The invention provides for a medical apparatus (200, 300, 400) comprising: a magnetic resonance imaging system (202), a display (270), a processor (228), and a memory (234) for storing instructions for the processor. The instructions causes the processor to receive a brachytherapy treatment plan (240), acquire (100) planning magnetic resonance data (244), calculate (102) a catheter placement positions (246, 900, 902) and a catheter control commands (248) the brachytherapy catheters. The instructions cause the processor, for each catheter placement position, to repeatedly: acquire (106) guidance magnetic resonance data (250), reconstruct (108) an image (252, 500), display (110) the image and the catheter placement position on the display, receive (114) a catheter inserted signal from a user interface, segment (116) the image to determine the catheter placement position after receiving the catheter inserted signal, recalculate (116) the catheter placement positions for each remaining catheter placement position after receiving the catheter inserted signal, and recalculate (116) the catheter control command for all of the multiple catheters after receiving the catheter inserted signal.