Physiological mechanisms in hyperthermia: a review

Hyperthermia and radiotherapy: physiological basis for a synergistic effect

In cancer treatment, mild hyperthermia (HT) represents an old, but recently revived opportunity to increase the efficacy of radiotherapy (RT) without increasing side effects, thereby widening the therapeutic window. HT disrupts cellular homeostasis by acting on multiple targets, and its combination with RT produces synergistic antitumoral effects on specific pathophysiological mechanisms, associated to DNA damage and repair, hypoxia, stemness and immunostimulation. HT is furthermore associated to direct tumor cell kill, particularly in higher temperature levels. A phenomenon of temporary resistance to heat, known as thermotolerance, follows each HT session. Cancer treatment requires innovative concepts and combinations to be tested but, for a meaningful development of clinical trials, the understanding of the underlying mechanisms of the tested modalities is essential. In this mini-review, we aimed to describe the synergistic effects of the combination of HT with RT as well as the phenomena of thermal shock and thermotolerance, in order to stimulate clinicians in new, clinically relevant concepts and combinations, which become particularly relevant in the era of technological advents in both modalities but also cancer immunotherapy.

Estimation of the injection criteria for magnetic hyperthermia therapy based on tumor morphology

Intratumoral multi-injection strategy enhances the efficacy of magnetic nanoparticle hyperthermia therapy (MNPH). In this study, criteria for the selection of injections and their location depending on the tumor shape/geometry are developed. The developed strategy is based on the thermal dosimetry results of different invasive 3D tumor models during MNPH simulation. MNPH simulations are conducted on physical tumor tissue models encased within healthy tissue. The tumor shapes are geometrically divided into a central tumor region containing maximum tumor volume and a peripheral tumor portion protruding in any random direction. The concepts of core and invasive radius are used to geometrically divide the tumor volume. Primary & secondary injections are used to inject MNP fluid into these respective tumor regions based on the invasiveness of the tumor. The optimization strategy is devised based on the zone of influence of primary & secondary injection. Results indicate that the zone of influence of secondary injection lies between 0.7 and 0.8 times the radial distance between the center of the tumor core and branch node point (extreme far endpoint on the invasive tumor surface). Additionally, the multi-injection strategy is more effective when the protrusion volume exceeds10%of the total volume. The proposed algorithm is used to devise multi-injection strategies for arbitrarily shaped tumors and will assist in pre-planning magnetic nanoparticle hyperthermia therapy.

Piezo-enhanced near infrared photocatalytic nanoheterojunction integrated injectable biopolymer hydrogel for anti-osteosarcoma and osteogenesis combination therapy

Preventing local tumor recurrence while promoting bone tissue regeneration is an urgent need for osteosarcoma treatment. However, the therapeutic efficacy of traditional photosensitizers is limited, and they lack the ability to regenerate bone. Here, a piezo-photo nanoheterostructure is developed based on ultrasmall bismuth/strontium titanate nanocubes (denoted as Bi/SrTiO3), which achieve piezoelectric field-driven fast charge separation coupling with surface plasmon resonance to efficiently generate reactive oxygen species. These hybrid nanotherapeutics are integrated into injectable biopolymer hydrogels, which exhibit outstanding anticancer effects under the combined irradiation of NIR and ultrasound. In vivo studies using patient-derived xenograft models and tibial osteosarcoma models demonstrate that the hydrogels achieve tumor suppression with efficacy rates of 98.6 % and 67.6 % in the respective models. Furthermore, the hydrogel had good filling and retention capabilities in the bone defect region, which exerted bone repair therapeutic efficacy by polarizing and conveying electrical stimuli to the cells under mild ultrasound radiation. This study provides a comprehensive and clinically feasible strategy for the overall treatment and tissue regeneration of osteosarcoma.

Evaluation of Thermal Properties of Ferromagnetic Core for Treatment of Solid Tumors by Electromagnetic Induction Hyperthermia

Background

Electromagnetic induction hyperthermia is a promising method to treat the deep-seated tumors such as brain and prostatic tumors. This technique is performed using the induction of electromagnetic waves in the ferromagnetic cores implanted at the solid tumor.

Objective

This study aims at determining the conditions of the optimal thermal distribution in the different frequencies before performing the in vitro cellular study.

