A review of radiofrequency ablation: Large target tissue necrosis and mathematical modelling

Computer simulation-based nanothermal field and tissue damage analysis for cardiac tumor ablation

Radiofrequency ablation is a nominally invasive technique to eradicate cancerous or non-cancerous cells by heating. However, it is still hampered to acquire a successful cell destruction process due to inappropriate RF intensities that will not entirely obliterate tumorous tissues, causing in treatment failure. In this study, we are acquainted with a nanoassisted RF ablation procedure of cardiac tumor to provide better outcomes for long-term survival rate without any recurrences. A three-dimensional thermo-electric energy model is employed to investigate nanothermal field and ablation efficiency into the left atrium tumor. The cell death model is adopted to quantify the degree of tissue injury while injecting the Fe3O4 nanoparticles concentrations up to 20% into the target tissue. The results reveal that when nanothermal field extents as a function of tissue depth (10 mm) from the electrode tip, the increasing thermal rates were approximately 0.54362%, 3.17039%, and 7.27397% for the particle concentration levels of 7%, 10%, and 15% compared with no-particle case. In the 7% Fe3O4 nanoparticles, 100% fractional damage index is achieved after ablation time of 18 s whereas tissue annihilation approach proceeds longer to complete for no-particle case. The outcomes indicate that injecting nanoparticles may lessen ablation time in surgeries and prevent damage to adjacent healthy tissue.

Non-Fourier Bioheat Transfer Analysis in Brain Tissue During Interstitial Laser Ablation: Analysis of Multiple Influential Factors

This work presents the dual-phase lag-based non-Fourier bioheat transfer model of brain tissue subjected to interstitial laser ablation. The finite element method has been utilized to predict the brain tissue's temperature distributions and ablation volumes. A sensitivity analysis has been conducted to quantify the effect of variations in the input laser power, treatment time, laser fiber diameter, laser wavelength, and non-Fourier phase lags. Notably, in this work, the temperature-dependent thermal properties of brain tissue have been considered. The developed model has been validated by comparing the temperature obtained from the numerical and ex vivo brain tissue during interstitial laser ablation. The ex vivo brain model has been further extended to in vivo settings by incorporating the blood perfusion effects. The results of the systematic analysis highlight the importance of considering temperature-dependent thermal properties of the brain tissue, non-Fourier behavior, and microvascular perfusion effects in the computational models for accurate predictions of the treatment outcomes during interstitial laser ablation, thereby minimizing the damage to surrounding healthy tissue. The developed model and parametric analysis reported in this study would assist in a more accurate and precise prediction of the temperature distribution, thus allowing to optimize the thermal dosage during laser therapy in the brain.

Optimal design of aperiodic tri-slot antennas for the conformal ablation of liver tumors using an experimentally validated MWA computer model

OBJECTIVE

This study aims to demonstrate that the conformal microwave ablation (MWA) of liver tumors could be attained by optimizing the structure of an aperiodic tri-slot coaxial antenna, its insertion depth, and input power.

METHODS

A computational MWA model with an aperiodic tri-slot coaxial antenna operating at the frequency of 2.45 GHz was built and validated by both an ex vivo and a pilot in vivo experiment with porcine healthy livers. The validated in vivo computational MWA model implemented with a liver tumor was then used as a testbed to investigate the conformal ablation of liver tumors. Five liver tumors in different sizes and shapes were investigated. A genetic algorithm optimization method (NSGA-II) was used to optimize the structure of antenna, insertion depth of antenna, and microwave antenna input power for the conformal ablation of liver tumors.

RESULTS

The validation results showed that a good agreement in both the spatiotemporal temperature distribution and ablation zone was found between the computer model and the ex vivo experiments at both 45 W, 5 min and 60 W, 3 min treatments and the in vivo experiment at 45 W, 5 min treatment. The optimized simulation results confirmed that five cases of liver tumors in different sizes and shapes can be conformally ablated by optimizing the aperiodic tri-slot coaxial antenna, antenna insertion depth, and microwave antenna input power.

CONCLUSION

This paper demonstrates that the aperiodic tri-slot coaxial antenna can be optimized with the insertion depth and input power for the conformal ablation of liver tumors, regardless the size and shape of liver tumors.

Model-Optimizing Radiofrequency Parameters of 3D Finite Element Analysis for Ablation of Benign Thyroid Nodules

Radiofrequency (RF) ablation represents an efficient strategy to reduce the volume of thyroid nodules. In this study, a finite element model was developed with the aim of optimizing RF parameters, e.g., input power and treatment duration, in order to achieve the target volume reduction rate (VRR) for a thyroid nodule. RF ablation is modelled as a coupled electro-thermal problem wherein the electric field is applied to induce tissue heating. The electric problem is solved with the Laplace equation, the temperature distribution is estimated with the Pennes bioheat equation, and the thermal damage is evaluated using the Arrhenius equation. The optimization model is applied to RF electrode with different active tip lengths in the interval from 5 mm to 40 mm at the 5 mm step. For each case, we also explored the influence of tumour blood perfusion rate on RF ablation outcomes. The model highlights that longer active tips are more efficient as they require lesser power and shorter treatment time to reach the target VRR. Moreover, this condition is characterized by a reduced transversal ablation zone. In addition, a higher blood perfusion increases the heat dispersion, requiring a different combination of RF power and time treatment to achieve the target VRR. The model may contribute to an improvement in patient-specific RF ablation treatment.

Simulating radiofrequency ablation of hepatocellular carcinomas proximal to bare area of liver

PURPOSE

To numerically assess the significance of dextrose 5% in water (D5W) thermo-protection during radiofrequency ablation (RFA) of hepatocellular carcinomas (HCCs) located near the 'bare area of liver'.

MATERIAL AND METHODS

This study utilises quasi-anatomical structures extracted from CT images. A multi-tine electrode, deployed inside the extracted organs and operated under temperature-controlled mode was used as the source of ablation. Geometrically, D5W was modelled around the 'bare area' and sandwiched between the liver and diaphragm. RFA at different sites relative to the 'bare area' was simulated to answer when to consider modelling D5W.

RESULTS

For targets near the edge of 'bare area' and at 0.5 mm gap (between the electrode and the 'bare area'), ignoring D5W and using ground conditions could result in underestimation of ablation volume by almost 25%. The importance of D5W becomes negligible for ablations near the centre of the 'bare area'.

CONCLUSIONS

Consideration of D5W during RFA of HCCs proximal to the 'bare area' can significantly influence the ablation outcome, especially when ablation is performed near the edge of the 'bare area'.

