Introduction: Transient cavitations induced by low frequency irradiation of ultrasound can be used to treat tumors. Previous studies in in-vitro experiments have shown that induced cavitation by dual or multiple frequencies of ultrasound is greater than induced cavitation by single frequency irradiation. In this study, we compared and evaluated the treatment effects of dual frequency irradiation of ultrasound (1 MHz and 150 kHz) and single frequency irradiation in in-vivo experiments on breast adenocarcinoma tumors.
Material and Method: In this study, the tumor-bearing mice were divided into 5 groups: control, sham, treated group for 30 min with 150 kHz frequency in continuous mode, another group with 1 MHz frequency in pulse mode, and treated group with combined dual frequency ultrasound (150 kHz in continuous mode and 1 MHz in 80% pulse mode). To evaluate the effects of ultrasound irradiation on tumor growth delay, the volumes of the tumors were investigated for 30 days. Tumor growth delay parameters including relative volume, inhibition ratio percentage and the required times for the tumor volume to reach to two (T2) and five (T5) times its initial volume were calculated.
Results: The results showed that the treated groups with single frequency irradiation of 150 kHz continuous mode and 1 MHz pulse mode and combined dual frequency had statistically significant differences in tumor relative volume percentage during the period of 3 to 24 days after treatment (p<0.05). The percentage of tumor growth inhibition in the treated groups with dual frequency irradiation was significantly greater than the treated groups with single frequency irradiation, especially 3, 9 and 18 days after treatment. There were statistically significant differences between the T2 and T5 times of treated groups with dual frequency ultrasound irradiations compared to single frequency irradiations (p<0.05). The mean survival period for animals in the treated groups with single frequency of 150 kHz and dual frequency ultrasound irradiation were 85% greater than the control group.
Discussion and Conclusion:  It is concluded that simultaneous dual frequency irradiation is more effective than single frequency irradiation to control the growth of breast adenocarcinoma tumors.