Material and Methods

In this experimental study, the i-Cu alloy (70.4-29.6; wt%) was prepared and characterized and then the parameters, affecting the amount of induction heating in the ferromagnetic core, were investigated. Self-regulating cores in 1, 3, 6, and 9 arrangements in the water phantom with a volume of 2 cm3 were used as a replacement for solid tumor.

Results

Inductively Coupled Plasma (ICP) analysis and Energy Dispersive X-ray Spectroscopy (EDS) show the uniformity of the alloy after 4 times remeling by vacuum arc remelting furnace. The Vibrating Sample Magnetometer (VSM) shows that the Curie temperature (TC) of the ferromagnetic core is less than 50 °C. Temperature profile with a frequency of 100-400 kHz for 30 min, was extracted by infrared imaging camera, indicating the increase temperature in the range of 42 °C to 46 °C.

Conclusion

The optimum conditions with used hyperthermia system are supplied in the frequency of 100 kHz, 200 kHz and 400 kHz with 6, 3 and 1 seeds, respectively. It is also possible to induce a temperature up to 50 °C by increasing the number of seeds at a constant frequency and power, or by increasing the applied frequency at a constant number of seeds.

Photoresponsive Inorganic Nanomaterials in Oncology

The diagnosis and treatment of cancer are continuously evolving in search of more efficient, safe, and personalized approaches. Therapies based on nanoparticles or physical stimuli-responsive substances have shown great potential to overcome the inherent shortcomings of conventional cancer therapies. In fact, nanoparticles may increase the half-life of chemotherapeutic agents or promote the targeting in cancer tissues while physical stimuli-responsive substances are more effective and safer with respect to traditional chemotherapeutic agents because of the possibility to be switched on only when needed. These 2 approaches can be combined by exploiting the ability of some inorganic nanomaterials to be activated by light, ultrasounds, magnetic fields, or ionizing radiations. Albeit the development of stimuli-responsive materials is still at the early stages, research in this field is rapidly growing since they have important advantages with respect to organic nanoparticles or molecular substances, like higher stability, and higher efficiency in converting the stimulus in heat or, in some cases, reactive oxygen species. On the other hand, the translation process is slowed down by issues related to safety and quality of the formulations. This literature review summarizes the current advancements in this research field, analysing the most promising materials and applications.

Safety, feasibility, and application of intraperitoneal gas-based hyperthermia beyond 43°C in the treatment of peritoneal metastasis: An in-vivo pilot study

Background

43°Celsius (C) is currently the highest temperature used in the treatment of peritoneal metastasis (PM). Despite sufficient data on water- based hyperthermic solutions in PM treatment, there is currently no information on gas-based hyperthermia extending beyond 43°C. This study is the first to provide in-vivo data on different organ systems during and after intraperitoneal gas-based hyperthermia beyond 43°C. The aim of this study is to explore in-vivo feasibility, safety, and efficacy of this novel concept from a biological perspective.

Methods

For this study, three swine were subjected to laparoscopy and subsequent gas-based intraperitoneal hyperthermia at 48°, 49° and 50°C under a high-flow air stream. Intraoperative data from multiple temperature sensors were analysed. Additionally, intraoperative anaesthesiologic and gasometrical data was analysed. Postoperatively, swine were monitored for one week and laboratory work-up was performed on postoperative days 1, 3 and 7.

Results

During gas-based intraperitoneal hyperthermia, anesthesiologic parameters did not exhibit critical values. No intra- or postoperative complications were observed. Distinct temperature measurements on the skin, cystohepatic triangle and esophagus did not display any temperature increase. Postoperative laboratory workup did not show any changes in hemoglobin, white blood cell count, platelets, or kidney function.

Discussion

Based on our data, there are no safety concerns for the application of gas-based hyperthermia between 48 - 50°C. In fact, no critical systemic temperature increase was observed. With respect to possible limitations, further in-vivo studies are required to evaluate whether gas-based intraperitoneal hyperthermia may be a therapeutic option for PM patients.

