The invention relates to an assisting apparatus for assisting in performing brachytherapy. The position of an introduction element (17) like a catheter is tracked particularly by using electromagnetic tracking, while a group of seeds is introduced into a living object (2). This provides a rough knowledge about the position of the seeds within the object. An ultrasound image showing the group is generated depending on the tracked position of the introduction element and, thus, depending on the rough knowledge about the position of the seeds, in order to optimize the ultrasound visualization with respect to showing the introduced seeds. Based on this optimized ultrasound visualization the position of a seed of the group is determined, thereby allowing for an improved determination of seed positions and correspondingly for an improved brachytherapy performed based on the determined positions.