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.
