Methods and apparatus are provided for loading therapeutic materials into brachytherapy needles. The apparatus comprises a loading tube with a lumen and two transverse slots, and radioactive seed and spacer cartridges slidably received within the transverse slots. The apparatus may be used in conjunction with a standard brachytherapy plunger and needle coupled to, respectively, the proximal and distal ends of the loading tube. The plunger dislodges seeds and spacers from the cartridge chambers to load the needle with a predetermined packing arrangement.