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.