Analysis and analytical characterization of bioheat transfer during radiofrequency ablation

Transarterial Chemoembolization Plus Radiofrequency Ablation and Iodine-125 Seed Implantation for Hepatocellular Carcinoma in High-Risk Locations: A Propensity Score-Matched Analysis

Background & Aims

The effect of transarterial chemoembolization (TACE) plus radiofrequency ablation (RFA) (TACE-RFA) for hepatocellular carcinoma (HCC) in high-risk locations is not satisfactory. The aim of this study was to compare the clinical outcomes of TACE-RFA plus iodine-125 (125I) seed implantation (TACE-RFA-125I) therapy with those of TACE-RFA for unresectable HCC (≤5 cm) in high-risk locations.

Methods

From January 2010 to June 2023, the clinical data of 126 patients with unresectable HCC (≤5 cm) in high-risk locations who received TACE-RFA-125I or TACE-RFA treatment were retrospectively analyzed. The clinical outcomes between the two groups were compared after propensity score matching (PSM) analysis.

Results

Forty-six pairs of patients were matched. The local progression-free survival rates at 1-, 2-, 3-, 4-, and 5-years were 100%, 82.4%, 74.8%, 63.5%, and 54% in the TACE-RFA-125I group, which were significantly higher than 91.3%, 69.4%, 50.7%, 29.4%, and 26.7% in the TACE-RFA group, respectively (p = 0.004). The median progression-free survival in the TACE-RFA-125I group was significantly longer than that in the TACE-RFA group (p = 0.002). The overall survival rates at 1-, 2-, 3-, 4-, and 5-years were 100%, 93.4%, 80.7%, 74.9%, and 64.7% in the TACE-RFA-125I group, which were significantly higher than 97.8%, 78%, 68.6%, 51.1%, and 45.3% in the TACE-RFA group, respectively (p = 0.011). There was no occurrence of major complications or procedure-related deaths in the two groups.

Conclusion

Compared with the TACE-RFA treatment, TACE-RFA-125I should be a more effective treatment strategy for patients with unresectable HCC (≤5 cm) in high-risk locations.

Enhancing the therapeutic impact of sublethal radiofrequency hyperthermia in malignant solid tumor treatment

Radiofrequency ablation (RFA) is an effective alternative to surgery for managing some malignant solid tumors. However, for medium-to-large tumors (>3 cm), tumors adjacent to large blood vessels, and certain irregular tumors, sublethal radiofrequency hyperthermia (RFH) often produces a margin of ablated tumor owing to the "heat-sink" effect. This effect typically leaves behind viable residual tumors at the margin. Several studies have reported that a sublethal RFH can significantly enhance the efficacy of chemotherapy, radiotherapy, immunotherapy, and gene therapy for malignant solid tumors. The possible mechanisms by which RFH enhances these therapies include heat-induced tissue fracturing, increased permeability of the cytoplasmic membrane, exaggerated cellular metabolism, blockade of the repair pathways of radiation-damaged tumor cells, and activation of the heat shock protein pathways. Therefore, RFA in combination with chemotherapy, radiotherapy, immunotherapy, or gene therapy may help reduce the rates of residual and recurrent tumors after RFA of malignant solid tumors.

Microwave ablation modeling with AMICA antenna: Validation by means a numerical analysis

BACKGROUND AND OBJECTIVES

Percutaneous microwave thermal ablation is based on electromagnetic waves that generate dielectric heating, and it is widely recognized as one of the mostly used techniques for tumor treatment. The aim of this work is to validate a predictive model capable of providing physicians with guidelines to be used during thermal ablation procedures avoiding collateral damage.

METHODS

A finite element commercial software, COMSOL Multiphysics, is employed to implement a tuning-parameter approach. Governing equations are written with reference to variable-porosity and Local Thermal Non-Equilibrium (LTNE) equations are employed. The simulations results are compared with available ex-vivo and in-vivo data with the help of regression analysis. For in-vivo data simulations, velocity vector modulus and direction are varied between 0.0007 and 0.0009 m/s and 90-270°, respectively, in order to use this parameter as a tuning one to simulate - and lately optimize with respect to the differences from experimental outcomes - all the possible directions of the blood flow with respect to the antenna, whose insertion angle is not registered in the dataset.

