EFFECTS OF ENERGY-MATCHED PULSED AND CONTINUOUS ULTRASOUND ON TUMOR-GROWTH IN MICE

Background and Purpose. A diagnosis of cancer is a contraindication fo r the use of therapeutic ultrasound (US). Continuous US applied to mur ine tumors has resulted in larger and heavier tumors compared with con trols. We compared tumor growth using low-power continuous US and ener gy-matched pulsed US. Subjects. Female C57BL/6 mice (N=174) were used. Methods. Animals received subcutaneous injections of methylcholanthre ne tumor cells. The mice were randomly divided into three groups: 60 m ice that received low-power continuous US for 5 minutes at 0.75 W/cm(2 ) (LC US group), 63 mice that received pulsed US for 12.5 minutes at 1 .5 W/cm(2) (pulsed US group), and 51 mice that served as a control gro up. The LC and pulsed US groups received equal US energy. Both experim ental groups received 10 treatments of 3-MHz US, which was applied dir ectly over the tumor. The control group received identical handling bu t no US. After treatment, the tumors were excised, weighed, and measur ed. A one-way analysis of variance, followed by Newman-Keuls Post hoc testing, was used to analyze the data. Results. Mean tumor weights (in grams) and volumes (in cubic millimeters) were 0.563 g and 564 mm(3) for the LC US group, 0.560 g and 525 mm(3) for the pulsed US group, an d 0.516 g and 406 mm(3) for the control group. Conclusion and Discussi on. Reducing total US energy will result in less growth of murine tumo rs. When infusing equal energy, continuous and pulsed US will produce similar effects on tumor growth.