In-vivo thermodynamic exploration of gas-based intraperitoneal hyperthermia

Background

While hyperthermic intraperitoneal (i.p) applications are highly efficient in treating peritoneal metastases (PM), they are currently limited to temperatures of 41 – 43° Celsius (C). First data on gas-based i.p. hyperthermia is promising, as this novel method allows a significant temperature rise in superficial peritoneal layers without increasing core temperatures. Until now, key mechanisms of this novel tool, e.g. thermodynamic energy transfer, have not been investigated. This study aims to explore the volume of thermodynamic energy transfer during gas-based i.p. hyperthermia at 48-50°C and its peritoneal effects.

Methods

For this study, three swine were subjected to gas-based i.p. hyperthermia at varying temperatures (48°, 49° and 50°C) in a diagnostic laparoscopy setting with a high-flow air stream. Temperatures of the i.p. cavity, in- and outflow airstream at the trocar were measured and the thermodynamic energy transfer was calculated. Tissue samples were collected on postoperative day 7 for histopathologic analyses.

Results

According to our data, temperatures within the intraabdominal cavity and at the outflow site remain relatively stable at < 40°C. An increase in thermodynamic energy transfer is observed with increasing applied temperatures. Gas-based i.p. hyperthermia induced capillary coagulation and white blood cell infiltration within peritoneal layers.

Conclusions

Gas-based i.p. hyperthermia is an innovative approach which enables the i.p. delivery of specific amounts of thermodynamic energy. Following this procedure, our data indicate remarkable histologic changes on the superficial peritoneal layer most likely attributable to the applied thermodynamic energy. Further studies are required to investigate how these findings can be applied in PM management.

Comparison of different energy response for lipolysis using a 1,060-nm laser: An animal study of three pigs

BACKGROUND

Non-invasive body-sculpting procedures are becoming increasingly popular. The application of 1,060 nm of laser energy transcutaneously to hyperthermically induce the disruption of fat cells in the abdomen is a type of non-invasive procedure.

AIMS

The purpose of this study was to compare the treatment results from two parameters of the same system, each with different energy output levels, in an in vivo porcine model to determine the most effective application.

METHODS

Female pigs (n = 3) were used in this study. We examined the effects of the treatment using photography, ultrasonography, gross and microscopic pathology, and histological examination in order to determine the mechanism of action, efficacy, and safety of the procedure. Blood chemistry analysis was performed before each session to check lipid levels and to monitor for any adverse changes in markers that may indicate liver damage. Biopsies were taken and routinely processed with hematoxylin and eosin and Oil Red O stains to examine for tissue damage at baseline and after each treatment. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) assays were performed to check for apoptotic-related DNA damage.

RESULTS

Ultrasonic imaging of the same area before and after the application of 1,060 nm of laser energy at outputs of 0.9 and 1.4 W/cm² showed that the density of the fat layer changed immediately after irradiation due to the transient heat transfer in the fat layer. Preclinical evaluation was performed to obtain comparison data on the safety and efficacy of subcutaneous fat reduction after applying the different energy outputs of 0.9 and 1.4 W/cm² .

CONCLUSION

Based on our findings, we suggest that long-term histologic changes through the use of these devices suggest a comparative effectiveness of the treatment energy.

Integrating Loco-Regional Hyperthermia Into the Current Oncology Practice: SWOT and TOWS Analyses

