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.