Interstitial thermoradiotherapy with ferromagnetic implants for locally advanced and recurrent neoplasms

Application of a new self-regulating temperature magnetic material Fe83Zr10B7 in magnetic induction hyperthermia

INTRODUCTION

The temperature control of magnetic hyperthermia therapy mainly relies on circulating water cooling and regulating magnetic field intensity, which increases complexity in clinical applications. Using magnetic materials with appropriate Curie temperature has become an effective means to solve temperature monitoring and potentially achieve self-regulating temperature.

METHODS

A self-temperature-regulating Fe83Zr10B7 magnetic material was prepared. Based on this material, a simplified model of magnetic hyperthermia for arm tumors was established and verified using the finite- element method. The influence of magnetic field intensity and frequency on the heating power and temperature rise rate of different-sized and shaped magnetic media was studied. Additionally, factors such as the size, quantity, and spatial arrangement of the magnetic media were analyzed for their impact on the damage to tumors with different volumes and shapes.

RESULTS

Spherical shape is the most suitable for magnetic hyperthermia media, and the radius of the spherical magnetic media can be chosen according to the size of the tumor. For tumors with a radius below 10 mm, using magnetic media with a particle size of 3.5 mm is recommended. The optimal magnetic field conditions are H0 (10-12 kA/m) and f (110-120 kHz).

CONCLUSION

Based on the good magnetic properties and heating performance of the Fe83Zr10B7 magnetic material, it is feasible to use it as a magnetic medium for magnetic hyperthermia. The results of this study provide references for the selection of thermal seed size and magnetic field parameters in magnetic hyperthermia.

Characterization of Ferromagnetic Composite Implants for Tumor Bed Hyperthermia

Hyperthermia therapy (HT) is becoming a well-recognized method for the treatment of cancer when combined with radiation or chemotherapy. There are many ways to heat a tumor and the optimum approach depends on the treatment site. This study investigates a composite ferromagnetic surgical implant inserted in a tumor bed for the delivery of local HT. Heating of the implant is achieved by inductively coupling energy from an external magnetic field of sub-megahertz frequency. Implants are formed by mechanically filling a resected tumor bed with self-polymerizing plastic mass mixed with small ferromagnetic thermoseeds. Model implants were manufactured and then heated in a 35 cm diameter induction coil of our own design. Experimental results showed that implants were easily heated to temperatures that allow either traditional HT (39-45°C) or thermal ablation therapy (>50°C) in an external magnetic field with a frequency of 90 kHz and amplitude not exceeding 4 kA/m. These results agreed well with a numerical solution of combined electromagnetic and heat transfer equations solved using the finite element method.

Heating technology for malignant tumors: a review

The therapeutic application of heat is very effective in cancer treatment. Both hyperthermia, i.e., heating to 39-45 °C to induce sensitization to radiotherapy and chemotherapy, and thermal ablation, where temperatures beyond 50 °C destroy tumor cells directly are frequently applied in the clinic. Achievement of an effective treatment requires high quality heating equipment, precise thermal dosimetry, and adequate quality assurance. Several types of devices, antennas and heating or power delivery systems have been proposed and developed in recent decades. These vary considerably in technique, heating depth, ability to focus, and in the size of the heating focus. Clinically used heating techniques involve electromagnetic and ultrasonic heating, hyperthermic perfusion and conductive heating. Depending on clinical objectives and available technology, thermal therapies can be subdivided into three broad categories: local, locoregional, or whole body heating. Clinically used local heating techniques include interstitial hyperthermia and ablation, high intensity focused ultrasound (HIFU), scanned focused ultrasound (SFUS), electroporation, nanoparticle heating, intraluminal heating and superficial heating. Locoregional heating techniques include phased array systems, capacitive systems and isolated perfusion. Whole body techniques focus on prevention of heat loss supplemented with energy deposition in the body, e.g., by infrared radiation. This review presents an overview of clinical hyperthermia and ablation devices used for local, locoregional, and whole body therapy. Proven and experimental clinical applications of thermal ablation and hyperthermia are listed. Methods for temperature measurement and the role of treatment planning to control treatments are discussed briefly, as well as future perspectives for heating technology for the treatment of tumors.

Magnetic Hyperthermia as an adjuvant cancer therapy in combination with radiotherapy versus radiotherapy alone for recurrent/progressive glioblastoma: a systematic review

INTRODUCTION

Hyperthermia therapy (HT) is a recognized treatment modality, that can sensitize tumors to the effects of radiotherapy (RT) and chemotherapy by heating up tumor cells to 40-45 °C. The advantages of noninvasive inductive magnetic hyperthermia (MH) over RT or chemotherapy in the treatment of recurrent/progressive glioma have been confirmed by several clinical trials. Thus, here we have conducted a systematic review to provide a concise, albeit brief, account of the currently available literature regarding this topic.

