It is an object of the invention to provide for a system, method and computer program product enabling monitoring of effects of intrafraction motion during the radio therapy treatment. According to a first aspect of the invention this object is achieved by an ultrasound guided radiotherapy system, comprising a radiotherapy system configured for providing a radiation treatment by means of a radiation beam to a treatment target. The ultrasound guided radiotherapy system further comprises an ultrasound imaging system configured for acquiring a 3D online image of the treatment target and/or an organ at risk during the radiation treatment. It further comprises detection means configured for detection, in the 3D online image, parts representing the treatment target and/or organ at risk and selection means configured for selecting a view plane through the treatment target and/or an organ at risk represented by the detected parts in the 3D online image and a display configured to display a 2D image of part of the treatment target and/or organ at risk along the view plane, wherein the display is further configured to display a treatment margin and/or an outline of an actual radiation beam in relation to the treatment target and/or organ at risk.