Long-term outcomes of radiofrequency ablation vs. partial nephrectomy for cT1 renal cancer: A meta-analysis and systematic review

Background

Partial nephrectomy (PN) is one of the most preferred nephron-sparing treatments for clinical T1 (cT1) renal cancer, while radiofrequency ablation (RFA) is usually used for patients who are poor surgical candidates. The long-term oncologic outcome of RFA vs. PN for cT1 renal cancer remains undetermined. This meta-analysis aims to compare the treatment efficacy and safety of RFA and PN for patients with cT1 renal cancer with long-term follow-up of at least 5 years.

Method

This meta-analysis was performed following the PRISMA reporting guidelines. Literature studies that had data on the comparison of the efficacy or safety of RFA vs. PN in treating cT1 renal cancer were searched in databases including PubMed, Embase, Web of Science, and the Cochrane Library from 1 January2000 to 1 May 2022. Only long-term studies with a median or mean follow-up of at least 5 years were included. The following measures of effect were pooled: odds ratio (OR) for recurrence and major complications; hazard ratio (HR) for progression-free survival (PFS), cancer-specific survival (CSS), and overall survival (OS). Additional analyses, including sensitivity analysis, subgroup analysis, and publication bias analysis, were also performed.

Results

A total of seven studies with 1,635 patients were finally included. The treatment efficacy of RFA was not different with PN in terms of cancer recurrence (OR = 1.22, 95% CI, 0.45-3.28), PFS (HR = 1.26, 95% CI, 0.75-2.11), and CSS (HR = 1.27, 95% CI, 0.41-3.95) as well as major complications (OR = 1.31, 95% CI, 0.55-3.14) (P > 0.05 for all). RFA was a potential significant risk factor for OS (HR = 1.76, 95% CI, 1.32-2.34, P < 0.001). No significant heterogeneity and publication bias were observed.

Conclusion

This is the first meta-analysis that focuses on the long-term oncological outcomes of cT1 renal cancer, and the results suggest that RFA has comparable therapeutic efficacy with PN. RFA is a nephron-sparing technique with favorable oncologic efficacy and safety and a good treatment alternative for cT1 renal cancer.

Thermal ablation effects on rotors that characterize functional re-entry cardiac arrhythmia

Thermal ablation is a well-established successful treatment for cardiac arrhythmia, but it still presents limitations that require further studies and developments. In the rotor-driven functional re-entry arrhythmia, tissue heterogeneity results on the generation of spiral/scroll waves and wave break dynamics that may cause dangerous sustainable fibrillation. The selection of the target region to perform thermal ablation to mitigate this type of arrhythmia is challenging, since it considerably affects the local electrophysiology dynamics. This work deals with the numerical simulation of the thermal ablation of a cardiac muscle tissue and its effects on the dynamics of rotor-driven functional re-entry arrhythmia. A non-homogeneous two-dimensional rectangular region is used in the present numerical analysis, where radiofrequency ablation is performed. The electrophysiology problem for the propagation of the action potential in the cardiac tissue is simulated with the Fenton-Karma model. Thermal damage caused to the tissue by the radiofrequency heating is modeled by the Arrhenius equation. The effects of size and position of a heterogeneous region in the original muscle tissue were first analyzed, in order to verify the possible existence of the functional re-entry arrhythmia during the time period considered in the simulations. For each case that exhibited re-entry arrhythmia, six different ablation procedures were analyzed, depending on the position of the radiofrequency electrode and heating time. The obtained results revealed the effects of different model parameters on the existence and possible mitigation of the functional re-entry arrhythmia.

Radiofrequency ablation for liver tumors abutting complex blood vessel structures: treatment protocol optimization using response surface method and computer modeling

OBJECTIVE

To achieve a result of a large tumor ablation volume with minimal thermal damage to the surrounding blood vessels by designing a few clinically-adjustable operating parameters in radiofrequency ablation (RFA) for liver tumors abutting complex vascular structures.

METHODS

Response surface method (RSM) was employed to correlate the ablated tumor volume (Ra) and thermal damage to blood vessels (Dt) based on RFA operating parameters: ablation time, electrode position, and insertion angle. A coupled electric-thermal-fluid RFA computer model was created as the testbed for RSM to simulate RFA process. Then, an optimal RFA protocol for the two conflicting goals, namely (1) large tumor ablation and (2) small thermal damage to the surrounding blood vessels, has been achieved under a specific ablation environment.

RESULTS

Linear regression analysis confirmed that the RFA protocol significantly affected Ra and Dt (the adjusted coefficient of determination Radj2 = 93.61% and 95.03%, respectively). For a proposed liver tumor scenario (liver tumor with a dimension of 4×3×2.9 cm³ abutting a complex vascular structure), an optimized RFA protocol was found based on the regression results in RSM. Compared with a reference RFA protocol, in which the electrode was centered in the tumor with a 12-min ablation time, the optimized RFA protocol has increased Ra  from 98.1% to 99.6% and decreased Dt from 4.1% to 0.4%, achieving nearly the complete ablation of proposed liver tumor and ignorable thermal damages to vessels.

CONCLUSION

This work showed that it is possible to design a few clinically-adjustable operating parameters of RFA for achieving a large tumor ablation volume while minimizing thermal damage to the surrounding blood vessels.

Multiscale and Multiphysics Modeling of Anisotropic Cardiac RFCA: Experimental-Based Model Calibration via Multi-Point Temperature Measurements

Radiofrequency catheter ablation (RFCA) is the mainstream treatment for drug-refractory cardiac fibrillation. Multiple studies demonstrated that incorrect dosage of radiofrequency energy to the myocardium could lead to uncontrolled tissue damage or treatment failure, with the consequent need for unplanned reoperations. Monitoring tissue temperature during thermal therapy and predicting the extent of lesions may improve treatment efficacy. Cardiac computational modeling represents a viable tool for identifying optimal RFCA settings, though predictability issues still limit a widespread usage of such a technology in clinical scenarios. We aim to fill this gap by assessing the influence of the intrinsic myocardial microstructure on the thermo-electric behavior at the tissue level. By performing multi-point temperature measurements on ex-vivo swine cardiac tissue samples, the experimental characterization of myocardial thermal anisotropy allowed us to assemble a fine-tuned thermo-electric material model of the cardiac tissue. We implemented a multiphysics and multiscale computational framework, encompassing thermo-electric anisotropic conduction, phase-lagging for heat transfer, and a three-state dynamical system for cellular death and lesion estimation. Our analysis resulted in a remarkable agreement between ex-vivo measurements and numerical results. Accordingly, we identified myocardium anisotropy as the driving effect on the outcomes of hyperthermic treatments. Furthermore, we characterized the complex nonlinear couplings regulating tissue behavior during RFCA, discussing model calibration, limitations, and perspectives.

