Power density requirement of a 4 MHz micro-ultrasonic transducer for sonodynamic therapy

In this paper, we propose the use of micro-ultrasonic transducers (MUTs) for a therapeutic application in combination with a cancer drug. In particular, sonodynamic enhancement of doxorubicin cytotoxicity was investigated in vitro using human prostate cancer cells (PC3). Cells in suspensions were found to be two to three times more prone to the cytotoxic effect of ultrasound than adherent cells. With 60 s of tone-burst ultrasound (4 MHz, 50 ms repetition period, and 25% duty cycle) at 40 Watt/cm(2) (spatial average-temporal average), cytotoxicity of doxorubicin treatment of adherent cells increased from 27 to 91%. The threshold ultrasonic power density required for any cytotoxicity enhancement to be observable was found to be 15 Watt/cm(2) for PC3 cells with doxorubicin and tone burst ultrasound at 4 MHz. This is a level achievable by MUTs. The long term vision is to design implantable MUTs for sonodynamic therapy with the goal of improving treatment efficacy.