RESULTS

The model is validated using reference data provided by the manufacturer (AMICA), which is obtained from ex-vivo bovine liver. The model accurately predicts the size and shape of the ablated area, resulting in an overestimation lesser than 10 %. Additionally, predictive data are compared to an in-vivo dataset. The ablated volume is accurately predicted with a mean underestimation of 6 %. The sphericity index is calculated as 0.75 and 0.62 for the predictions and in-vivo data, respectively.

CONCLUSION

This study developed a predictive model for microwave ablation of liver tumors that showed good performance in predicting ablation dimensions and sphericity index for ex-vivo bovine liver and for in-vivo human liver data with the tuning technique. The study emphasizes the necessity for additional development and validation to enhance the accuracy and reliability of in-vivo application.

Effects of Pulsed Radiofrequency Source on Cardiac Ablation

Heart arrhythmia is caused by abnormal electrical conduction through the myocardium, which in some cases, can be treated with heat. One of the challenges is to reduce temperature peaks-by still guaranteeing an efficient treatment where desired-to avoid any healthy tissue damage or any electrical issues within the device employed. A solution might be employing pulsed heat, in which thermal dose is given to the tissue with a variation in time. In this work, pulsed heat is used to modulate induced temperature fields during radiofrequency cardiac ablation. A three-dimensional model of the myocardium, catheter and blood flow is developed. Porous media, heat conduction and Navier-Stokes equations are, respectively, employed for each of the investigated domains. For the electric field, solved via Laplace equation, it is assumed that the electrode is at a fixed voltage. Pulsed heating effects are considered with a cosine time-variable pulsed function for the fixed voltage by constraining the product between this variable and time. Different dimensionless frequencies are considered and applied for different blood flow velocity and sustained voltages. Results are presented for different pulsed conditions to establish if a reasonable ablation zone, known from the obtained temperature profiles, can be obtained without any undesired temperature peaks.

Mathematical modeling of microwave liver ablation with a variable-porosity medium approach

BACKGROUND AND OBJECTIVES

Thermal ablation of tumors plays a key role to fight cancer, since it is a minimally invasive treatment which involves some advantages compared to surgery and chemotherapy, such as shorter hospital stays and consequently lower costs, along with minor side effects. In this context, computational modeling of heat transfer during thermal ablation is relevant to accurately predict the obtained ablation zone in order to avoid tumor recurrence risk caused by incomplete ablation, and the same time to save the surrounding healthy tissue. The aim of this work is to develop a more realistic porous media-based mathematical model to simulate a microwave thermal ablation (MWA) of an in vivo liver tumor surrounded by healthy tissue.

METHODS

The domain is made up of a spherical tumor bounded by a cylindrical healthy liver tissue. The simulated microwave antenna is a 14 G HS Amica-Gen Probe, and the supplied power of 60 W is applied for 300 s and 600 s. The model consists in coupling modified Local Thermal Non Equilibrium (LTNE) equations with the electromagnetic equations. The LTNE equations include a variable porosity function which fits the porosity changing from the tumor core to the rim based on experimental measures in in vivo cases. Moreover, four different blood vessels' uniform distributions are investigated to compare the effects of different vascularizations of the considered target tissue.

RESULTS

The results are shown in terms of temperature fields, ablation diameters and volumes based on the Arrhenius thermal damage model with 99% of cell death probability. The outcomes show a very good agreement with a clinical study on human patients with hepatocellular carcinoma using the same antenna and energy setting, when terminal arteries distribution is included.

CONCLUSIONS

In this work, an in vivo microwave ablation of liver tumor surrounded by healthy tissue is modeled with a variable-porosity medium approach based on experimental measures. The outcomes shown for distinct vascularizations underline the key relevance of modeling more and more accurately tumor MWA, by considering increasingly realistic features, avoiding tumor recurrence, and improving both medical protocols and devices.