Thyroid-dedicated internally-cooled wet electrode for benign thyroid nodules: experimental and clinical study

BACKGROUND

To assess the effects of radiofrequency ablation (RFA) using an internally-cooled wet (ICW) electrode in ex vivo bovine liver and evaluate the feasibility of the ICW electrode for benign thyroid nodules.

METHODS

We developed an 18-gauge ICW electrode with a microhole at the distal tip for tissue infusion of chilled (0 - 4 °C) isotonic saline (rate = 1.5 ml/min). RFA using ICW and IC electrodes were performed in bovine livers (40 pairs, 1-cm active tip, 50 W, 1-min). We compared the morphological characteristics of ablation zones and presence of carbonization. Twenty patients with benign thyroid nodules larger than 5 ml were prospectively enrolled in a clinical study and underwent ultrasound-guided RFA with ICW electrodes. Ultrasound examinations, laboratory data, and symptom and cosmetic scores were evaluated preprocedure and 1 and 6 months after the procedure.

RESULTS

In the ex vivo study, the ICW achieved significantly larger ablation zones than the IC (p<.001). In the clinical study, ICW electrodes were tolerable in all patients. At last follow-up, nodule volume had decreased from 15.6 ± 12.1 ml to 4.1 ± 4.3 ml (p<.001), and the mean volume reduction ratio (VRR) was 73.3 ± 13.7% at 6.0 months follow-up. Cosmetic and symptom scores were reduced from 3.52 ± 1.03 to 2.65 ± 0.88 and 3.10 ± 2.17 to 0.85 ± 0.99 (both p<.001), respectively. After RFA, thyroid function was well preserved in all patients, and mean thyroglobulin level decreased from 36.6 ± 52.1 ng/ml to 26.9 ± 62.2 ng/ml. One patient experienced a temporary voice change that recovered within a week.

CONCLUSIONS

We developed a thyroid-dedicated ICW electrode that we showed to be feasible and effective in patients with benign thyroid nodules.

Modeling and ex vivo experimental validation of liver tissue carbonization with laser ablation

OBJECTIVE

The purpose of this study was to model the process of liver tissue carbonization with laser ablation (LA).

METHODS

A dynamic heat source model was proposed and combined with the light distribution model as well as bioheat transfer model to predict the development of tissue carbonization with laser ablation (LA) using an ex vivo porcine liver tissue model. An ex vivo laser ablation experiment with porcine liver tissues using a custom-made 1064 nm bare fiber was then used to verify the simulation results at 3, 5, and 7 W laser administrations for 5 min. The spatiotemporal temperature distribution was monitored by measuring the temperature changes at three points close the fiber during LA. Both the experiment and simulation of the temperature, tissue carbonization zone, and ablation zone were then compared.

RESULTS

Four stages were recognized in the development of liver tissue carbonization during LA. The growth of the carbonization zone along the fiber axial and radial directions were different in the four stages. The carbonization zone along the fiber axial direction (L2) grew in the four stages with a sharp increase in the initial period and a minor increase in Stage 4. However, the change in the carbonization zone along the fiber radial direction (D2) increased dramatically (Stage 1) to a long-time plateau (Stages 2 and 3) followed by a slow growth in Stage 4. An acceptable agreement between the computer simulation and ex vivo experiment in the temperature changes at the three points was found at all three testing laser administrations. A similar result was also obtained for the dimensions of coagulation zone and ablation zone between the computer simulation and ex vivo experiment (carbonization zone: 2.99± 0.10 vs. 2.78 mm², 67.39± 0.09 vs. 63.53 mm², and 90.53± 0.11 vs. 85.15 mm²; ablation zone: 68.95± 0.28 vs. 65.29 mm², 182.11± 0.24 vs. 213.81 mm², and 244.80± 0.06 vs. 251.79 mm² at 3, 5, and 7 W, respectively).

CONCLUSION

This study demonstrates that the proposed dynamic heat source model combined with the light distribution model as well as bioheat transfer model can predict the development of liver tissue carbonization with an acceptable accuracy. This study contributes to an improved understanding of the LA process in the treatment of liver tumors.

Injectable Immunotherapeutic Thermogel for Enhanced Immunotherapy Post Tumor Radiofrequency Ablation

Tumor radiofrequency ablation (RFA) is a local and minimally invasive application using high temperature to induce coagulative necrosis of tumor, which has been commonly used in clinic. Although the tumor fragments generated by RFA can activate the host's immune system, it may be insufficient to inhibit cancer recurrence due to many factors such as the inefficient antigen presentation by dendritic cells (DCs). In this research, a convenient local administration strategy by blocking rho-associated kinases (ROCK) is applied to amplify the immune responses triggered by RFA via promoting the phagocytosis capacity of DCs. Briefly, ROCK inhibitor, Y27632, is successfully dispersed in the amphiphilic copolymer poly(D,L-lactide-co-glycolide)-b-poly(ethyleneglycol)-b-poly(D,L-lactideco-glycolide) (PLGA-PEG-PLGA) solution, which is sol at room temperature and forms hydrogel quickly at body temperature, obviously prolonging the retention of Y27632 after injection. Interestingly, in the melanoma tumor model, the generated tumor fragments after RFA treatment are swallowed by DCs and undergo reinforced antigen presentation process with the help of gradual released Y27632, further effectively activating T cell mediated anti-tumor immune responses and significantly improving the therapeutic efficiency of RFA. Overall, such strategy remarkably prolongs the survival of mice after RFA treatment, showing great potential for clinical translation as an improvement strategy for RFA.

How does saline backflow affect the treatment of saline-infused radiofrequency ablation?

BACKGROUND AND OBJECTIVE

Saline infusion is applied together with radiofrequency ablation (RFA) to enlarge the ablation zone. However, one of the issues with saline-infused RFA is backflow, which spreads saline along the insertion track. This raises the concern of not only thermally ablating the tissue within the backflow region, but also the loss of saline from the targeted tissue, which may affect the treatment efficacy.

METHODS

In the present study, 2D axisymmetric models were developed to investigate how saline backflow influence saline-infused RFA and whether the aforementioned concerns are warranted. Saline-infused RFA was described using the dual porosity-Joule heating model. The hydrodynamics of backflow was described using Poiseuille law by assuming the flow to be similar to that in a thin annulus. Backflow lengths of 3, 4.5, 6 and 9 cm were considered.

RESULTS

Results showed that there is no concern of thermally ablating the tissue in the backflow region. This is due to the Joule heating being inversely proportional to distance from the electrode to the fourth power. Results also indicated that larger backflow lengths led to larger growth of thermal damage along the backflow region and greater decrease in coagulation volume. Hence, backflow needs to be controlled to ensure an effective treatment of saline-infused RFA.

