Numerical Investigation of a Thermal Ablation Porous Media-Based Model for Tumoral Tissue with Variable Porosity

Assunta Andreozzi,Claudio Tucci,Luca Brunese,Giuseppe Peter Vanoli,Marcello Iasiello

doi:10.3390/computation9050050

Assunta Andreozzi, Claudio Tucci + Show 3 more

Open Access

https://doi.org/10.3390/computation9050050

Copy DOI

Abstract

Thermal ablation is a minimally or noninvasive cancer therapy technique that involves fewer complications, shorter hospital stays, and fewer costs. In this paper, a thermal-ablation bioheat model for cancer treatment is numerically investigated, using a porous media-based model. The main objective is to evaluate the effects of a variable blood volume fraction in the tumoral tissue (i.e., the porosity), in order to develop a more realistic model. A modified local thermal nonequilibrium model (LTNE) is implemented including the water content vaporization in the two phases separately and introducing the variable porosity in the domain, described by a quadratic function changing from the core to the rim of the tumoral sphere. The equations are numerically solved employing the finite-element commercial code COMSOL Multiphysics. Results are compared with the results obtained employing two uniform porosity values (ε = 0.07 and ε = 0.23) in terms of coagulation zones at the end of the heating period, maximum temperatures reached in the domain, and temperature fields and they are presented for different blood vessels. The outcomes highlight how important is to predict coagulation zones achieved in thermal ablation accurately. In this way, indeed, incomplete ablation, tumor recurrence, or healthy tissue necrosis can be avoided, and medical protocols and devices can be improved.

Highlights

Thermal ablation is increasingly recognized as an important alternative in cancer treatments, for which the most common procedures applied are surgery, chemotherapy, and radiotherapy
A modified local thermal nonequilibrium model (LTNE) is implemented including the water content vaporization in the two phases separately and introducing the variable porosity in the domain, described by a quadratic function changing from the core to the rim of the tumoral sphere
Pennes developed the first bioheat equation [6], which is still widely used for its simplicity but which reveals critical shortcomings due to the assumptions made, such as the perfusion rate is uniform in the tissue, the blood flow direction, and the artery–vein countercurrent arrangements are neglected, the arterial blood is considered at a constant temperature of about 37 ◦C, while the venous blood is in thermal equilibrium with tissue

Summary

Introduction

Thermal ablation is increasingly recognized as an important alternative in cancer treatments, for which the most common procedures applied are surgery, chemotherapy, and radiotherapy. Nakyama and Kuwahara [18] developed a general set of bioheat transfer equations for blood flows and its surrounding biological tissue employing the volume averaging theory in the field of fluid-saturated porous media. They extended the two-energy equation model to a three-energy equation model in order to include the countercurrent heat transfer between closely spaced arteries and veins in the circulatory system and its effect on the peripheral heat transfer. As for the grid convergence, the effect of different time steps is verified on the maximum temperatures achieved for the lowest porosity and blood velocity, and in Table 4, the results confirm the choice made

Time Step

Findings

Conclusions