A therapeutic apparatus (500, 600) comprising a radiotherapy apparatus (502) for treating a target zone (318, 536) and a magnetic resonance imaging system (510, 532, 44, 602) for acquiring magnetic resonance imaging data (624). The radiotherapy apparatus comprises a radiotherapy source (300, 302, 304, 504) for directing electromagnetic radiation (310, 312, 314, 508) into the target zone. The radiotherapy apparatus is adapted for rotating the radiotherapy source at least partially around the magnetic resonance magnet. The magnetic resonance imaging system further comprises a radio-frequency transceiver (532) adapted for simultaneously acquiring the magnetic resonance data from at least two transmit-and-receive channels (528, 530). The therapeutic apparatus further comprises a processor (614) and a memory (620) containing machine executable instructions (636, 638, 640, 642, 644) for the processor. Execution of the instructions causes the processor to: calibrate (100, 200) the transmit-and-receive channels； acquire (102, 202) the magnetic resonance data； reconstruct (104, 204) a magnetic resonance image (626)； register (106, 206) a location (628) of the target zone in the image； and generate (108, 208) radiotherapy control signals (630) using the registered image.
