Effect of Beam Size on Stone Comminution in Shock Wave Lithotripsy

The effect of beam size on stone comminution in the Dornier HM-3 lithotripter were investigated using a modified reflector (MR), which was developed to produce an acoustic field with higher peak pressure and smaller beam size compared to the original reflector (OR) of the HM-3. The acoustic fields produced at 20 kV by the MR in the focal plane, and by the OR in the focal and pre-focal plane (z = -15 mm) were characterized using a light spot hydrophone. The efficiencies of stone comminution in a mesh holder were similar, but the corresponding values produced by using the MR in a membrane holder were significantly lower than those produced by the OR in the focal and pre-focal planes. These results suggest that a broad beam size could increase stone comminution efficiency when fragments are spreading out or moving due to respiratory motion in a large area during SWL. In contrast, when stone fragments are confined and well aligned to lithotripter focus the beam size may not influence significantly the treatment outcome.