A safety-catch mechanism for a fiducial-deployment system, having a main handle, a stylet, a guide sleeve, and a grasping handle for moving adjacent to the guide sleeve. One of the guide sleeve or grasping handle has a threaded surface, and the other has one or more protruding tabs to rotatably engage between the threads. A safety-catch structure is located between the threads and configured to resist rotation of the grasping handle when one of the protruding tabs contacts this structure, unless the user applies a threshold amount of mechanical force to overcome this safety-catch structure, permitting distal movement of the stylet.
