Study Of The Needle Targeting Error Analysis And Mechanics Modeling In Prostate Brachytherapy

Percutaneous needle insertion is becoming more popular in minimally invasive surgery treatment. Prostate brachytherapy is one typical percutaneous needle insertion process in which needles are inserted into the human tissue towards a specified target. In this paper, we are committed to the calculation of the needle targeting error by providing a comprehensive study on both modeling and simulation of the needle-tissue interaction process. Dose values before and after error compensation proves the method have obvious effects. The solution can also be used in optimizing trajectory of the needle tip, enabling the needle to reach the target without touching important physiological structures such as blood vessels with the help of dynamic trajectory planning.First, needle insertion force model and a mechanics-based needle deflection model are applied in simulating the real needle insertion process. Based on the principle of minimum potential energy, a mechanics-based model is developed to calculate needle deflection. The needle deflection model incorporates needle insertion forces model, needle-tissue interaction model, needle geometric and tissue properties.Second, a 2D-planar FE model is used to model the target displacement by imposing needle distribution forces and needle deflection at different steps on the appointed reference nodes. The soft tissue is modeled as a nonlinear hyperelastic material with geometrical nonlinearity. Then Magnetic resonance images(MRI) are used to reconstruct the prostate, establishing both prostate 3D finite element(FE) model and artificial prostate model. The needle-soft tissue interaction simulation results are compared with the needle insertion experiment. Needle targeting experiments are conducted to validate the simulation results. Besides, we conduct different experiments to compensate the obtained targeting error and obtain preferable effects.At last, the pelvis solid model is used to perform needle insertion force and tissue deformation experiments. The flexible needle is inserted into human pelvis at perineum. The insertion situation can be expressed by the force profile. Besides, the pelvis model insertion force profile is compared with the simple insertion process. CCD camera is used to observe the prostate deformation and ultrasonic probe are used to observe the overall deformation in one cross-section. The results and products of this paper can be used in improving the accuracy of trajectory planning and needle insertion.