Study Of HIFU Liver Tumor Therapy In Simulation&Vitro Experiment

As a non-invasive or minimally invasive cancer therapeutic technology through local high temperature was developed in recent years,high intensity focused ultrasound(HIFU)has been applied to the clinical treatment for solid tumor.However,due to many unsolved problems,such as the real-time temperature monitoring,therapeutic dose,residual tumor tissue and over-treatment will occur in the clinical treatment,the security and reliability of HIFU can not be guaranteed.It is severely restricted in the promotion of the clinical application.ObjectiveValidate the simulation method through the bovine vitro tissue experiment,research the temperature distribution of the HIFU focal region in liver tumor by numerical simulation,and then discuss the variation of the treatable focal region under the different therapeutic dose and how much dose of HIFU is required to form a same volume of treatable focal region.The results can provide the theoretical reference data and basis for the clinical HIFU therapeutic dose and treatment plan formulation.MethodsIn this study,the approximate of Westervelt Formula for the nonlinear propagation of HIFU proposed by Nagayoshi Moritato was adopt to calculate the acoustic pressure and proton speed in different time and different space.The Pennes Heat Transfer Equation was adopted to calculate the temperature distribution through the Finite Difference Time Domain(FDTD)method.Calculate the volume of the region above 60 ? which was considered to be the Treatable Focal Region(TFR),and the volume was compared with the lesion volume obtain from the vitro experiment to verify the correctness of the simulation methods as well as the determination of the TFR.On this basis,a model of liver tumor was established,and the influence of the input intensity,exposure time and the distance between the transducer and the tissue on the TFR was discussed.What's more,the variation of the focal region in tumor during the exposure and cooling period,and the difference to determine the lesion in tumor between temperature threshold and equivalent thermal dose threshold method were explored.Results1.The volume of the lesion volume from bovine liver experiments and the volume of the area above 60 ? from numerical simulation were closed,and the deviation did not exceed 10%.2.In the simulation,when the variation of liver acoustic properties with temperature was considered,under the same input intensity,the time of forming the TFR in tumor was shorter than that in normal liver.When the exposure condition was same,the volume of the TFR in tumor was larger than that in liver.3.In tumor,a given exposure time,the volume of the TFR was increased nonlinearly with the input intensity.4.In tumor,a given input intensity,the volume of the TFR was increased nonlinearly with the exposure time.5.When the volume of the TFR was same,the input intensity and the exposure time is negatively correlated.6.Under different input intensities,when the maximum temperature reached 90 ±1?,the volume of the TFR was reduced with the input intensity increased,and the volume of the TFR in tumor was larger than that in liver.7.Under the same exposure dose,the temperature of the target tissue rise slower and the volume of the TFR grown slower as the distance between the transducer and the tissue was reduced.8.During the exposure period,the TFR length and diameter increased nonlinearly with increasing exposure,but the length increased more quickly.During the cooling period,the length of the TFR almost didn't change while the diameter of the TFR increased a little.9.When the input intensity was ranged from 0.6?1.5 W/cm2,the volume of the TFR determined by the temperature threshold method was smaller than that determined by the equivalent thermal dose threshold method,and the deviation between them was reduced as the input intensity increased.Conclusion1.Verified by experiment,the temperature threshold 60 ? can be used to predict the lesion volume in experiment with an error not exceed 10%.2.Compared with the normal liver,the lesion was formed much easier in tumor.3.When the lesion volume was same,the exposure time and the input intensity was negatively correlated.4.The TFR was influenced by the thickness of the water between the transducer and the tissue.5.After the exposure was stopped,during the cooling period,the shape of the TFR changed a little.6.For the different input intensities,the volume of the TFR determined by the temperature threshold method was smaller than that determined by the equivalent thermal dose threshold method,and the deviation between them was reduced as the input intensity increased.