CONCLUSIONS

There is no risk of ablating tissues around the needle insertion track due to backflow. Instead, the risk of underablation as a result of the loss of saline due to backflow was found to be of greater concern.

Fast calculation of 3D radiofrequency ablation zone based on a closed-form solution of heat conduction equation fitted by ex vivo measurements

Fast calculation or simulation of the ablation zone induced by radiofrequency ablation (RFA) has a critical role in hepatic RFA planning and therapy. However, it remains challenging to approximate the ablation zone in real time, especially when more than one probe is involved in one ablation session. This paper presents a novel computational technique to calculate the 3D ablation zone of one probe RFA and two-probe switching RFA. The main idea is to get an approximate solution of the temperature distribution from a simplified Pennes bioheat equation, and further fit the solution to the coagulation measurements on ex vivo porcine liver. With a closed-form solution of temperature distribution, the calculation of the ablation zone is as simple as the commonly used ellipsoidal model, but it allows a more realistic prediction of combined ablation zones with different inter-probe spacing. The new approximation technique could potentially replace the original ellipsoidal model in the intervention planning step.

Irreversible Electroporation Enhanced by Radiofrequency Ablation: An In Vitro and Computational Study in a 3D Liver Tumor Model

In the present study, we used a computational and experimental study in a 3D liver tumor model (LTM) to explore the tumor ablation enhancement of irreversible electroporation (IRE) by pre-heating with radiofrequency ablation (RFA) and elucidate the mechanism whereby this enhancement occurs. Three ablation protocols, including IRE alone, RFA45 → IRE (with the pre-heating temperature of 45 °C), and RFA60 → IRE (with the pre-heating temperature of 60 °C) were investigated. Both the thermal conductivity and electrical conductivity of the 3D LTM were characterized with the change in the pre-heating temperature. The results showed, compared to IRE alone, a significant increase in the tumor ablation volume (19.59 [Formula: see text] 0.61 vs. 15.29 ± 0.61 mm³, p = 0.002 and 22.87 [Formula: see text] 0.35 vs. 15.29 ± 0.61 mm³, p < 0.001) was observed with both RFA45 → IRE and RFA60 → IRE, leading to a decrease in lethal electric filed strength (8 and 17%, correspondingly). The mechanism can be attributed to the change of cell microenvironment by pre-heating and/or a synergistic effect of RFA and IRE. The proposed enhancing method might contribute to the improvement of interventional oncology in the treatment of large tumors close to critical organs (e.g., large blood vessels and bile ducts).

Parametric evaluation of impedance curve in radiofrequency ablation: A quantitative description of the asymmetry and dynamic variation of impedance in bovine ex vivo model

Radiofrequency ablation (RFA) is a treatment for liver tumors with advantages over the traditional treatment of surgical resection. This procedure has the shortest recovery time in early stage tumors. The objective of this study is to parameterize the impedance curve of the RFA procedure in an ex vivo model by defining seven parameters (t_1/2, t_minimum, t_end, Z_initial, Z_1/2, Z_minimum and Z_end). Based on these parameters, three performance indices are defined: one to identify the magnitude of impedance curve asymmetry (δ), one Drop ratio (DR) describing the percentage of impedance decrease until the minimum impedance point is reached, and Ascent Ratio (AR) describing the magnitude of increase in impedance from the minimum impedance point to its maximum point. Fifty ablations were performed in a bovine ex vivo model to measure and evaluate the proposed parameters and performance index. The results show that the groups had an average δ of 29.02%, DR of 22.41%, and AR of 545.33% for RFA without the use of saline or deionized solutions. The saline solution and deionized water-cooled groups indicated the correlation of performance indices δ, DR, and AR with the obtained final ablation volume. Therefore, by controlling these parameters and indices, lower recurrence is achieved.

Effect of aging on heat transfer, fluid flow and drug transport in anterior human eye: A computational study

There are a lot of geometrical and morphological changes that happen in the human eye with age. Primary open-angle glaucoma, which is caused by the increase in intraocular pressure inside the anterior chamber of the eye is also associated with the physiological aging of the eye. Therefore, it is crucial to understand the effects of aging on drug delivery in the human eye when applied topically. Consequently, a numerical model of topical drug delivery for an aging human eye has been developed using commercial software COMSOL Multiphysics in the current study. Three different age groups (young, middle and old) have been considered and the changes in geometrical and tissue properties of different domains of the eye with age have been included in the numerical model. The effect of aging on heat transfer, aqueous humor flow, intraocular pressure and drug concentration in different domains and orientations of the eye have been investigated. Additionally, an attempt has been made to predict the best class of anti-glaucomatic treatment in silico that should be preferred to treat primary open-angle glaucoma effectively. Results illustrate that there is a decrease in the average corneal temperature and an increase in the temperature deviation across the cornea with age. Further, there is a decrease in the aqueous humor flow magnitude in the anterior chamber of the eye and an increase in intraocular pressure in the anterior chamber of older age groups, which leads to primary open-angle glaucoma. The reduced aqueous humor flow leads to increased drug concentration in the anterior chamber as well as iris and reduced drug concentration in the trabecular mesh of the older age groups, thereby affecting the treatment efficacy. Additionally, our simulated results demonstrate that anti-glaucomatic treatments should be more focused on treating the trabecular mesh rather than the ciliary body of the eye.

Modelling of combination therapy using implantable anticancer drug delivery with thermal ablation in solid tumor

Local implantable drug delivery system (IDDS) can be used as an effective adjunctive therapy for solid tumor following thermal ablation for destroying the residual cancer cells and preventing the tumor recurrence. In this paper, we develop comprehensive mathematical pharmacokinetic/pharmacodynamic (PK/PD) models for combination therapy using implantable drug delivery system following thermal ablation inside solid tumors with the help of molecular communication paradigm. In this model, doxorubicin (DOX)-loaded implant (act as a transmitter) is assumed to be inserted inside solid tumor (acts as a channel) after thermal ablation. Using this model, we can predict the extracellular and intracellular concentration of both free and bound drugs. Also, Impact of the anticancer drug on both cancer and normal cells is evaluated using a pharmacodynamic (PD) model that depends on both the spatiotemporal intracellular concentration as well as characteristics of anticancer drug and cells. Accuracy and validity of the proposed drug transport model is verified with published experimental data in the literature. The results show that this combination therapy results in high therapeutic efficacy with negligible toxicity effect on the normal tissue. The proposed model can help in optimize development of this combination treatment for solid tumors, particularly, the design parameters of the implant.

