating a respective desired value for the particle beam intensity to each of the grid points; and a particle beam influencing apparatus that is coupled to the grid control and that is configured to influence the particle beam intensity in dependence on the detected particle beam intensity and on the respective predefined desired value for the particle beam intensity of the grid point to be irradiated, characterized by a quality determination apparatus for determining a piece of quality information of the particle generating apparatus, with the quality determination apparatus being configured: to detect a control value that is output by the particle beam influencing apparatus to a control circuit for influencing the beam generating apparatus; to record the control values detected over the course of time together with the desired values for the particle beam intensity; and to derive a quality parameter for the function of the particle generating apparatus by evaluating a point of time of the reaching of a limit value of the detected control values. to detect a control value that is output by the particle beam influencing apparatus to a control circuit for influencing the beam generating apparatus; to record the control values detected over the course of time together with the desired values for the particle beam intensity; and to derive a quality parameter for the function of the particle generating apparatus by evaluating a point of time of the reaching of a limit value of the detected control values.