Method of operating an ion beam therapy system with monitoring of beam position

Method for the operation of an ion beam therapy system, having monitoring of the beam position, wherein the ion beam therapy system comprises

• at least one ion source (1)
• an accelerator device (2, 5) for the acceleration of the ions of the ion source (1) in the form of a treatment beam (11),
• a beam guidance system (6, 8), to guide the treatment beam (11) from the accelerator device (2, 5) to at least one irradiation site for treatment of a patient, the beam guidance system (6, 8) comprising at least one beam guidance channel (6), and
• a grid scanner device, arranged in the beam guidance system (6, 8), having vertical deflection means (13) and horizontal deflection means (14) for the vertical and horizontal deflection of the treatment beam (11) perpendicular to its beam direction, with the result that the treatment beam (11) is deflected by the grid scanner device to an isocentre (10) of the irradiation site and scans a specific area surrounding the isocentre (10),
• wherein the beam position of the treatment beam (11) in the region of the isocentre (10) is monitored and evaluated, and
• wherein intervention in the ion beam therapy system is carried out if the evaluation of the beam position shows a departure, from a predetermined desired value, that exceeds a specific tolerance value based on a required half-value width of the beam profile, and
• wherein the beam position of the treatment beam (11) is monitored online during performance of an irradiation procedure using a plurality of multi-wire chambers arranged spaced apart from one another, characterised in that
• the multi-wire chambers are arranged differently spaced from the isocentre (10) and so aligned that the treatment beam (11) extending through the isocentre (10) runs perpendicularly through the centre of the multi-wire chambers,
• an absolute zero point of the beam position and an absolute beam profile width of the treatment beam (11) being ascertained, and
• the multi-wire chambers being calibrated with respect to the absolute zero point and the absolute beam profile width of the treatment beam (11), the absolute zero point and the absolute beam profile width of the treatment beam (11) being determined with the aid of a verification film, which is irradiated with the treatment beam (11), and
• the absolute zero point determined with the aid of the verification film and the absolute beam profile width determined with the aid of the verification film being compared with an absolute zero point determined with the aid of the multi-wire chambers and with an absolute beam profile width determined with the aid of the multi-wire chambers, and
• the differences resulting from that comparison being taken into account, in the monitoring of the beam position of the treatment beam (11) by the multi-wire chambers, as correction offsets in the desired position values.