Moderate hyperthermia at temperatures between 40 and 44°C is a multifaceted therapeutic modality. It is a potent radiosensitizer, interacts favorably with a host of chemotherapeutic agents, and, in combination with radiotherapy, enforces immunomodulation akin to “in situ tumor vaccination.” By sensitizing hypoxic tumor cells and inhibiting repair of radiotherapy-induced DNA damage, the properties of hyperthermia delivered together with photons might provide a tumor-selective therapeutic advantage analogous to high linear energy transfer (LET) neutrons, but with less normal tissue toxicity. Furthermore, the high LET attributes of hyperthermia thermoradiobiologically are likely to enhance low LET protons; thus, proton thermoradiotherapy would mimic ¹²C ion therapy. Hyperthermia with radiotherapy and/or chemotherapy substantially improves therapeutic outcomes without enhancing normal tissue morbidities, yielding level I evidence reported in several randomized clinical trials, systematic reviews, and meta-analyses for various tumor sites. Technological advancements in hyperthermia delivery, advancements in hyperthermia treatment planning, online invasive and non-invasive MR-guided thermometry, and adherence to quality assurance guidelines have ensured safe and effective delivery of hyperthermia to the target region. Novel biological modeling permits integration of hyperthermia and radiotherapy treatment plans. Further, hyperthermia along with immune checkpoint inhibitors and DNA damage repair inhibitors could further augment the therapeutic efficacy resulting in synthetic lethality. Additionally, hyperthermia induced by magnetic nanoparticles coupled to selective payloads, namely, tumor-specific radiotheranostics (for both tumor imaging and radionuclide therapy), chemotherapeutic drugs, immunotherapeutic agents, and gene silencing, could provide a comprehensive tumor-specific theranostic modality akin to “magic (nano)bullets.” To get a realistic overview of the strength (S), weakness (W), opportunities (O), and threats (T) of hyperthermia, a SWOT analysis has been undertaken. Additionally, a TOWS analysis categorizes future strategies to facilitate further integration of hyperthermia with the current treatment modalities. These could gainfully accomplish a safe, versatile, and cost-effective enhancement of the existing therapeutic armamentarium to improve outcomes in clinical oncology.

Hyperthermia with photon radiotherapy is thermoradiobiologically analogous to neutrons for tumors without enhanced normal tissue toxicity

The depth dose profiles of photons mirror those of fast neutrons. However, in contrast to the high linear energy transfer (LET) characteristics of neutrons; photons exhibit low LET features. Hyperthermia (HT) inhibits the repair of radiation-induced DNA damage and is cytotoxic to the radioresistant hypoxic tumor cells. Thus, thermoradiobiologically, HT simulates high LET radiation with photons. At temperatures of 39-45 °C, the physiological vasodilation allows rapid heat dissipation from normal tissues. On the contrary, the chaotic and relatively rigid tumor vasculature results in heat retention leading to higher intratumoural temperatures. Consequently, the high LET attributes of HT with photon radiations are mostly limited to the confines of the heated tumor while the normothermic normal tissues would be irradiated with low LET photons. HT thereby augments photon therapy by conferring therapeutic advantages of high LET radiations to the tumors akin to neutrons, while the 'heat-sink' effect spares the normal tissues from thermal radiosensitization. Thus, photon thermoradiotherapy imparts radiobiological advantages selectively to tumors analogous to neutrons without exaggerating normal tissue morbidities. The later has been the major concern with clinical fast neutron beam therapy. Outcomes reported from several clinical trials in diverse tumor sites add testimony to the enhanced therapeutic efficacy of photon thermoradiotherapy.

Ultrasound Hyperthermia Technology for Radiosensitization

Hyperthermia therapy (HT) raises tissue temperature to 40-45°C for up to 60 min. Hyperthermia is one of the most potent sensitizers of radiation therapy (RT). Ultrasound-mediated HT for radiosensitization has been used clinically since the 1960s. Recently, magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU), which has been approved by the United States Food and Drug Administration for thermal ablation therapy, has been adapted for HT. With emerging clinical trials using MRgHIFU HT for radiosensitization, there is a pressing need to review the ultrasound HT technology. The objective of this review is to overview existing HT technology, summarize available ultrasound HT devices, evaluate clinical studies combining ultrasound HT with RT and discuss challenges and future directions.

Modeling Heat Transfer in Tumors: A Review of Thermal Therapies

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

Plasmonic carbon nanohybrids for repetitive and highly localized photothermal cancer therapy

Integrating metallic and non-metallic platform for cancer nanomedicine is a challenging task and bringing together multi-functionality of two interfaces is a major hurdle for biomaterial design. Herein, NIR light responsive advanced hybrid plasmonic carbon nanomaterials are synthesized, and their properties toward repetitive and highly localized photothermal cancer therapy are well understood. Graphene oxide nanosheets having thickness of ∼2 nm are synthesized using modified Hummers' method, thereafter functionalized with biodegradable NIR light responsive gold deposited plasmonic polylactic-co-glycolic acid nanoshells (AuPLGA NS, tuned at 808 nm) and NIR dye (IR780) to examine their repetitive and localized therapeutic efficacy as well resulting side effects to nearby healthy cells. It is observed that AuPLGA NS decorated graphene oxide nanosheets (GO-AuPLGA) and IR780 loaded graphene oxide nanosheets (GO-IR780) are capable in standalone complete photothermal ablation of cancer cells within 4 min. of 808 nm NIR laser irradiation and also without the aid of any anticancer drugs. However, GO-AuPLGA having the potential for repetitive photothermal treatment of a big tumor, ablate the cancer cells in highly localized fashion, without having side effects on neighboring healthy cells.

