A medical apparatus (200, 300, 400) comprising: - A magnetic resonance imaging system for acquiring magnetic resonance data (244, 250) from an imaging zone; - a display (270, 501) for displaying images (252, 500); - a processor for controlling the medical apparatus; - a memory for storing machine executable instructions for execution by the processor, wherein execution of the instructions causes the processor to receive a brachytherapy treatment plan for treating a subject, wherein execution of the instructions further causes the processor to acquire planning magnetic resonance data using the magnetic resonance imaging system, wherein execution of the instructions further causes the processor to calculate a catheter placement position (246, 900, 902) and a catheter control command for each of the multiple brachytherapy catheters using the brachytherapy treatment plan and the planning magnetic resonance data, wherein the catheter control command is descriptive of locations for one of the multiple brachytherapy catheters, wherein execution of the instructions causes the processor, for each catheter placement position, to repeatedly: - acquire guidance magnetic resonance data; - reconstruct an image (252, 500) from the guidance magnetic resonance data; - display the image on the display; - display the catheter placement position on the image; - receive a catheter inserted signal from a user interface; - segment the image to determine the catheter placement position after receiving the catheter inserted signal; - recalculate the catheter placement positions for each remaining catheter placement position after receiving the catheter inserted signal; and - recalculate the catheter control command for the multiple catheters after receiving the catheter inserted signal characterised in that: the catheter control command is descriptive of dwell times for the locations for one of the multiple brachytherapy catheters; at least one of the multiple brachytherapy catheters (1500, 1600, 1700, 1800) is configured for generating an anisotropic radiation field, wherein the catheter control command is further descriptive of a rotational position of the anisotropic radiation field of the brachytherapy catheter for each of the dwell times and the medical apparatus further comprises a catheter actuator (302, 2206, 2208) configured for controlling the position and the rotational position of the anisotropic radiation field of each of the multiple brachytherapy catheters as a function of time, wherein execution of the instructions further causes the processor to control the position of the multiple brachytherapy catheters as a function of time with the catheter actuator in accordance with the catheter control commands. - A magnetic resonance imaging system for acquiring magnetic resonance data (244, 250) from an imaging zone; - a display (270, 501) for displaying images (252, 500); - a processor for controlling the medical apparatus; - a memory for storing machine executable instructions for execution by the processor, - acquire guidance magnetic resonance data; - reconstruct an image (252, 500) from the guidance magnetic resonance data; - display the image on the display; - display the catheter placement position on the image; - receive a catheter inserted signal from a user interface; - segment the image to determine the catheter placement position after receiving the catheter inserted signal; - recalculate the catheter placement positions for each remaining catheter placement position after receiving the catheter inserted signal; and - recalculate the catheter control command for the multiple catheters after receiving the catheter inserted signal the catheter control command is descriptive of dwell times for the locations for one of the multiple brachytherapy catheters; at least one of the multiple brachytherapy catheters (1500, 1600, 1700, 1800) is configured for generating an anisotropic radiation field, wherein the catheter control command is further descriptive of a rotational position of the anisotropic radiation field of the brachytherapy catheter for each of the dwell times and the medical apparatus further comprises a catheter actuator (302, 2206, 2208) configured for controlling the position and the rotational position of the anisotropic radiation field of each of the multiple brachytherapy catheters as a function of time, wherein execution of the instructions further causes the processor to control the position of the multiple brachytherapy catheters as a function of time with the catheter actuator in accordance with the catheter control commands.