Numerical analysis of the pulsating heat source effects in a tumor tissue

BACKGROUND AND OBJECTIVES

Hyperthermia treatment is nowadays recognized as the fourth additional cancer therapy technique following surgery, chemotherapy, and radiation; it is a minimally or non-invasive technique which involves fewer complications, a shorter hospital stay, and fewer costs. In this paper, pulsating heat effects on heat transfer in a tumor tissue under hyperthermia are analyzed. The objective of the paper is to find and quantify the advantages of pulsatile heat protocols under different periodical heating schemes and for different tissue morphologies.

METHODS

The tumor tissue is modeled as a porous sphere made up of a solid phase (tissue, interstitial space, etc.) and a fluid phase (blood). A Local Thermal Non-Equilibrium (LTNE) model is employed to consider the local temperature difference between the two phases. Governing equations with the appropriate boundary conditions are solved with the finite-element code COMSOL Multiphysics®. The pulsating effect is modeled with references to a cosine function with different frequencies, and such different heating protocols are compared at equal delivered energy, i. e. different heating times at equal maximum power.

RESULTS

Different tissue properties in terms of blood vessels sizes and blood volume fraction in tissue (porosity) are investigated. The results are shown in terms of tissue temperature and percentage of necrotic tissue obtained. The most powerful result achieved using a pulsating heat source instead of a constant one is the decreasing of maximum temperature in any considered case, even reaching about 30% lower maximum temperatures. Furthermore, the evaluation of tissue damage at the end of treatment shows that pulsating heat allows to necrotize the same tumoral tissue area of the non-pulsating heat source.

CONCLUSIONS

Modeling pulsating heat protocols in thermal ablation under different periodical heating schemes and considering different tissues morphologies in a tumor tissue highlights how the application of pulsating heat sources allows to avoid high temperature peaks, and simultaneously to ablate the same tumoral area obtained with a non-pulsating heat source. This is a powerful result to improve medical protocols and devices in thermal ablation of tumors.

A Study on Non-Linear DPL Model for Describing Heat Transfer in Skin Tissue during Hyperthermia Treatment

The article studies the simulation-based mathematical modeling of bioheat transfer under the Dirichlet boundary condition. We used complex non-linear dual-phase-lag bioheat transfer (DPLBHT) for analyzing the temperature distribution in skin tissues during hyperthermia treatment of infected cells. The perfusion term, metabolic heat source, and external heat source were the three parts of the volumetric heat source that were used in the model. The non-linear DPLBHT model predicted a more accurate temperature within skin tissues. The finite element Runge–Kutta (4,5) (FERK (4,5)) method, which was based on two techniques, finite difference and Runge–Kutta (4,5), was applied for calculating the result in the case of our typical non-linear problem. The paper studies and presents the non-dimensional unit. Thermal damage of normal tissue was observed near zero during hyperthermia treatment. The effects of the non-dimensional time, non-dimensional space coordinate, location parameter, regional parameter, relaxation and thermalization time, metabolic heat source, associated metabolic heat source parameter, perfusion rate, associated perfusion heat source parameter, and external heat source coefficient on the dimensionless temperature profile were studied in detail during the hyperthermia treatment process.

Thermal ablation of biological tissues in disease treatment: A review of computational models and future directions

Percutaneous thermal ablation has proven to be an effective modality for treating both benign and malignant tumours in various tissues. Among these modalities, radiofrequency ablation (RFA) is the most promising and widely adopted approach that has been extensively studied in the past decades. Microwave ablation (MWA) is a newly emerging modality that is gaining rapid momentum due to its capability of inducing rapid heating and attaining larger ablation volumes, and its lesser susceptibility to the heat sink effects as compared to RFA. Although the goal of both these therapies is to attain cell death in the target tissue by virtue of heating above 50°C, their underlying mechanism of action and principles greatly differs. Computational modelling is a powerful tool for studying the effect of electromagnetic interactions within the biological tissues and predicting the treatment outcomes during thermal ablative therapies. Such a priori estimation can assist the clinical practitioners during treatment planning with the goal of attaining successful tumour destruction and preservation of the surrounding healthy tissue and critical structures. This review provides current state-of-the-art developments and associated challenges in the computational modelling of thermal ablative techniques, viz., RFA and MWA, as well as touch upon several promising avenues in the modelling of laser ablation, nanoparticles assisted magnetic hyperthermia and non-invasive RFA. The application of RFA in pain relief has been extensively reviewed from modelling point of view. Additionally, future directions have also been provided to improve these models for their successful translation and integration into the hospital work flow.

