A therapeutic apparatus (400, 500) comprising a radiotherapy apparatus (402), a mechanical positioning system, and a magnetic resonance imaging system (404). The radiotherapy apparatus comprises a radiotherapy source (408). The radiotherapy apparatus is adapted for rotating the radiotherapy source at least partially around a subject support. The therapeutic apparatus further comprises a memory containing machine executable instructions (468, 470, 472, 474, 476). Execution of the instructions causes a processor to repeatedly: acquire (100) the magnetic resonance data using the magnetic resonance imaging system； reconstruct (102) a magnetic resonance image (460) from the magnetic resonance data； register (104) a location (462) of the target zone in the magnetic resonance image； generate (106) radiotherapy control signals (464) in accordance with the location of the registered target zone； generate (108) mechanical positioning control signals (466) in accordance with the registered target zone and the radiotherapy control signals； and send (110) the radiotherapy control signals to the radiotherapy system and send (110) the mechanical positioning control signals to the mechanical positioning system.