METHODS

Five databases, PubMed/Medline, Embace, Ovid, WOS, and Scopus, were investigated to identify clinical studies comparing overall survival (OS) following RT/chemotherapy versus RT/chemotherapy + MH.

RESULTS

Eleven articles were selected for this systematic review, including reports on 227 glioma patients who met the study inclusion criteria. The papers included in this review comprised nine pilot clinical trials, one non-randomized clinical trial, and one retrospective investigation. As the clinical trials suggested, MH improved OS in primary glioblastoma (GBM), however, in the case of recurrent glioblastoma, no significant change in OS was reported. All 11 studies ascertained that no major side effects were observed during MH therapy.

CONCLUSION

Our systematic review indicates that MH therapy as an adjuvant for RT could result in improved survival, compared to the therapeutic outcomes achieved with RT alone in GBM, especially by intratumoral injection of magnetic nanoparticles. However, heterogeneity in the methodology of the most well-known studies, and differences in the study design may significantly limit the extent to which conclusions can be drawn. Thus, further investigations are required to shed more light on the efficacy of MH therapy as an adjuvant treatment modality in GBM.

Feasibility of removable balloon implant for simultaneous magnetic nanoparticle heating and HDR brachytherapy of brain tumor resection cavities

AIM

Hyperthermia (HT) has been shown to improve clinical response to radiation therapy (RT) for cancer. Synergism is dramatically enhanced if HT and RT are combined simultaneously, but appropriate technology to apply treatments together does not exist. This study investigates the feasibility of delivering HT with RT to a 5-10mm annular rim of at-risk tissue around a tumor resection cavity using a temporary thermobrachytherapy (TBT) balloon implant.

METHODS

A balloon catheter was designed to deliver radiation from High Dose Rate (HDR) brachytherapy concurrent with HT delivered by filling the balloon with magnetic nanoparticles (MNP) and immersing it in a radiofrequency magnetic field. Temperature distributions in brain around the TBT balloon were simulated with temperature dependent brain blood perfusion using numerical modeling. A magnetic induction system was constructed and used to produce rapid heating (>0.2°C/s) of MNP-filled balloons in brain tissue-equivalent phantoms by absorbing 0.5 W/ml from a 5.7 kA/m field at 133 kHz.

RESULTS

Simulated treatment plans demonstrate the ability to heat at-risk tissue around a brain tumor resection cavity between 40-48°C for 2-5cm diameter balloons. Experimental thermal dosimetry verifies the expected rapid and spherically symmetric heating of brain phantom around the MNP-filled balloon at a magnetic field strength that has proven safe in previous clinical studies.

CONCLUSIONS

These preclinical results demonstrate the feasibility of using a TBT balloon to deliver heat simultaneously with HDR brachytherapy to tumor bed around a brain tumor resection cavity, with significantly improved uniformity of heating over previous multi-catheter interstitial approaches. Considered along with results of previous clinical thermobrachytherapy trials, this new capability is expected to improve both survival and quality of life in patients with glioblastoma multiforme.

Quality assurance guidelines for interstitial hyperthermia

Quality assurance (QA) guidelines are essential to provide uniform execution of clinical hyperthermia treatments and trials. This document outlines the clinical and technical consequences of the specific properties of interstitial heat delivery and specifies recommendations for hyperthermia administration with interstitial techniques. Interstitial hyperthermia aims at tumor temperatures in the 40-44 °C range as an adjunct to radiation or chemotherapy. The clinical part of this document imparts specific clinical experience of interstitial heat delivery to various tumor sites as well as recommended interstitial hyperthermia workflow and procedures. The second part describes technical requirements for quality assurance of current interstitial heating equipment including electromagnetic (radiative and capacitive) and ultrasound heating techniques. Detailed instructions are provided on characterization and documentation of the performance of interstitial hyperthermia applicators to achieve reproducible hyperthermia treatments of uniform high quality. Output power and consequent temperature rise are the key parameters for characterization of applicator performance in these QA guidelines. These characteristics determine the specific maximum tumor size and depth that can be heated adequately. The guidelines were developed by the ESHO Technical Committee with participation of senior STM members and members of the Atzelsberg Circle.

