Influence of the shock wave application mode on the growth of A-Mel 3 and SSK2 tumors in vivo.

We examined the influence of different shock wave application modes with a Dornier XL1 electrohydraulic lithotripter on the growth of A-Mel 3 and SSK2 tumors implanted under the dorsal skin of hamsters or mice. In a basic protocol, 500 shock waves a day on 4 consecutive days were administered at a discharge rate of 100 waves per minute and focused to the tumor center. This did not affect A-Mel 3 growth. A similar result was obtained with the basic protocol modified to 1000 shock waves a day and a wave application rate of 100 shock waves per second. Growth of A-Mel 3 and SSK2 tumors was significantly delayed, when the basic protocol was used, but the 500 shock waves a day were distributed over four points at the tumor edges and the tumor center. With the same shock wave protocol, lowering the water level over the tumor from 10 cm to 1 cm induced temporary regressions of SSK2 tumors. This was not due to the higher energy applied to the tumor, since twice the number of shock waves (1000 a day instead of 500 a day) was applied at a high water level and did not induce regressions. Four consecutive treatments with intervals between treatments shortened to 3 h and an additional treatment 12 h later at a low water level completely controlled tumor growth in 8 out of 12 SSK2 tumors for more than 150 days. The result showed that addition of a reflected wave from the water surface was most important for the shock wave effect, and suggested that shock wave devices generating similar wave forms should be applied for tumor therapy.