Ultrasonically-stimulated microbubbles can enhance cell membrane permeability and decrease cell viability where the underlying acoustic mechanism has been associated with both non-inertial and inertial cavitation. In this study, breast cancer cells (MDA-MB-231) were exposed to 0.5MHz ultrasound pulses of 16μs duration at varying peak negative pressures (PNP: 218kPa, 335kPa and 908kPa) and pulse repetition period (PRP 10ms and 100ms) in the presence of Definity microbubbles (3.3% v/v). The acoustic response of microbubbles was measured using passive cavitation detection with 2.25MHz transducer, and characterized by their frequency a cavitation dose (CD). Results show that the number of non-viable cells and integrated cavitation dose (ICD) significantly increases with PNP, whereas no significant differences were found between 10ms and 100ms PRPs. In this study, no correlation was found between (ICD) and cell non-viability.