The biological focal region (BFR) induced by a single high-intensity focused ultrasound (HIFU) exposure is considered to be the foundation of the ultrasound ablation of tumor lesions. The purpose of this study was to explore the relationship between the acoustic focal region (AFR) and the BFRs with different combinations of power and time in low-power cumulative HIFU treatment. The finite-difference time-domain (FDTD) method was used to simulate AFR and BFR during HIFU ablation. The acoustic fields, the temperature profiles, and the shapes of BFRs were calculated by the Westervelt equation, Pennes’ equation, and the equivalent thermal dose model. In order to verify the simulation rules, phantom and ex vivo bovine livers were exposed by HIFU with a different power and time. The results demonstrated that in the low-power cumulative HIFU treatment, when the lengths of BFRs and the length of AFR were approximately equal, the shape of the BFR induced by ‘high power × short time’ exposure was closer to that of AFR than the shape of the BFR induced by ‘low power × long time’ exposure, and the exposure energy required was significantly reduced. The analysis revealed the relationship between the BFR and the AFR with different acoustic power. This study provides a reference for doctors to determine power, time, and movement distance in clinical treatment.

High-intensity focused ultrasound (HIFU) ablation has been widely used in advanced pancreatic cancer in recent years. In numerous studies, HIFU has been shown to be safe, effective, and practicable, but there are a few HIFU-related adverse effects. The patients’ discomfort during therapy increased proportionally with increasing delivered energy and pain levels seemed to be independent of the dose of anesthetic or sedation. If the power used in therapy is too high, the temperature of the target area will rise rapidly, and the boiling and cavitation make the shape of the necrosis area difficult to control. In recent years, moderate-intensity focused ultrasound (MIFU) has also been shown to heat the tumor locally for palliative treatment. Choosing the appropriate power and effectively controlling the tissue temperature until reaching the threshold for thermal necrosis are of great significance for ensuring the safety of palliative treatment. In this study, an infrared temperature measurement experimental system was set up to measure the temperature rise at different power in an ex vivo bovine liver. It was found that when the acoustic intensity of the focused ultrasound was lower than the cavitation threshold (within the range of the MIFU), the temperature of the tissue kept rising at a steady rate and could still reach the thermal damage threshold temperature within tens of seconds. The results showed that the temperature induced by the MIFU was almost entirely dependent on the thermal effect, and the temperature of the tissue at the end of sonication was linearly related to the power. Finally, this study considered the effect of blood perfusion on the temperature for the application of focused ultrasound in the palliative treatment of advanced pancreatic cancer with the goal of providing a reference for the application of focused ultrasound in the palliative treatment of advanced pancreatic cancer.