Role of Hypoxia in Photodynamic Therapy of Tumors

The photodynamic therapy of tumors is based on a photosensitization reaction that produces oxygen-derived cytotoxic species. The availability of oxygen is therefore a necessary condition to obtain the desired effect. However, most tumors develop regions that have outgrown their vascular supply, and therefore present severe hypoxia. In many hypoxic, yet viable areas, oxygen partial pressures almost two orders of magnitude lower that in normal tissues have been measured by other authors. It is here suggested that hypoxic cells are resistant to the therapy and hence are a source of postirradiation recurrence of the tumors. Methods are reviewed and discussed that can be used to: (a) improve the tumor oxygenation status prior to, or during irradiation; (b) destroy hypoxic cells; and, (c) allow the reoxygenation of the tumor by using fractionated irradiation protocols which increase tumor photosensitivity. Hyperthermia, a therapy to which hypoxic cells are particularly sensitive, is discussed. Cellular and vascular parameters that should be considered when discussing the synergism between hyperthermia and photodynamic therapy are listed. The new research field of hypoxia mapping by nondestructive, noninvasive, imaging techniques is briefly discussed.

Enzyme Degradable Hyperbranched Polyphosphoester Micellar Nanomedicines for NIR Imaging-Guided Chemo-Photothermal Therapy of Drug-Resistant Cancers

Multidrug resistance (MDR) is the major cause for chemotherapy failure, which constitutes a formidable challenge in the field of cancer therapy. The synergistic chemo-photothermal treatment has been reported to be a potential strategy to overcome MDR. In this work, rationally designed enzyme-degradable, hyperbranched polyphosphoester nanomedicines were developed for reversing MDR via the codelivery of doxorubicin and IR-780 (hPPE_DOX&IR) as combined chemo-photothermal therapy. The amphiphilic hyperbranched polyphosphoesters with phosphate bond as the branching point were synthesized via a simple but robust one-step polycondensation reaction. The self-assembled hPPE_DOX&IR exhibited good serum stability, sustained release, preferable tumor accumulation, and enhanced drug influx of doxorubicin in resistant MCF-7/ADR cells. Moreover, the degradation of hPPE_DOX&IR was accelerated in the presence of alkaline phosphatase, which was overexpressed in various cancers, resulting in the fast release of encapsulated doxorubicin. The enzyme-degradable polymer generated synergistic chemo-photothermal cytotoxicity against MCF-7/ADR cells and, thus, the efficient ablation of DOX-resistant tumor without regrowth. This delivery system may open a new avenue for codelivery of chemo- and photothermal therapeutics for MDR tumor therapy.

Efficacy of Combined Regional Inductive Moderate Hyperthermia and Chemotherapy in Patients With Multiple Liver Metastases From Breast Cancer

PURPOSE

Regional inductive moderate hyperthermia in combination with chemotherapy can improve the therapeutic efficacy in patients with breast cancer with multiple liver metastases.

METHODS

The study included 103 patients with breast cancer with multiple liver metastases: 53 patients (main group) who received a combined chemotherapy (TC drug combination) and regional inductive moderate hyperthermia treatment and 50 patients (control group) who received chemotherapy (TC drug combination) alone. Regional inductive moderate hyperthermia exploited electromagnetic fields with an operating frequency of 27.17 ± 0.16 MHz and output power of 75 W. Treatment results were assessed by computed tomography and ultrasound imaging.

RESULTS

Partial regression was defined as a 30% decrease in the sum of the maximum diameters of investigated tumors. In the current study, partial regression was described in 8 (15.1%) patients assigned to the main group and 2 (4%) patients in the control ( P < .05). The process stabilization was reported in 32 (60.4%) patients receiving the combined treatment and 19 (38%) in the control ( P < .05). Equally important, tumor progression was observed in 13 (24.5%) patients representing the main group and 29 (58%) in the control. During a 30-minute treatment session, a temperature increase overlaying greater than 90% of the liver projection exposed to electromagnetic irradiation was not exceeding 40°C.