Remotely Activated Nanoparticles for Anticancer Therapy

Cancer has nowadays become one of the leading causes of death worldwide. Conventional anticancer approaches are associated with different limitations. Therefore, innovative methodologies are being investigated, and several researchers propose the use of remotely activated nanoparticles to trigger cancer cell death. The idea is to conjugate two different components, i.e., an external physical input and nanoparticles. Both are given in a harmless dose that once combined together act synergistically to therapeutically treat the cell or tissue of interest, thus also limiting the negative outcomes for the surrounding tissues. Tuning both the properties of the nanomaterial and the involved triggering stimulus, it is possible furthermore to achieve not only a therapeutic effect, but also a powerful platform for imaging at the same time, obtaining a nano-theranostic application. In the present review, we highlight the role of nanoparticles as therapeutic or theranostic tools, thus excluding the cases where a molecular drug is activated. We thus present many examples where the highly cytotoxic power only derives from the active interaction between different physical inputs and nanoparticles. We perform a special focus on mechanical waves responding nanoparticles, in which remotely activated nanoparticles directly become therapeutic agents without the need of the administration of chemotherapeutics or sonosensitizing drugs.

Computational Modeling of Cardiac Ablation Incorporating Electrothermomechanical Interactions

The application of radio frequency ablation (RFA) has been widely explored in treating various types of cardiac arrhythmias. Computational modeling provides a safe and viable alternative to ex vivo and in vivo experimental studies for quantifying the effects of different variables efficiently and reliably, apart from providing a priori estimates of the ablation volume attained during cardiac ablation procedures. In this contribution, we report a fully coupled electrothermomechanical model for a more accurate prediction of the treatment outcomes during the radio frequency cardiac ablation. A numerical model comprising of cardiac tissue and the cardiac chamber has been developed in which an electrode has been inserted perpendicular to the cardiac tissue to simulate actual clinical procedures. Temperature-dependent heat capacity, electrical and thermal conductivities, and blood perfusion rate have been considered to model more realistic scenarios. The effects of blood flow and contact force of the electrode tip on the treatment outcomes of a fully coupled model of RFA have been systematically investigated. The numerical study demonstrates that the predicted ablation volume of RFA is significantly dependent on the blood flow rate in the cardiac chamber and also on the tissue deformation induced due to electrode insertion depth of 1.5 mm or higher.

Directional ablation in radiofrequency ablation using a multi-tine electrode functioning in multipolar mode: An in-silico study using a finite set of states

PURPOSE

To analyse the feasibility of directional ablation using a multi-tine electrode.

METHODS

A multi-tine electrode capable of operating in multipolar mode has been used to study the directional ablation. In addition to the basic design, similar to commercially available FDA approved multi-tine electrode, tines have been insulated from each other inside the probe base and tip using a thin insulating material of thickness 0.25 mm. A cylindrical single-compartment model of size 6 cm × 6 cm has been used to model normal liver tissue. The temperature-controlled radiofrequency ablation has been employed to maintain the tine-tips at different temperatures. Electro-thermal simulations have been performed by using a commercial multi-physics software package based on finite element methods. To make this study feasible a new approach to predict the ablations have been proposed and used in this study.

RESULTS

Asymmetric ablation zone with up to 5 mm difference in ablation boundary between the intended and non-intended direction has been observed along the transverse direction. Reduction in ablation up to 5 mm along the axial direction in comparison to the monopolar mode has also been observed.

CONCLUSION

Multi-tine electrode modified to operate in multipolar mode can create directional ablations of different shapes and can be used to target position and shape specific tumours.

An Noninvasive and Impedance-Ignored Control Strategy of the Ablation Zone in Radiofrequency Ablation Therapy

This study proposed a control strategy of the ablation margin using the temperature of the probe, without causing additional damage. Compared with other methods, the proposed strategy is real time and impedance-ignored, thus has a better performance in practice. A theoretical model was established to obtain the temperature distribution during the treatment. Several functions were obtained by fitting the results of the simulation model, with which a preset central temperature curve corresponding to a desired ablation zone was determined to regulate the temperature of the control point. Considering the various impedances in practice, a voltage adjustment method according to the error between the preset central temperature and the practical central temperature was proposed to minimize the effect of impedances. At last, the strategy was verified with phantom experiments. The results show that all the temperatures of the control points reached to 50°C at a specific time and kept for a while, which demonstrated the strategy had a good performance within the error range allowed.

Domain Heterogeneity in Radiofrequency Therapies for Pain Relief: A Computational Study with Coupled Models

The objective of the current research work is to study the differences between the predicted ablation volume in homogeneous and heterogeneous models of typical radiofrequency (RF) procedures for pain relief. A three-dimensional computational domain comprising of the realistic anatomy of the target tissue was considered in the present study. A comparative analysis was conducted for three different scenarios: (a) a completely homogeneous domain comprising of only muscle tissue, (b) a heterogeneous domain comprising of nerve and muscle tissues, and (c) a heterogeneous domain comprising of bone, nerve and muscle tissues. Finite-element-based simulations were performed to compute the temperature and electrical field distribution during conventional RF procedures for treating pain, and exemplified here for the continuous case. The predicted results reveal that the consideration of heterogeneity within the computational domain results in distorted electric field distribution and leads to a significant reduction in the attained ablation volume during the continuous RF application for pain relief. The findings of this study could provide first-hand quantitative information to clinical practitioners about the impact of such heterogeneities on the efficacy of RF procedures, thereby assisting them in developing standardized optimal protocols for different cases of interest.

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.

Chemical Enhancement of Irreversible Electroporation: A Review and Future Suggestions

Irreversible electroporation has raised great interest in the past decade as a means of destroying cancers in a way that does not involve heat. Irreversible electroporation is a novel ablation technology that uses short high-voltage electrical pulses to enhance the permeability of tumor cell membranes and generate irreversible nano-sized structural defects or pores, thus leading to cell death. Irreversible electroporation has many advantages over thermal therapies due to its nonthermal mechanism: (1) reduced risk of injury to surrounding organs and (2) no “heat-sink” effect due to nearby blood vessels. However, so far, it has been difficult for irreversible electroporation to completely ablate large tumors (eg, >3 cm in diameter). In order to overcome this problem, many preclinical and clinical studies have been performed to improve the efficacy of IRE in the treatment of large size of tumors through a chemical perspective. Due to the distribution of electric field, irreversible electroporation region, reversible electroporation region, and intact region can be found in the treatment of irreversible electroporation. Thus, 2 types of chemical enhancements of irreversible electroporation were discussed in the article, such as the reversible electroporation region enhanced and the irreversible electroporation region enhanced. Specifically, the state-of-the-art results regarding the following approaches that have the potential to be used in the enhancement of irreversible electroporation were systematically reviewed in the article, including (1) combination with cytotoxic drugs, (2) calcium electroporation, (3) modification of cell membrane, and (4) modification of the tumor cell microenvironment. In the end, we concluded with 4 issues that should be addressed in the future for improving irreversible electroporation further in a chemical way.

