Planning of hyperthermic treatment for malignant glioma using computer simulation

Design of a temperature-feedback controlled automated magnetic hyperthermia therapy device

Introduction

Magnetic hyperthermia therapy (MHT) is a minimally invasive adjuvant therapy capable of damaging tumors using magnetic nanoparticles exposed radiofrequency alternating magnetic fields. One of the challenges of MHT is thermal dose control and excessive heating in superficial tissues from off target eddy current heating.

Methods

We report the development of a control system to maintain target temperature during MHT with an automatic safety shutoff feature in adherence to FDA Design Control Guidance. A proportional-integral-derivative (PID) control algorithm was designed and implemented in NI LabVIEW^®. A standard reference material copper wire was used as the heat source to verify the controller performance in gel phantom experiments. Coupled electromagnetic thermal finite element analysis simulations were used to identify the initial controller gains.

Results

Results showed that the PID controller successfully achieved the target temperature control despite significant perturbations.

Discussion and Conclusion

Feasibility of PID control algorithm to improve efficacy and safety of MHT was demonstrated.

Post-treatment analysis of irreversible electroporation waveforms delivered to human pancreatic cancer patients

Irreversible electroporation (IRE) is a focal ablation therapy that uses high voltage, short electrical pulses to destroy tumor tissue. The success of treatment directly depends on exposure of the entire tumor to a lethal electric field magnitude. However, this exposure is difficult to predict ahead of time and it is challenging for clinicians to determine optimal treatment parameters. One method clinicians rely upon for the cessation of pulse delivery is to monitor the resistance value of the tissue, as the cells within the tissue will undergo changes during electroporation. This work presents a computational model which incorporates human pancreatic tumor conductivity, and compares predicted and measured output currents from IRE treatments of human patients. The measured currents vary widely from patient to patient, suggesting there may areas of high local conductivity in the treatment area.

Role of Simulations in the Treatment Planning of Radiofrequency Hyperthermia Therapy in Clinics

Hyperthermia therapy is a treatment modality in which tumor temperatures are elevated to higher temperatures to cause damage to cancerous tissues. Numerical simulations are integral in the development of hyperthermia treatment systems and in clinical treatment planning. In this study, simulations in radiofrequency hyperthermia therapy are reviewed in terms of their technical development and clinical aspects for effective clinical use. This review offers an overview of mathematical models and the importance of tissue properties; locoregional mild hyperthermia therapy, including phantom and realistic human anatomy models; phase array systems; tissue damage; thermal dose analysis; and thermoradiotherapy planning. This review details the improvements in numerical approaches in treatment planning and their application for effective clinical use. Furthermore, the modeling of thermoradiotherapy planning, which can be integrated with radiotherapy to provide combined hyperthermia and radiotherapy treatment planning strategies, are also discussed. This review may contribute to the effective development of thermoradiotherapy planning in clinics.

The Feasibility of Enhancing Susceptibility of Glioblastoma Cells to IRE Using a Calcium Adjuvant

Irreversible electroporation (IRE) is a cellular ablation method used to treat a variety of cancers. IRE works by exposing tissues to pulsed electric fields which cause cell membrane disruption. Cells exposed to lower energies become temporarily permeable while greater energy exposure results in cell death. For IRE to be used safely in the brain, methods are needed to extend the area of ablation without increasing applied voltage, and thus, thermal damage. We present evidence that IRE used with adjuvant calcium (5 mM CaCl₂) results in a nearly twofold increase in ablation area in vitro compared to IRE alone. Adjuvant 5 mM CaCl₂ induces death in cells reversibly electroporated by IRE, thereby lowering the electric field thresholds required for cell death to nearly half that of IRE alone. The calcium-induced death response of reversibly electroporated cells is confirmed by electrochemotherapy pulses which also induced cell death with calcium but not without. These findings, combined with our numerical modeling, suggest the ability to ablate up to 3.2× larger volumes of tissue in vivo when combining IRE and calcium. The ability to ablate a larger volume with lowered energies would improve the efficacy and safety of IRE therapy.