Development of custom RF coils for use in a small animal platform for magnetic resonance-guided focused ultrasound hyperthermia compatible with a clinical MRI scanner

Three different magnetic resonance imaging (MRI) coils were developed and assessed for use with an experimental platform designed to generate hyperthermia in mice using magnetic resonance-guided focused ultrasound (MRgFUS). An ergonomic animal treatment bed was integrated with MRI coils. Three different coil designs optimized for small targets were tested, and performance in targeting and conducting accurate temperature imaging was evaluated. Two transmit/receive surface coils of different diameters (4 and 7 cm) and a transmit-only/receive-only (TORO) coil were used. A software platform was developed to provide real-time targeting and temperature maps and to deliver controlled ultrasound exposure. MR thermometry was conducted on different targets, including fresh chicken breasts and mouse cadavers. Multiple experiments were performed in which tissues were targeted with high reproducibility. The TORO coil was the most resilient to temperature drift, resulting in an increase in the calculated temperature of 0.29 ± 0.12 °C, compared to 1.27 ± 0.13 °C and 0.47 ± 0.04 °C for the medium and small coils, respectively. Controlled closed-loop hyperthermia exposure was successfully performed with all three coils. Considering all assessments, the TORO coil exhibited the best overall performance for thermometry acquisition when accounting for stability, precision, temperature spread and resilience to temperature drift. B₁ maps of the three coils confirmed that the TORO coil exhibited the most homogeneous B₁ field, which explained the improved thermometry performance. The use of coils specifically designed for small targets within the proposed experimental platform allowed accurate thermometry during hyperthermia.

Practical considerations for maximizing heat production in a novel thermobrachytherapy seed prototype

PURPOSE

A combination of hyperthermia and radiation in the treatment of cancer has been proven to provide better tumor control than radiation administered as a monomodality, without an increase in complications or serious toxicities. Moreover, concurrent administration of hyperthermia and radiation displays synergistic enhancement, resulting in greater tumor cell killing than hyperthermia and radiation delivered separately. The authors have designed a new thermobrachytherapy (TB) seed, which serves as a source of both radiation and heat for concurrent brachytherapy and hyperthermia treatments when implanted in solid tumors. This innovative seed, similar in size and geometry to conventional seeds, will have self-regulating thermal properties.

METHODS

The new seed's geometry is based on the standard BEST Model 2301(125)I seed, resulting in very similar dosimetric properties. The TB seed generates heat when placed in an oscillating magnetic field via induction heating of a ferromagnetic Ni-Cu alloy core that replaces the tungsten radiographic marker of the standard Model 2301. The alloy composition is selected to undergo a Curie transition near 50 °C, drastically decreasing power production at higher temperatures and providing for temperature self-regulation. Here, the authors present experimental studies of the magnetic properties of Ni-Cu alloy material, the visibility of TB seeds in radiographic imaging, and the ability of seed prototypes to uniformly heat tissue to a desirable temperature. Moreover, analyses are presented of magnetic shielding and thermal expansion of the TB seed, as well as matching of radiation dose to temperature distributions for a short interseed distance in a given treatment volume.

RESULTS

Annealing the Ni-Cu alloy has a significant effect on its magnetization properties, increasing the sharpness of the Curie transition. The TB seed preserves the radiographic properties of the BEST 2301 seed in both plain x rays and CT images, and a preliminary experiment demonstrates thermal self-regulation and adequate heating of a tissue-mimicking phantom by seed prototypes. The effect of self-shielding of the seed against the external magnetic field is small, and only minor thermal stress is induced in heating of the seeds from room temperature to well above the seed operating temperature. With proper selection of magnetic field parameters, the thermal dose distribution of an arrangement of TB and hyperthermia-only seeds may be made to match with its radiation dose distribution.

CONCLUSIONS

The presented analyses address several practical considerations for manufacturing of the proposed TB seeds and identify critical issues for the prototype implementation. The authors' preliminary experiments demonstrate close agreement with the modeling results, confirming the feasibility of combining sources of heat and radiation into a single thermobrachytherapy seed.