Numerical Analysis of Human Cancer Therapy Using Microwave Ablation

Microwave ablation is one type of hyperthermia treatment of cancer that involves heating tumor cells. This technique uses electromagnetic wave effects to kill cancer cells. A micro-coaxial antenna is introduced into the biological tissue. The radiation emitted by the antenna is absorbed by the tissue and leads to the heating of cancer cells. The diffuse increase in temperature should reach a certain value to achieve the treatment of cancer cells but it should be less than a certain other value to avoid damaging normal cells. This is why hyperthermia treatment should be carefully monitored. A numerical simulation is useful and may provide valuable information. The bio-heat equation and Maxwell’s equations are solved using the finite element method. Electro-thermal effects, temperature distribution profile, specific absorption rate (SAR), and fraction of necrotic tissue within cancer cells are analyzed. The results show that SAR and temperature distribution are strongly affected by input microwave power. High microwave power causes a high SAR value and raises the temperature above 50 °C, which may destroy healthy cells. It is revealed that with a power of 10 W, the tumor cells will be killed without damaging the surrounding tissue.

Numerical study on the effects of blood perfusion and body metabolism on the temperature profile of human forearm in hyperthermia conditions

The development of mathematical models for describing the thermal behavior of living tissues under normal or hyperthermia conditions is of increasing importance. In this research, a 3D forearm model based on anthropometric measurement of 25 samples in Tehran, Iran was developed. The tissue temperature distribution is obtained via the Finite Volume Method (FVM) by considering the appropriate boundary conditions, blood perfusion, body metabolism, and the application of hyperthermia conditions on the tissue. The Pennes Bioheat Transfer Equation (PBHTE) is considered in this regard. Also, various thermophysical properties are assumed for the model in order to clarify the effects of such parameters on the tissue temperature distribution. The results of this study indicate that it is possible to provide the desired conditions for many therapeutic processes by controlling the parameters such as blood perfusion, body metabolism and the type of external heat source applied on the tissue. Generally, by decreasing the body metabolism, increasing the blood perfusion rate in tissue and applying a fluctuating heat flux, instead of uniform heat flux on the surface of the forearm skin, it is possible to provide the hyperthermia conditions without causing damages such as burn injuries to the other parts of the tissue. By using the results of this study, the appropriate conditions of hyperthermia can be obtained.

Imaging finding and arthroscopic treatment of isolated contracture of the rectus femoris muscle: a case report

Background

Isolated rectus femoris (RF) contracture is encountered very rarely in orthopaedic practices. There are few reports on its imaging manifestations and no cases reported to be treated with arthroscopy.

Case presentation

A 11-year-old girl with a more than 7 years history of restricted left knee flexion was presented. The clinical assessment and magnetic resonance imaging (MRI) findings were detailed here. A strip-like induration was palpated in the left thigh, which tends to be more obvious with knee flexion. MRI demonstrated a hypointensity band connected the anterior inferior iliac spine with the patella, and marked atrophy of the left RF muscle. Fibrosis contracture band was confirmed with arthroscope, then divided by radiofrequency ablation (RFA) under arthroscopic observation. Followed by debridement of the fibrillar connective tissue and hemostasis around the broken ends. The movement of left knee joint significantly improved after the operation, and the patient recovered nearly full range of motion of this joint after 6 months.

Conclusion

The specific MRI findings could assist in confirming clinical early diagnosis of isolated RF contracture. Arthroscopic RFA treatment is an effective technique to treat this disorder with minimally incision.

Electronic supplementary material

The online version of this article (10.1186/s12891-019-2696-8) contains supplementary material, which is available to authorized users.