Radiofrequency ablation with four electrodes as a building block for matrix radiofrequency ablation: Ex vivo liver experiments and finite element method modelling. Influence of electric and activation mode on coagulation size and geometry

PURPOSE

Radiofrequency ablation (RFA) is increasingly being used to treat unresectable liver tumors. Complete ablation of the tumor and a safety margin is necessary to prevent local recurrence. With current electrodes, size and shape of the ablation zone are highly variable leading to unsatisfactory local recurrence rates, especially for tumors >3 cm. In order to improve predictability, we recently developed a system with four simple electrodes with complete ablation in between the electrodes. This rather small but reliable ablation zone is considered as a building block for matrix radiofrequency ablation (MRFA). In the current study we explored the influence of the electric mode (monopolar or bipolar) and the activation mode (consecutive, simultaneous or switching) on the size and geometry of the ablation zone.

MATERIALS AND METHODS

The four electrode system was applied in ex vivo bovine liver. The electric and the activation mode were changed one by one, using constant power of 50 W in all experiments. Size and geometry of the ablation zone were measured. Finite element method (FEM) modelling of the experiment was performed.

RESULTS

In ex vivo liver, a complete and predictable coagulation zone of a 3 × 2 × 2 cm block was obtained most efficiently in the bipolar simultaneous mode due to the combination of the higher heating efficacy of the bipolar mode and the lower impedance by the simultaneous activation of four electrodes, as supported by the FEM simulation.

CONCLUSIONS

In ex vivo liver, the four electrode system used in a bipolar simultaneous mode offers the best perspectives as building block for MRFA. These results should be confirmed by in vivo experiments.

Shape-shifting thermal coagulation zone during saline-infused radiofrequency ablation: A computational study on the effects of different infusion location

BACKGROUND AND OBJECTIVE

The majority of the studies on radiofrequency ablation (RFA) have focused on enlarging the size of the coagulation zone. An aspect that is crucial but often overlooked is the shape of the coagulation zone. The shape is crucial because the majority of tumours are irregularly-shaped. In this paper, the ability to manipulate the shape of the coagulation zone following saline-infused RFA by altering the location of saline infusion is explored.

METHODS

A 3D model of the liver tissue was developed. Saline infusion was described using the dual porosity model, while RFA was described using the electrostatic and bioheat transfer equations. Three infusion locations were investigated, namely at the proximal end, the middle and the distal end of the electrode. Investigations were carried out numerically using the finite element method.

RESULTS

Results indicated that greater thermal coagulation was found in the region of tissue occupied by the saline bolus. Infusion at the middle of the electrode led to the largest coagulation volume followed by infusion at the proximal and distal ends. It was also found that the ability to delay roll-off, as commonly associated with saline-infused RFA, was true only for the case when infusion is carried out at the middle. When infused at the proximal and distal ends, the occurrence of roll-off was advanced. This may be due to the rapid and more intense heating experienced by the tissue when infusion is carried out at the electrode ends where Joule heating is dominant.

CONCLUSION

Altering the location of saline infusion can influence the shape of the coagulation zone following saline-infused RFA. The ability to 'shift' the coagulation zone to a desired location opens up great opportunities for the development of more precise saline-infused RFA treatment that targets specific regions within the tissue.

Conformal coverage of liver tumors by the thermal coagulation zone in 2450-MHz microwave ablation

Purpose: To optimize treatment schemes using 2450-MHz microwave ablation (MWA), a novel conformal coverage method based on bipolar-angle mapping is proposed that determines whether a liver tumor is completely encompassed by thermal coagulation zones. Materials and methods: Firstly, three-dimensional (3-D) triangular mesh data of liver tumors were reconstructed from clinical computed tomography (CT) slices using the Marching cubes (MC) algorithm. Secondly, characterization models of thermal coagulation zones were established based on finite element simulation results of 40, 45, 50, 55, and 60 W ablations. Finally, coagulation zone models and tumor surface data were mapped and fused on a two-dimensional (2-D) plane to achieve conformal coverage of liver tumors by comparing the corresponding polar radii. Results: Optimal parameters for ablation treatment of liver tumors were efficiently obtained with the proposed conformal coverage method. Fifteen liver tumors were obtained with maximal diameters of 12.329-78.612 mm (mean ± standard deviation, 39.094 ± 19.447 mm). The insertion positions and orientations of the MWA antenna were determined based on 3-D reconstruction results of these tumors. The ablation patterns and durations of tumors were planned according to the minimum mean standard deviations between the ablative margin and tumor surface. Conclusion: The proposed method can be applied to computer-assisted MWA treatment planning of liver tumors, and is expected to guide clinical procedures in future.

A Novel Method to Increase Tumor Ablation Zones With RFA by Injecting the Cationic Polymer Solution to Tissues: In Vivo and Computational Studies

OBJECTIVE

This study aims to examine, for the first time, the introduction of cationic polymer solutions to improve radiofrequency ablation (RFA) in terms of a potentially enlarged ablation zone.

METHODS

By using in vivo and computational RFA studies, two cationic polymers, Chitooligosaccharides (COS) and carboxymethyl chitosan (CMC), diluted in deionized water, were injected into tissues separately surrounding the RF bipolar electrode prior to power application. A total of 9 rabbits were used to 1) measure the increase in electrical conductivity of tissues injected with the cationic polymer solutions, and 2) explore the enhancement of the ablation performance in RFA trials. A computer model of RFA comprising a model of the solution diffusion with an RF thermal ablation model was also built, validated by the in vivo experiment, to quantitatively study the effect of cationic polymer solutions on ablation performances.

RESULTS

Compared to the control group, the electrical conductivity of rabbit liver tissues was increased by 42.20% (0.282 ± 0.006 vs. 0.401 ± 0.048 S/m, P = 0.001) and 43.97% (0.282 ± 0.006 vs. 0.406 ± 0.042 S/m, P = 0.001) by injecting the COS and CMC solution at the concentration of 100 mg/mL into the tissues, denoted COS_DW100 and CMC_DW100, respectively. Consequently, the in vivo experiments show that the ablation zone was enlarged by 95% (47.6 ± 6.3 vs. 92.6 ± 11.5 mm², P < 0.001) and 87% (47.6± 6.3 vs. 88.8 ± 9.6 mm², P < 0.001) by COS_DW100 and CMC_DW100, respectively. The computer simulation shows that the ablation zone was enlarged by 71% (51.9 vs. 88.7 mm²) and 63% (51.9 vs. 84.7 mm²) by COS_DW100 and CMC_DW100, respectively.