CONCLUSION

The combined regional inductive moderate hyperthermia and chemotherapy treatment increased the overall therapeutic efficacy by 33.9% (χ2 = 12.182; P < .01).

NIR light-triggered shrinkable thermoresponsive PNVCL nanoshells for cancer theranostics

NIR light-responsive gold coated shrinkable thermoresponsive nanoshells as preliminary step to ablate large and deep-seated tumors using combined chemo-photothermal therapy.

Design and cellular studies of a carbon nanotube-based delivery system for a hybrid platinum-acridine anticancer agent

A three-component drug-delivery system has been developed consisting of multi-walled carbon nanotubes (MWCNTs) coated with a non-classical platinum chemotherapeutic agent ([PtCl(NH3)2(L)]Cl (P3A1; L=N-(2-(acridin-9-ylamino)ethyl)-N-methylproprionimidamide) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-5000] (DSPE-mPEG). The optimized P3A1-MWCNTs are colloidally stable in physiological solution and deliver more P3A1 into breast cancer cells than treatment with the free drug. Furthermore, P3A1-MWCNTs are cytotoxic to several cell models of breast cancer and induce S-phase cell cycle arrest and non-apoptotic cell death in breast cancer cells. By contrast, free P3A1 induces apoptosis and allows progression to G2/M phase. Photothermal activation of P3A1-MWCNTs to generate mild hyperthermia potentiates their cytotoxicity. These findings suggest that delivery of P3A1 to cancer cells using MWCNTs as a drug carrier may be beneficial for combination cancer chemotherapy and photothermal therapy.

Non-invasive Measurement of Thermal Diffusivity Using High-Intensity Focused Ultrasound and Through-Transmission Ultrasonic Imaging

Thermal diffusivity at the site ablated by high-intensity focused ultrasound (HIFU) plays an important role in the final therapeutic outcome, as it influences the temperature's spatial and temporal distribution. Moreover, as tissue thermal diffusivity is different in tumors as compared with normal tissue, it could also potentially be used as a new source of imaging contrast. The aim of this study was to examine the feasibility of combining through-transmission ultrasonic imaging and HIFU to estimate thermal diffusivity non-invasively. The concept was initially evaluated using a computer simulation. Then it was experimentally tested on phantoms made of agar and ex vivo porcine fat. A computerized imaging system combined with a HIFU system was used to heat the phantoms to temperatures below 42°C to avoid irreversible damage. Through-transmission scanning provided the time-of-flight values in a region of interest during its cooling process. The time-of-flight values were consequently converted into mean values of speed of sound. Using the speed-of-sound profiles along with the developed model, we estimated the changes in temperature profiles over time. These changes in temperature profiles were then used to calculate the corresponding thermal diffusivity of the studied specimen. Thermal diffusivity for porcine fat was found to be lower by one order of magnitude than that obtained for agar (0.313×10(-7)m(2)/s vs. 4.83×10(-7)m(2)/s, respectively, p < 0.041). The fact that there is a substantial difference between agar and fat implies that non-invasive all-ultrasound thermal diffusivity mapping is feasible. The suggested method may particularly be suitable for breast scanning.

Magnetic nanoparticle clusters radiosensitise human nasopharyngeal and lung cancer cells after alternating magnetic field treatment

PURPOSE

Heat generated by magnetic nanoparticle clusters (MNCs) in an alternating magnetic field (AMF) can be used for hyperthermia cancer treatment. Here, we have synthesised polyacrylic acid-coated MNCs according to previous report, with the ability to increase particle stability in suspension. Radiosensitisation effects of the MNCs under an AMF were investigated in vitro and in vivo.

MATERIALS AND METHODS

MTT assay, flow cytometry, clone formation assay, Western blotting, and a γ-H2AX experiment were used to explore the biocompatibility and radiosensitisation effect of the MNCs and their putative radiosensitisation mechanism. An NCI-H460 mouse xenograft model was used to investigate the anti-tumour effect under an AMF in vivo.