3D perfused brain phantom for interstitial ultrasound thermal therapy and imaging: design, construction and characterization

Thermal therapy has emerged as an independent modality of treating some tumors. In many clinics the hyperthermia, one of the thermal therapy modalities, has been used adjuvant to radio- or chemotherapy to substantially improve the clinical treatment outcomes. In this work, a methodology for building a realistic brain phantom for interstitial ultrasound low dose-rate thermal therapy of the brain is proposed. A 3D brain phantom made of the tissue mimicking material (TMM) had the acoustic and thermal properties in the 20-32 °C range, which is similar to that of a brain at 37 °C. The phantom had 10-11% by mass of bovine gelatin powder dissolved in ethylene glycol. The TMM sonicated at 1 MHz, 1.6 MHz and 2.5 MHz yielded the amplitude attenuation coefficients of 62  ±  1 dB m(-1), 115  ±  4 dB m(-1) and 175  ±  9 dB m(-1), respectively. The density and acoustic speed determination at room temperature (~24 °C) gave 1040  ±  40 kg m(-3) and 1545  ±  44 m s(-1), respectively. The average thermal conductivity was 0.532 W m(-1) K(-1). The T1 and T2 values of the TMM were 207  ±  4 and 36.2  ±  0.4 ms, respectively. We envisage the use of our phantom for treatment planning and for quality assurance in MRI based temperature determination. Our phantom preparation methodology may be readily extended to other thermal therapy technologies.

A parametric study delineating irreversible electroporation from thermal damage based on a minimally invasive intracranial procedure

BACKGROUND

Irreversible electroporation (IRE) is a new minimally invasive technique to kill undesirable tissue in a non-thermal manner. In order to maximize the benefits from an IRE procedure, the pulse parameters and electrode configuration must be optimized to achieve complete coverage of the targeted tissue while preventing thermal damage due to excessive Joule heating.

METHODS

We developed numerical simulations of typical protocols based on a previously published computed tomographic (CT) guided in vivo procedure. These models were adapted to assess the effects of temperature, electroporation, pulse duration, and repetition rate on the volumes of tissue undergoing IRE alone or in superposition with thermal damage.

RESULTS

Nine different combinations of voltage and pulse frequency were investigated, five of which resulted in IRE alone while four produced IRE in superposition with thermal damage.

CONCLUSIONS

The parametric study evaluated the influence of pulse frequency and applied voltage on treatment volumes, and refined a proposed method to delineate IRE from thermal damage. We confirm that determining an IRE treatment protocol requires incorporating all the physical effects of electroporation, and that these effects may have significant implications in treatment planning and outcome assessment. The goal of the manuscript is to provide the reader with the numerical methods to assess multiple-pulse electroporation treatment protocols in order to isolate IRE from thermal damage and capitalize on the benefits of a non-thermal mode of tissue ablation.

Intracranial nonthermal irreversible electroporation: in vivo analysis

Nonthermal irreversible electroporation (NTIRE) is a new minimally invasive technique to treat cancer. It is unique because of its nonthermal mechanism of tumor ablation. Intracranial NTIRE procedures involve placing electrodes into the targeted area of the brain and delivering a series of short but intense electric pulses. The electric pulses induce irreversible structural changes in cell membranes, leading to cell death. We correlated NTIRE lesion volumes in normal brain tissue with electric field distributions from comprehensive numerical models. The electrical conductivity of brain tissue was extrapolated from the measured in vivo data and the numerical models. Using this, we present results on the electric field threshold necessary to induce NTIRE lesions (495-510 V/cm) in canine brain tissue using 90 50-mus pulses at 4 Hz. Furthermore, this preliminary study provides some of the necessary numerical tools for using NTIRE as a brain cancer treatment. We also computed the electrical conductivity of brain tissue from the in vivo data (0.12-0.30 S/m) and provide guidelines for treatment planning and execution. Knowledge of the dynamic electrical conductivity of the tissue and electric field that correlates to lesion volume is crucial to ensure predictable complete NTIRE treatment while minimizing damage to surrounding healthy tissue.

