Numerical Simulation Of HIFU Therapeutic Dose For Liver Tumors

As a non-invasive or minimally invasive cancer therapeutic technology,High intensity focused ultrasound,has been applied to the clinical treatment of various solid tumors.However,due to many unsolved problems,such as the non-invasive real-time monitoring and therapeutic dose,residual tumor tissue or over-treatment will occur in the clinical treatment process,which can lead the security and reliability not to be guaranteed.ObjectiveResearch on the HIFU therapeutic dose for liver tumors by numerical simulation method,and then discuss the temperature field on different input therapeutic dose,and the affects of tissue acoustic properties and focus depth on the location,size,shape of treatment target.The results can provide the theory reference data and theoretical basis for clinical HIFU therapeutic dose formulation.MethodsIn this study,a model of excised porcine liver was established,with the approximation of Westervelt Formula for the nonlinear propagation of ultrasound,proposed by Nagayoshi Moritato,and the Pennes Heat Transfer Equation,we simulated the temperature elevation,pressure and the proton speed of the nonlinear propagation of ultrasound at different time and space using FDTD method.Based on the comparison between temperature threshold and the equivalent thermal dose threshold method,we established the quantitative method of HIFU therapeutic region used in this study.Using this method,we analyzed and discussed the influence of tissue acoustic properties on HIFU temperature field.and then we discussed the HIFU therapeutic region on different therapeutic dose with considering the influence of tissue acoustic properties,and compared the simulation and experimental results preliminarily.Results1.Equivalent thermal dose distribution is relatively more concentrated on focal point than the temperature rise curve in the acoustic axis;The rise rate of the equivalent thermal dose is higher than the temperature rise rate;The size of therapeutic focus is different by using different temperature thresholds and equivalent thermal dose threshold,the difference among the temperature thresholds is larger,and the equivalent thermal dose thresholds is relatively small.2.When the input intensity and exposure time arel.0W/cm2and 5s,respectively,focus temperature is 4.81? higher with considering the tissue acoustic properties than without considering them,but the length of therapeutic region is 0.3mm smaller;The longer the exposure time,the more obvious influence of tissue acoustic properties.3.For a given exposure time,the therapeutic region length and diameter increases in a nonlinear form with increasing input intensity,and the change of therapeutic region length is apparent.4.Therapeutic region length and diameter increases also in a nonlinear form with increasing exposure time on a given input intensity.5.The deeper the focus depth,the farther the distance between actual focus and geometric focus,the lower the peak temperature elevation,and the shorter both therapeutic region length and diameter,the change of therapeutic region length is larger than the diameter.6.Under a given focus depth and the equal therapeutic region length conditions,The higher input intensity requires less time,the lower input intensity requires more time,input intensity and exposure time is negatively correlated,At the same time,the change of therapeutic region diameter is small.7.Under the same input condition,the difference between the lesion region length and diameter of experiment and simulation is small;The lesion region area of simulation is slightly larger than experiment;The theoretical prediction is in good agreement with the experimental results of single exposure.Conclusions1.Equivalent thermal dose distribution is relatively more concentrated than the temperature rise curve in the acoustic axis;The rise rate of the equivalent thermal dose is higher than the temperature rise rate;The size of therapeutic focus is different by using different temperature thresholds and equivalent thermal dose threshold.2.The influence of tissue acoustic properties should not be ignored,especially for long exposure time.3.The therapeutic region length and diameter increases in a nonlinear form with increasing input intensity on a given exposure time;.4.For a given input intensity,therapeutic region length and diameter increases also in a nonlinear form with increasing exposure time;5.With increasing to the focus depth,both therapeutic region length and diameter get shorter.6.When the therapeutic region length are equal,input intensity and exposure time is negatively correlated.