RESULTS

The temperature of MNC fluids at different concentrations (200 μg/mL to 2 mg/mL) increased rapidly. The MNCs were endocytosed by the cells and were found to be biocompatible. Hsp70 and caspase-3 were found to be up-regulated upon MNCs under an AMF, radiation, and combination of both treatments. MNCs under an AMF efficiently radiosensitised both CNE-2 cells and NCI-H460 cells. Finally, the tumour inhibition rate after treatment with MNCs under an AMF and radiation was significantly higher than that after either treatment alone. The mechanism of radiosensitisation putatively involves inhibition of DNA repair and induction of apoptosis.

CONCLUSIONS

The MNC fluids under an AMF enhanced the radiosensitivity of tumour cells both in vitro and in vivo.

High intensity focused ultrasound: A noninvasive therapy for locally advanced pancreatic cancer

The noninvasive ablation of pancreatic cancer with high intensity focused ultrasound (HIFU) energy is received increasingly widespread interest. With rapidly temperature rise to cytotoxic levels within the focal volume of ultrasound beams, HIFU can selectively ablate a targeted lesion of the pancreas without any damage to surrounding or overlying tissues. Preliminary studies suggest that this approach is technical safe and feasible, and can be used alone or in combination with systemic chemotherapy for the treatment of patients with locally advanced pancreatic cancer. It can effectively alleviate cancer-related abdominal pain, and may confer an additional survival benefit with few significant complications. This review provides a brief overview of HIFU, describes current clinical applications, summarizes characteristics of continuous and pulsed HIFU, and discusses future applications and challenges in the treatment of pancreatic cancer.

Carbon nanotubes in hyperthermia therapy

Thermal tumor ablation therapies are being developed with a variety of nanomaterials, including single- and multiwalled carbon nanotubes. Carbon nanotubes (CNTs) have attracted interest due to their potential for simultaneous imaging and therapy. In this review, we highlight in vivo applications of carbon nanotube-mediated thermal therapy (CNMTT) and examine the rationale for use of this treatment in recurrent tumors or those resistant to conventional cancer therapies. Additionally, we discuss strategies to localize and enhance the cancer selectivity of this treatment and briefly examine issues relating the toxicity and long term fate of CNTs.

High intensity focused ultrasound ablation and antitumor immune response

The ideal cancer therapy not only induces the death of all localized tumor cells without damage to surrounding normal tissue, but also activates a systemic antitumor immunity. High intensity focused ultrasound (HIFU) has the potential to be such a treatment, as it can non-invasively ablate a targeted tumor below the skin surface, and may subsequently augment host antitumor immunity. This paper is to review increasing pre-clinical and clinical evidence linking antitumor immune response to HIFU ablation, and to discuss the potential mechanisms involved in HIFU-enhanced host antitumor immunity. The seminal studies performed so far indicate that although it is not possible to conclude definitively on the connection between HIFU treatment and antitumor immune response, it is nonetheless important to conduct extensive studies on the subject in order to elucidate the processes involved.

The resistance of breast cancer stem cells to conventional hyperthermia and their sensitivity to nanoparticle-mediated photothermal therapy

Breast tumors contain a small population of tumor initiating stem-like cells, termed breast cancer stem cells (BCSCs). These cells, which are refractory to chemotherapy and radiotherapy, are thought to persist following treatment and drive tumor recurrence. We examined whether BCSCs are similarly resistant to hyperthermic therapy, and whether nanoparticles could be used to overcome this resistance. Using a model of triple-negative breast cancer stem cells, we show that BCSCs are markedly resistant to traditional hyperthermia and become enriched in the surviving cell population following treatment. In contrast, BCSCs are sensitive to nanotube-mediated thermal treatment and lose their long-term proliferative capacity after nanotube-mediated thermal therapy. Moreover, use of this therapy in vivo promotes complete tumor regression and long-term survival of mice bearing cancer stem cell-driven breast tumors. Mechanistically, nanotube thermal therapy promotes rapid membrane permeabilization and necrosis of BCSCs. These data suggest that nanotube-mediated thermal treatment can simultaneously eliminate both the differentiated cells that constitute the bulk of a tumor and the BCSCs that drive tumor growth and recurrence.