CONCLUSION

The injection of the cationic solution can greatly improve the performance of RFA treatment in terms of enlarging the ablation zone, which is due to the increase in the electrical conductivity of liver tissues surrounding the RF electrode.

SIGNIFICANCE

This study contributes to the improvement of RFA in the treatment of large tumors.

Steerable catheters for minimally invasive surgery: a review and future directions

The steerable catheter refers to the catheter that is manipulated by a mechanism which may be driven by operators or by actuators. The steerable catheter for minimally invasive surgery has rapidly become a rich and diverse area of research. Many important achievements in design, application and analysis of the steerable catheter have been made in the past decade. This paper aims to provide an overview of the state of arts of steerable catheters. Steerable catheters are classified into four main groups based on the actuation principle: (1) tendon driven catheters, (2) magnetic navigation catheters, (3) soft material driven catheters (shape memory effect catheters, steerable needles, concentric tubes, conducting polymer driven catheters and hydraulic pressure driven catheters), and (4) hybrid actuation catheters. The advantages and limitations of each of them are commented and discussed in this paper. The future directions of research are summarized.

A computational model to investigate the influence of electrode lengths on the single probe bipolar radiofrequency ablation of the liver

BACKGROUND AND OBJECTIVES

Recently, there have been calls for RFA to be implemented in the bipolar mode for cancer treatment due to the benefits it offers over the monopolar mode. These include the ability to prevent skin burns at the grounding pad and to avoid tumour track seeding. The usage of bipolar RFA in clinical practice remains uncommon however, as not many research studies have been carried out on bipolar RFA. As such, there is still uncertainty in understanding the effects of the different RF probe configurations on the treatment outcome of RFA. This paper demonstrates that the electrode lengths have a strong influence on the mechanics of bipolar RFA. The information obtained here may lead to further optimization of the system for subsequent uses in the hospitals.

METHODS

A 2D model in the axisymmetric coordinates was developed to simulate the electro-thermophysiological responses of the tissue during a single probe bipolar RFA. Two different probe configurations were considered, namely the configuration where the active electrode is longer than the ground and the configuration where the ground electrode is longer than the active. The mathematical model was first verified with an existing experimental study found in the literature.

RESULTS

Results from the simulations showed that heating is confined only to the region around the shorter electrode, regardless of whether the shorter electrode is the active or the ground. Consequently, thermal coagulation also occurs in the region surrounding the shorter electrode. This opened up the possibility for a better customized treatment through the development of RF probes with adjustable electrode lengths.

CONCLUSIONS

The electrode length was found to play a significant role on the outcome of single probe bipolar RFA. In particular, the length of the shorter electrode becomes the limiting factor that influences the mechanics of single probe bipolar RFA. Results from this study can be used to further develop and optimize bipolar RFA as an effective and reliable cancer treatment technique.

Tumor Ablation Enhancement by Combining Radiofrequency Ablation and Irreversible Electroporation: An In Vitro 3D Tumor Study

We hypothesized and demonstrated for the first time that significant tumor ablation enhancement can be achieved by combining radiofrequency ablation (RFA) and irreversible electroporation (IRE) using a 3D cervical cancer cell model. Three RFA (43, 50, and 60 °C for 2 min) and IRE protocols (350, 700, and 1050 V/cm) were used to study the combining effect in the 3D tumor cell model. The in vitro experiment showed that both RFA enhanced IRE and IRE enhanced RFA can lead to a significant increase in the size of the ablation zone compared to IRE and RFA alone. It was also noted that the sequence of applying ablation energy (RFA → RE or IRE → RFA) affected the efficacy of tumor ablation enhancement. The electrical conductivity of 3D tumor was found to be increased after preliminary RFA or IRE treatment. This increase in tumor conductivity may explain the enhancement of tumor ablation. Another explanation might be that there is repeat injury to the transitional zone of the first treatment by the second one. The promising results achieved in the study can provide us useful clues about the treatment of large tumors abutting large vessels or bile ducts.

Design of a Novel Electrode of Radiofrequency Ablation for Large Tumors: In Vitro Validation and Evaluation

In the present study, a monopolar expandable electrode (MEE) in radiofrequency ablation (RFA) proposed in our previous study was validated and evaluated using the in vitro experiment and computer simulation. Two commercial RF electrodes (conventional electrode, CE and umbrella electrode, UE) was used to compare the ablation results with MEE using the in vitro egg white model (experiment and computer simulation) and in vivo liver tumor model (computer simulation) to verify the efficacy of MEE in the large tumor ablation. The sharp increase in impedance during RFA procedures was taken as the termination of RFA protocols. The volume and sphericity of ablation zone generated by MEE, CE, and UE in the in vitro egg white experiment were 75.3 1.6 cm3, 2.7 0.4 cm3, 12.4 1.8 cm3 (P <0.001), and 88.1 0.9%, 12.9 1.3%, 62.0 3.0% (P <0.001), respectively. Correspondingly, a similar result was obtained in the egg white simulation. In the liver tumor simulation, the volume and sphpericity of ablation zone generated by MEE, CE, and UE were 35.4 cm3 and 86.8%, 3.7 cm3 and 17.7%, and 12.7 cm3 and 59.6%, respectively. In summary, MEE has the potential to achieve complete ablation in the treatment of large tumors (>3 cm in diameter) compared with CE and UE due to the larger electrode-tissue interface and more round shape of hooks.

RF ablation thermal simulation model: Parameter sensitivity analysis

OBJECTIVE:

The aim of the research is to obtain the relative influences of some critical electro-thermal parameters on the ablation temperature and lesion volume during temperature-controlled radiofrequency ablation (RFA) of liver tumor by parameter sensitivity analysis.

METHODS:

The finite element method (FEM) has been used to establish the simulation model of RFA temperature field, and the sensitivity of the tissue parameters has been analyzed. The effects of six parameters have been taken into account, including the thermal specific capacity (Cp), the thermal conductivity (k), the electrical conductivity (Sigma), the density (rho), the dielectric constant (Epsilon) and the resistance (R). The simulation processes based on different parameter values have been accomplished with Comsol Multiphysics software, and the sensitivity parameters have been obtained utilizing the variance contribution rate (SS%) or the main effects.

RESULTS:

It was found that the ablation temperature and lesion volume increased with increasing the values of Rand Sigma, but was a reverse situation for Cp and rho. Besides, the influence of k on ablation volume was relatively small and Epsilon had a negligible effect on ablation temperature.

CONCLUSIONS:

It is concluded that these parameter sensitivity results can provide scientific and reliable reference for the specificity analysis of the RF ablation models.

