Hyperthermia Therapy of a Biological Tissue CFD Simulation
One of the most effective methods in the treatment of cancer is the use of hyperthermia therapy, whereby the temperature is greatly increased by the application of ultrasound to the cancer tissue center.
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Problem Description for Hyperthermia Therapy
Common methods of cancer treatment include surgery, radiotherapy, and chemotherapy. These methods have disadvantages including aggressiveness, irreversibility, and side effects. Warming in Hyperthermia Therapy prevents oxygen and nutrients from getting into the unhealthy tissue; in this way, proteins within the tissue change nature and can surround the cancer cells. This makes it possible for the immune system to identify cancer cells.
The present study examined blood flow in capillaries passing through a tissue containing cancerous tumors and using Hyperthermia Therapy. For this purpose, we assume a spherical space to be an example of a healthy body tissue or cell in which blood flows at a very slow rate. There are several veins within this tissue. The vein structure of cells and tissues of the body are like bushes. To simplify the problem, we assumed that all the veins, align uniformly in the tissue (X axis). As the blood flow passes through the spaces within the tissue, the whole tissue can be considered a porous medium.
There are four spherical cancerous tumors of different diameters at the center of this tissue and on the surface of the veins as Biological Tissue. In fact, the thermophysical properties of a healthy tissue differ from those of cancer cells, but to simplify this, we assume the thermophysical properties of the healthy tissue similar to the unhealthy cells. Every cancerous tissue is a heat source with heat energy per unit of volume to cause heat transfer and thereby significantly increase blood flow. The purpose of this study is to investigate the response of blood vessels and body tissues to this heat.
The Assumption for Biological Tissue Hyperthermia Therapy
Hyperthermia Therapy CFD Simulation of the problem is transient (unsteady).
We use a pressure-based solver for the simulation.
We do not consider the effect of the earth’s gravity on the blood flow.
Geometry & Mesh
Design Modeler software, design the 3-D model of Biological Tissue. The present model comprises a cylindrical tube as the capillary, four spherical blood vessels attached to the capillary as tumors, and a spherical space for intra-arterial blood flow around the vein, which has a slower flow rate than flow Inside the capillaries. Spherical tissues around the capillary have a different radius (3, 5, 6, and 7.5 mm). The outer sphere is also considered as the space for blood flow within the tissue and around the capillary, which contains two input and output hemispheres. Meshing was performed by ANSYS Meshing software. The present grid was unstructured with 717087 cells.
Hyperthermia Therapy CFD Simulation Steps:
Here is a summary of the steps to define and solve the problem in the table:
|Standard wall function|
|(boundary conditions) Hyperthermia Therapy|
|inlet blood to the capillary||velocity||0.08 m.s-1|
|inlet blood around the capillary||velocity||0.000035 m.s-1|
|outlet blood from the capillary||pressure||0 Pa|
|outlet blood around the capillary||pressure||0 Pa|
|(Methods) Hyperthermia Therapy|
|discretization||momentum||Second order upwind|
|pressure||Second order upwind|
|energy||Second order upwind|
|kinetic||First order upwind|
|dissipation||First order upwind|
|(initialization) Hyperthermia Therapy|
Source Term for Hyperthermia Therapy
According to the problem description, each of the four spherical cancer tissues is subjected to heat by ultrasonic waves. The amount of heating per unit of the volume of the tissues is given within ten seconds. Therefore, the Source Term option is used. The UDF code is used to define the amount of heat applied per volume unit. In fact, the heat generation at the center point of each sphere is about 10,000,000 W.m-3, while at the other parts of the sphere at a certain distance from the center, it is less than the defined heat. So a UDF code will be needed to define the amount of heat per unit volume of spheres volume.
In this simulation, we need to define two substances: blood (fluid) and tissue (solid). Since these materials have their own thermophysical properties, they are defined manually with available properties. The thermophysical properties of blood and tissue are listed in the following table:
|tissue (solid)||Blood (fluid)|
|Specific heat (j.kg-1.K-1)||3770||3770|
|Thermal conductivity (W.m-1.K-1)||0.5||0.5|
As the blood flows through the capillaries through the empty cavities within the tissues, the tissue is defined as a porous medium. The value of the porosity coefficient is equal to the ratio of the volume of vacant space to the total space volume, which is considered to be 0.05.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.
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