Long duration mild temperature hyperthermia and brachytherapy

Combining long duration mild temperature hyperthermia (LDMH) and low dose-rate (LDR) brachytherapy to enhance therapeutic killing of cancer cells was proposed many years ago. The cellular and tumour research that supports this hypothesis is presented in this review. Research describing LDMH interaction with pulsed brachytherapy and high dose-rate brachytherapy using clinically relevant parameters are compared with LDMH/LDR brachytherapy. The mechanism by which LDMH sensitizes LDR has been established as the inhibition of sublethal damage repair. The molecular mechanisms have been shown to involve DNA repair enzymes, but the exact nature of these processes is still under investigation. The relative differences between LDMH interactions with human and rodent cells are presented to help in the understanding of possible roles of LDMH in clinical application. The role of LDMH in modifying tumour blood flow and its possible role in LDR sensitization of tumours is also presented. The positive aspects of LDMH-brachytherapy for clinical application are sixfold; (1) the thermal goals (temperature, time and volume) are achievable with currently available technology, (2) the hyperthermia by itself has no detectable toxic effects, (3) thermotolerance appears to play a minor if any role in radiation sensitization, (4) TER of around 2 can be expected, (5) hypoxic fraction may be decreased due to blood flow modification and (6) simultaneous chemotherapy may also be sensitized. Combined LDMH and brachytherapy is a cancer therapy that has established biological rationale and sufficient technical and clinical advancements to be appropriately applied. This modality is ripe for clinical testing.

Treatment planning of brain implants using vascular information and a new template technique

A new template technique has been developed for implanting hyperthermia catheters in the treatment of brain tumors. The technique utilizes an imaging template and a drill template which can be rigidly secured to the head with three skull screws. The anatomic and vascular information needed for hyperthermia treatment planning may be assessed with three-dimensional magnetic resonance (MR) imaging and angiography acquisitions which use a surface coil. In the companioning treatment planning system the catheter positions and lengths and the electrodes in the catheter can be interactively manipulated relative to the anatomy and vasculature. The visualization of the blood vessels relative to the template allows the minimization of the risk on intracranial hemorrhages. This template technique is useful for any brain tumor implants, especially when a large number of catheters are involved. A phantom test has shown that this procedure has an accuracy in the order of 1 mm provided that the MR-related geometry distortions are minimized.

Orientated thermotherapy of ferromagnetic thermoseed in hepatic tumors

AIM: To study the thermotherapeutic effects of implanted ferromagnetic thermoseeds in high frequency electromagnetic field in hepatic tumors.

METHODS: The ferromagnetic thermoseeds made of nickel-copper alloy, which has a lower Curie temperature, were implanted into hepatic tumors of mice. The high frequency electromagnetic field was then applied in vitro to make the ferromagnetic thermoseeds produce the hyperthermia. Before and after thermotherapy, the tumor size, pathologic alteration and animal survival period were assessed.

RESULTS: The temperature at the central area of the tumor could be heated up to 50 °C. Most of tumors in mice disappeared with a large amount of tumor necrosis. The survival period of mice was prolonged.

CONCLUSION: This thermotherapy is beneficial to directional selection and temperature control for treatment of hepatic tumors.

Dose uniformity of ferromagnetic seed implants in tissue with discrete vasculature: a numerical study on the impact of seed characteristics and implantation techniques

The results from simulations with a new three-dimensional treatment planning system for interstitial hyperthermia with ferromagnetic seeds are presented in this study. The thermal model incorporates discrete vessel structures as well as a heat sink and enhanced thermal conductivity. Both the discrete vessels and the ferroseeds are described parametrically in separate calculation spaces. This parametric description has the advantage of an arbitrary orientation of the structures within the tissue grid, easy manipulation of the structures and independence from the resolution of the tissue voxels (tissue calculation space). The power absorption of the self-regulating seeds is according to empirical data. The thermal effects of an unlimited number of thin layers surrounding the seed (coatings, catheters) can be modelled. The initial calculations have been performed for an array of 12 identical ferromagnetic seeds in a tissue volume with a computer generated artificial vessel network spanning four vessel generations in both the arterial and venous tree. The heterogeneously distributed large isolated vessels impair the temperature distribution significantly, indicating the limited accuracy of continuum models. Simulations with different types of ferromagnetic seeds have confirmed that the efforts of previous studies to optimize the self-regulating temperature control and the implantation techniques of the ferroseeds will improve the homogeneity of the temperature distribution in the target volume. Multifilament seeds implanted in brachytherapy needles and tubular seeds appear to be the most favourable configurations. The division of long seeds into shorter segments with the appropriate Curie temperature will further improve the homogeneity of the temperature distribution without increasing the average temperature in the volume of interest. Given the proper thermal tissue data, the model presented in this study will prove to be a useful tool in making choices for the implant geometry, seed spacing and Curie temperature.