Interstitial Hyperthermia With Intra-arterial Injection of Adriamycin for Malignant Glioma

A new method for treating malignant glioma by concurrent intra-arterial injection of adriamycin during thermotherapy was performed in seven patients with malignant glioma, four males and three females, with five cases of glioblastoma and two of anaplastic oligodendroglioma. Adriamycin was intra-arterially injected at a dose of 20 mg via the common carotid artery during thermotherapy. The heating procedure was repeated three times combined with chemotherapy in one therapy course, and a total of nine therapy courses were performed in the seven patients. All patients tolerated the protocol well. Based on post-therapy computed tomography, five of the therapy courses achieved partial response, one course resulted in disease progression, and the remaining three courses showed no change. The median time to progression was 3.4 months and the overall median length of survival following stereotactic biopsy was 13.2 months. Facial flushing was observed during eight therapy courses, and extensive alopecia in six therapy courses. Intracystic concentrations of adriamycin were determined in three patients, and marked increases were observed. Intra-arterial injection chemotherapy during hyperthermia is a promising therapeutic method for treatment of malignant glioma with few adverse effects.

Mild hyperthermia plus adenoviral p53 over-expression additively inhibits the viability of human malignant glioma cells

Adenoviral replacement of the p53 gene has already been proved effective for the treatment of various tumours, including malignant gliomas. However, it is difficult to treat malignant glioma with p53 gene therapy alone because of problems with resistance or a less-than-satisfactory response to the treatment. This study investigated whether heat shock at 43 degrees C (mild hyperthermia) augments the cytotoxic effect of p53 gene transfer on malignant glioma cells expressing wild-type p53 (D54) or mutant p53 (U373-MG and U251-MG). The combination of mild hyperthermia and adenoviral p53 over-expression had an additive inhibitory effect on cellular proliferation in all three cell lines studied. Further, both cell cycle analysis and a DNA fragmentation assay showed that apoptosis was induced by p53 over-expression alone but not by heat shock at 43 degrees C alone. However, p53 over-expression followed by mild hyperthermia additively increased the proportion of cells in which apoptosis was induced, regardless of the endogenous p53 status of the tumour cells. Interestingly, a caspase-independent mechanism was observed to be involved in the p53-induced apoptosis in U251-MG and D54 cells. Taken together, the findings showed that combining adenoviral p53 transfer with mild hyperthermia inhibits the proliferation of malignant glioma cells in an additive manner, irrespective of their endogenous p53 status, suggesting a novel treatment strategy for this malignancy.

Mild heat shock induces autophagic growth arrest, but not apoptosis in U251-MG and U87-MG human malignant glioma cells

Although hyperthermia has been used as a treatment of malignant brain tumors, it is not yet clear what is the mechanism of the cell growth inhibition by heat shock, especially by the temperature which has clinically been applied to tumor-brain border-zone, 42-43 degrees C. Therefore, we evaluated the change of U251-MG and U87-MG human malignant glioma cells after 43 degrees C-heat shock comparing with that of 45 degrees C. First, we observed that cell growth was transiently inhibited after 43 degrees C-heat shock for 3 or 5 days, in U251-MG or U87-MG cells, respectively, which was followed by regrowth. During the period of transient growth inhibition, mild G2/M arrest was observed. However, apoptosis was observed in only 2.7% or 1.5%, of 43 degrees C-heated cells, in U251-MG or U87-MG cells, respectively. Instead, transmission electron micrography showed the formation of vacuoles, degeneration of mitochondria, and autophagosomes. Moreover, in the both cell lines, flow-cytometric analysis with acridine orange revealed the induction of acidic vesicle organelles, which was blocked by 3-methyladenine (3-MA), suggesting the involvement of autophagy. Furthermore, while 3-MA did not increase the anti-tumor effect of 43 degrees C-heat shock, bafilomycin A1, another autophagy inhibitor, did significantly enhance the effect in U251-MG cells. Taken together, mild heat shock (43 degrees C for 2 h) causes autophagy and mild G2/M arrest, but does not induce apparent apoptosis in U251-MG and U87-MG glioma cells. Inhibition of autophagy with bafilomycin A1 may increase the anti-tumor efficacy of mild heat shock against some malignant glioma cells.