A radiotherapy apparatus, comprising: a megavolt radiation source that is configured to emit radiation that traverses an examination region and a two-dimensional energy-resolving detector array that is configured to detect radiation emitted by the megavolt radiation source that traverses the examination region; a kilovolt source that is configured to emit ionizing radiation that traverses the examination region and a two-dimensional energy-resolving detector array that is configured to detect ionizing radiation emitted by the kilovolt radiation source that traverses the examination region; the apparatus being characterised by further comprising: a tissue of interest tracker that is configured to receive a first image of tissue of interest and a second later acquired spectral image of the tissue of interest and configured to track a change in a geometry and/or location of the tissue of interest based at least on the first and second images and generates a signal indicative of the change, wherein the second later acquired spectral image is generated based on a first spectral signal corresponding to an output of one of the two-dimensional energy-resolving detector arrays (110, 114) for a first predetermined energy range and a second spectral signal corresponding to an output of one of the two-dimensional energy-resolving detector arrays (110, 114) for a second predetermined energy range, wherein the second later acquired spectral image visually enhances scanned structure corresponding to the first or second signals while visually suppressing other scanned structure corresponding to the other of the first or second signals; and an adaptive planner that is configured to update a radiotherapy treatment plan based on the signal indicative of the change from the tissue of interest tracker. a megavolt radiation source that is configured to emit radiation that traverses an examination region and a two-dimensional energy-resolving detector array that is configured to detect radiation emitted by the megavolt radiation source that traverses the examination region; a kilovolt source that is configured to emit ionizing radiation that traverses the examination region and a two-dimensional energy-resolving detector array that is configured to detect ionizing radiation emitted by the kilovolt radiation source that traverses the examination region; a tissue of interest tracker that is configured to receive a first image of tissue of interest and a second later acquired spectral image of the tissue of interest and configured to track a change in a geometry and/or location of the tissue of interest based at least on the first and second images and generates a signal indicative of the change, wherein the second later acquired spectral image is generated based on a first spectral signal corresponding to an output of one of the two-dimensional energy-resolving detector arrays (110, 114) for a first predetermined energy range and a second spectral signal corresponding to an output of one of the two-dimensional energy-resolving detector arrays (110, 114) for a second predetermined energy range, wherein the second later acquired spectral image visually enhances scanned structure corresponding to the first or second signals while visually suppressing other scanned structure corresponding to the other of the first or second signals; and an adaptive planner that is configured to update a radiotherapy treatment plan based on the signal indicative of the change from the tissue of interest tracker.