A ferrite core/metallic sheath thermoseed for interstitial thermal therapies

An alternative form of ferromagnetic seed for thermal therapy has been developed following Matsuki, Murakami, and their colleagues [1]-[4]. A nearly lossless ceramic ferrite core (FC) is surrounded by an electrically conductive sheath. The FC has a high relative intrinsic permeability, typically 3000 at low magnetic field strengths, and a sharp transition from the ferrimagnetic state to the nonmagnetic state. The sheath is either a metallic tube or coating on the core. When this composite seed is excited with a radiofrequency magnetic field, large eddy currents are induced in the metallic sheath (MS) due to the concentrated magnetic flux in the core leading to Joule heating. Advantages of this configuration are that this ferrite core/metallic sheath (FC/MS) thermoseed has high power absorption efficiency and a sharp transition compared to ferromagnetic alloy systems; means of optimizing efficiency are apparent from simple expressions; the outer sheath can be of any biocompatible metal; the production method for the ferrites leads to large quantities of seeds with reproducible properties. The FC/MS configuration solves many of the technical problems that have hindered the clinical implementation of thermally regulating ferromagnetic implants for thermal therapies.

Three-dimensional temperature control of palladium-nickel thermoseeds: a computer aided and experimental evaluation

The capability of self-regulating thermoseeds to compensate for nonuniform cooling along their longitudinal axis has been investigated in this study. For this purpose a quasi three-dimensional computer model has been developed. Calculations of the temperature profile in tissue with nonuniform heat loss demonstrated a clear improvement in the longitudinal temperature control of PdNi seeds compared to constant power seeds. Further, two strategies for improved control of nonuniform cooling along the longitudinal axis of ferromagnetic seeds have been investigated: (1) application of a 'normal' undivided seed; and (2) division of a long seed in smaller segments of which each segment is able to respond more directly to local variations in the temperature distribution. Calculations with the quasi three-dimensional model showed that the loose segments do respond more directly to their close proximity. However, the equilibrium temperature of a segment in an area with high local blood flow will be relatively low due the limited heat production of PdNi thermoseeds. In the undivided seeds the high thermal conductivity of PdNi causes some levelling of the longitudinal temperature gradient in the seed. In addition, calorimetric experiments have shown that the heat production of a segmented seed is less effective because of a demagnetizing field. Also, the absence of PdNi between the segments reduces the heat production of the seed.

The effect of catheters and coatings on the performance of palladium-nickel thermoseeds: evaluation and design of implantation techniques

In the development of materials for self-regulating thermoseeds much effort is put in improvement of the self-regulating temperature control mechanism of the seeds. The catheters and coatings which are needed to implant the seeds or to guarantee biocompatibility, generally impair the optimized performance of the ferromagnetic seeds. The influence of various coatings on the performance of PdNi seeds has been investigated by means of one-dimensional modelling and calorimetric experiments. Implantation using thin walled catheters is acceptable provided that the catheters are filled with water to assure good thermal coupling. Air layers inside catheters should be avoided as they reduce the sharp gradient of the heat production at the Curie temperature significantly. An alternative for the application of catheters is to insert the seeds into metallic needles. The effect of shielding by the metal needle can be minimized by driving the seed into its saturated state using a high magnetic field strength. The thermal interaction between the seed and surrounding tissue can also be enhanced by placing PdNi, e.g. tubular, on the outside of the catheter or brachytherapy needle. An additional advantage of this new design is an increase in the heat production and the quality of temperature control due to an increase in the amount of PdNi. For permanent implantation seeds can be coated with an inert metal, ceramics or plastic. The performance of the seeds is not affected by any of the coatings if certain conditions are met. For plastic coatings the thickness of the coating has to be very thin, preferably < or = 20 microns, to avoid thermal isolation.

Practical induction heating coil designs for clinical hyperthermia with ferromagnetic implants

Interstitial techniques for hyperthermia therapy of cancer continue to evolve in response to requirements for better localization and control over heating of deep seated tissues. Magnetic induction heating of ferromagnetic implants is one of several available techniques for producing interstitial hyperthermia, using thermal conduction to redistribute heat within an array of controlled temperature "hot sources." This report describes seven induction heating coil designs that can be used for producing strong magnetic fields around ferromagnetic seed implants located in different sites in the body. The effect of coil design on the extent and uniformity of the magnetic field is characterized, and appropriate electrostatic shield designs for minimizing electric field coupling to the patient are described. Advantages and disadvantages of each coil type are discussed in terms of the radiated fields, coil efficiency, and ease of use, and appropriate applications are given for each design. This armamentarium of induction coils provides the ability to customize magnetic field distributions for improved coupling of energy into ferromagnetic implant arrays located at any depth or orientation in the body. Proper selection of heating coil configuration should simplify patient setup, improve the safety of patient treatments, and pave the way for future applications of interstitial heating in sites that were previously untreatable.