The present disclosure relates to a method for controlling a magnetic resonance imaging guided radiation therapy apparatus (100) comprising a magnetic resonance imaging system (106). The method comprises: acquiring magnetic resonance data using the magnetic resonance imaging system from an organ (146), the organ being marked by a predefined marker; the magnetic resonance data comprising 3D image data; identifying in a reconstructed 2D image of the magnetic resonance data at least one signal void candidate of the marker; processing the 3D image data and the identified signal void for calculating a likelihood that the identified signal void candidate is part of the marker; outputting an indication of the calculated likelihood; in response to the outputting, receiving a user input specifying performing a radio therapy; and controlling the irradiation of the organ using the radiation therapy.