Roll-Off Displacement in Ex Vivo Experiments of RF Ablation With Refrigerated Saline Solution and Refrigerated Deionized Water

OBJECTIVE

The recurrence rate in the treatment of liver tumors using radio frequency ablation (RFA) is often related to incomplete tissue necrosis and consequently the limitation in the ablation volume. This paper proposes an ablation protocol combined with the infusion of saline solution and deionized water aiming at achieving a time displacement in the roll-off occurrence and consequently increasing the volume of ablation.

METHODS

An infusion of saline solution and deionized water at 5 and 23  ^°C was performed to evaluate the influence of these liquids on the RFA procedure in ex vivo bovine liver pieces. The obtained results were used to propose a mathematical model of the roll-off phenomenon by means of the system identification techniques.

RESULTS

The RFA combined with the infusion of saline solution 0.9% at 5  ^°C presented optimal results, with a time delay of the roll-off occurrence in 27.8% compared to pure RFA ( p = 0.002) and an increase in the necrotic volume of 51.2% ( p = 0.0002). Two Box-Jenkins models were obtained to describe the roll-off phenomenon: 1) pure RFA; and 2) RFA combined with the saline solution 0.9% at 5  ^°C.

CONCLUSION

The RFA therapy combined with the saline solution 0.9% at 5  ^°C increases the time range to the roll-off occurrence, leading to higher necrosis volumes in ex vivo bovine liver samples. The development of a mathematical model to describe the roll-off behavior demonstrated that the transient response is improved by the infusion of the saline solution 0.9% at 5  ^°C.

Optimization of Electrode Configuration and Pulse Strength in Irreversible Electroporation for Large Ablation Volumes Without Thermal Damage

The aim of this study was to analyze five factors that are responsible for the ablation volume and maximum temperature during the procedure of irreversible electroporation (IRE). The five factors used in this study were the pulse strength (U), the electrode diameter (B), the distance between the electrode and the center (D), the electrode length (L), and the number of electrodes (N). A validated finite element model (FEM) of IRE was built to collect the data of the ablation volume and maximum temperature generated in a liver tissue. Twenty-five experiments were performed, in which the ablation volume and maximum temperature were taken as response variables. The five factors with ranges were analyzed to investigate their impacts on the ablation volume and maximum temperature, respectively, using analysis of variance. Response surface method (RSM) was used to optimize the five factors for the maximum ablation volume without thermal damage (the maximum temperature ≤ 50 °C for 90 s). U and L were found with significant impacts on the ablation volume (P < 0.001, and P = 0.009, respectively) while the same conclusion was not found for B, D and N (P = 0.886, P = 0.075 and P = 0.279, respectively). Furthermore, U, D, and N had the significant impacts on the maximum temperature with P < 0.001, P < 0.001, and P = 0.003, respectively, while same conclusion was not found for B and L (P = 0.720 and P = 0.051, respectively). The maximum ablation volume of 2952.9960 mm3 without thermal damage can be obtained by using the following set of factors: U = 2362.2384 V, B = 1.4889 mm, D = 7 mm, L = 4.5659 mm, and N = 3. The study concludes that both B and N have insignificant impacts (P = 0.886, and P = 0.279, respectively) on the ablation volume; U has the most significant impact (P < 0.001) on the ablation volume; electrode configuration and pulse strength in IRE can be optimized for the maximum ablation volume without thermal damage using RSM.

Design of a Novel Electrode of Radiofrequency Ablation for Large Tumors: A Finite Element Study

The aim of the study was to design a novel radiofrequency (RF) electrode for larger and rounder ablation volumes and its ability to achieve the complete ablation of liver tumors larger than 3 cm in diameter using finite element method. A new RF expandable electrode comprising three parts (i.e., insulated shaft, changing shaft, and hooks) was designed. Two modes of this new electrode, such as monopolar expandable electrode (MEE) and hybrid expandable electrode (HEE), and a commercial expandable electrode (CEE) were investigated using liver tissue with (scenario I) and without (scenario II) a liver tumor. A temperature-controlled radiofrequency ablation (RFA) protocol with a target temperature of 95 °C and an ablation time of 15 min was used in the study. Both the volume and shape of the ablation zone were examined for all RF electrodes in scenario I. Then, the RF electrode with the best performance in scenario I and CEE were used to ablate a large liver tumor with the diameter of 3.5 cm (scenario II) to evaluate the effectiveness of complete tumor ablation of the designed RF electrode. In scenario I, the ablation volumes of CEE, HEE, and MEE were 12.11 cm3, 33.29 cm3, and 48.75 cm3, respectively. The values of sphericity index (SI) of CEE, HEE, and MEE were 0.457, 0.957, and 0.976, respectively. The best performance was achieved by using MEE. In scenario II, the ablation volumes of MEE and CEE were 71.59 cm3 and 19.53 cm3, respectively. Also, a rounder ablation volume was achieved by using MEE compared to CEE (SI: 0.978 versus 0.596). The study concluded that: (1) compared with CEE, both MEE and HEE get larger and rounder ablation volumes due to the larger electrode–tissue interface and rounder shape of hook deployment; (2) MEE has the best performance in getting a larger and rounder ablation volume; and (3) computer simulation result shows that MEE is also able to ablate a large liver tumor (i.e., 3.5 cm in diameter) completely, which has at least 0.785 cm safety margin.

Transport of Liposome Encapsulated Drugs in Voxelized Computational Model of Human Brain Tumors

There are many obstacles in the transport of chemotherapeutic drugs to tumor cells that lead to irregular and non-uniform uptake of drugs inside tumors. The study of these transport problems will help with accurate prediction of drug transport and optimizing treatment strategy. To this end, liposome mediated drug delivery has emerged as an excellent anticancer therapy due to its ability to deliver drugs at site of action and reducing the chances of side effects to the healthy tissues. In this paper, a computational fluid dynamics (CFD) model based on realistic vasculature of human brain tumor is presented. This model utilizes dynamic contrast enhanced-magnetic resonance imaging (DCE-MRI) data to account for heterogeneity in tumor vasculature. Porosity of the interstitial space inside the tumor and normal tissue is determined voxel-wise by processing the DCE-MRI images by general tracer kinetic model (GTKM). The CFD model is applied to predict transport of two different types of liposomes (stealth and conventional) in tumors. The amount of accumulated liposomes is compared with accumulated free drug (doxorubicin) in the interstitial space. Simulation results indicate that stealth liposomes accumulate more and remain for longer periods of time in tumors as compared with conventional liposomes and free drug. The present model provides us a qualitative and quantitative examination on the transport and deposition of liposomes as well as free drugs in actual human brain tumors.