Modeling Heat Transfer in Tumors: A Review of Thermal Therapies

It is quite challenging to describe heat transfer phenomena in living systems because of the involved phenomena complexity. Indeed, thermal conduction and convection in tissues, blood perfusion, heat generation due to metabolism, complex vascular structure, changing of tissue properties depending on various conditions, are some of the features that make hard to obtain an accurate knowledge of heat transfer in living systems for all the clinical situations. This theme has a key role to predict accurately the temperature distribution in tissues, especially during biomedical applications, such as hyperthermia treatment of cancer, in which tumoral cells have to be destroyed and at the same time the surrounding healthy tissue has to be preserved. Moreover, the lack of experimentation in this field, due to ethical reasons, makes bioheat models even more significant. The first simple bioheat model was developed in 1948 by Pennes (J Appl Physiol 1:93-122, 1948) but it has some shortcomings that make the equation not so accurate. For this reason, over the years it has been modified and more complex models have been developed. The purpose of this review is to give a clear overview of how the bioheat models have been modified when applied in various hyperthermia treatments of cancer.

ANALYTICAL SOLUTION OF HYPERBOLIC BIOHEAT EQUATION IN SPHERICAL COORDINATES APPLIED IN RADIOFREQUENCY HEATING

This paper presents an analytical solution for the hyperbolic bioheat equation in spherical coordinates under nonuniform distributed heat source term, which is theoretically modeling the Radiofrequency Heating (RFH) technique. In RFH technique a spherical electrode is inserted into the diseased tissue which leads to the heat generation there due to the imposed electromagnetic field. Because of the non-Fourier behavior of biological tissues, the hyperbolic Penne’s equation is adopted as perfused thermal model. The equation has been solved using Eigenvalue method and the closed form solutions are introduced. The temperature profiles are determined for a sample RFH procedure in cornea and liver and the effect of perfusion term in Penne’s bioheat equation is shown. The effective parameters in the RFH process such as electrode radius, power and different material are studied analytically too. The derived solution can play a role of verification basis of other numerical ones in this area.

Validation of Numerically Simulated Tissue Temperatures During Transcutaneous Recharge of Neurostimulation Systems

OBJECTIVE

A research study combining numerical simulation and animal-model experiments has been performed to assess the ability of simulation to accurately calculate temperatures within living tissue during the recharge of a neuromodulation system (Restore Ultra device, Medtronic Neuromodulation, Minneapolis, MN, USA).

MATERIALS AND METHODS

The experiments were carried out on a sheep with the neuromodulation implant set to depths of 0.6 cm and 2.1 cm. Temperatures were recorded on the surfaces of the implant and on the sheep skin. Finite element simulations were carried out to determine the degree to which the simulations and experiments match. Additional calculations were performed for an intermediate implant depth.

RESULTS

It was found that there was excellent agreement between the simulations and the animal model for both depths.

CONCLUSION

It is shown that numerical simulation using the Pennes bioheat equation is capable of predicting temperature increases within living tissues when implanted heat-generating devices are in use. The device used in the present study does not give rise to temperatures which cause concern of thermal injury or safety. The study was performed for aligned antenna and implant.

Estimating the time and temperature relationship for causation of deep-partial thickness skin burns

The objective of this study is to develop and present a simple procedure for evaluating the temperature and exposure-time conditions that lead to causation of a deep-partial thickness burn and the effect that the immediate post-burn thermal environment can have on the process. A computational model has been designed and applied to predict the time required for skin burns to reach a deep-partial thickness level of injury. The model includes multiple tissue layers including the epidermis, dermis, hypodermis, and subcutaneous tissue. Simulated exposure temperatures ranged from 62.8 to 87.8°C (145-190°F). Two scenarios were investigated. The first and worst case scenario was a direct exposure to water (characterized by a large convection coefficient) with the clothing left on the skin following the exposure. A second case consisted of a scald insult followed immediately by the skin being washed with cool water (20°C). For both cases, an Arrhenius injury model was applied whereby the extent and depth of injury were calculated and compared for the different post-burn treatments. In addition, injury values were compared with experiment data from the literature to assess verification of the numerical methodology. It was found that the clinical observations of injury extent agreed with the calculated values. Furthermore, inundation with cool water decreased skin temperatures more quickly than the clothing insulating case and led to a modest decrease in the burn extent.