Pathophysiological and vascular characteristics of tumours and their importance for hyperthermia: heterogeneity is the key issue

Tumour blood flow before and during clinically relevant mild hyperthermia exhibits pronounced heterogeneity. Flow changes upon heating are not predictable and are both spatially and temporally highly variable. Flow increases may result in improved heat dissipation to the extent that therapeutically relevant tissue temperatures may not be achieved. This holds especially true for tumours or tumour regions in which flow rates are substantially higher than in the surrounding normal tissues. Changes in tumour oxygenation tend to reflect alterations in blood flow upon hyperthermia. An initial improvement in the oxygenation status, followed by a return to baseline levels (or even a drop to below baseline at high thermal doses) has been reported for some tumours, whereas a predictable and universal occurrence of sustained increases in O(2) tensions upon mild hyperthermia is questionable and still needs to be verified in the clinical setting. Clarification of the pathogenetic mechanisms behind possible sustained increases is mandatory. High-dose hyperthermia leads to a decrease in the extracellular and intracellular pH and a deterioration of the energy status, both of which are known to be parameters capable of acting as direct sensitisers and thus pivotal factors in hyperthermia treatment. The role of the tumour microcirculatory function, hypoxia, acidosis and energy status is complex and is further complicated by a pronounced heterogeneity. These latter aspects require additional critical evaluation in clinically relevant tumour models in order for their impact on the response to heat to be clarified.

Mechanisms of Focal Heat Destruction of Liver Tumors

BACKGROUND

Focal heat destruction has emerged as an effective treatment strategy in selected patients with malignant liver tumors. Radiofrequency ablation, interstitial laser thermotherapy, and microwave treatment are currently the most widely applied thermal ablative techniques. A major limitation of these therapies is incomplete tumor destruction and overall high recurrences. An understanding of the mechanisms of tissue injury induced by focal hyperthermia is essential to ensure more complete tumor destruction. Here, the currently available scientific literature concerning the underlying mechanisms involved in the destruction of liver tumors by focal hyperthermia is reviewed.

METHODS

Medline was searched from 1960 to 2004 for literature regarding the use of focal hyperthermia for the treatment of liver tumors. All relevant literature was searched for further references.

RESULTS

Experimental evidence suggests that focal hyperthermic injury occurs in two distinct phases. The first phase results in direct heat injury that is determined by the total thermal energy applied, tumor biology, and the tumor microenvironment. Tumors are more susceptible to heat injury than normal cells as the result of specific biological features, reduced heat dissipating ability, and lower interstitial pH. The second phase of hyperthermic injury is indirect tissue damage that produces a progression of tissue injury after the cessation of the initial heat stimulus. This progressive injury may involve a balance of several factors, including apoptosis, microvascular damage, ischemia-reperfusion injury, Kupffer cell activation, altered cytokine expression, and alterations in the immune response. Blood flow modulation and administration of thermosensitizing agents are two methods currently used to increase the extent of direct thermal injury. The processes involved in the progression of thermal injury and therapies that may potentially modulate them remain poorly understood.

CONCLUSION

Focal hyperthermia for the treatment of liver tumors involves complex mechanisms. Evidence suggests that focal hyperthermia produces both direct and indirect tissue injury by differing underlying processes. Methods to enhance the effects of treatment to achieve complete tumor destruction should focus on manipulating these processes.

Chemoradiotherapy Combined With Intracavitary Hyperthermia for Anal Cancer

PURPOSE

The purpose of this study was to investigate in a randomized way the clinical benefit of addition of intracavitary hyperthermia (ICHT) to a conventional chemoradiotherapy schedule in patients with T2-T3N0M0 anal cancer.

METHODS AND MATERIALS

Patients were randomly assigned to undergo chemotherapy with 5-fluorouracil (5-FU) and mitomycin-C combined with radiotherapy with (arm A: 24 patients) or without ICHT (arm B: 25 patients). A microwave applicator operating at 433 MHz inserted into the anal-rectal cavity was used for ICHT. Patients in both arms received 1000 mg/m2 per day of 5-FU on days 1-4 and days 28-31 plus 15 mg/m mitomycin-C on day 1. Radiotherapy was administered with a dose of 41.4 Gy (1.8 Gy per fraction) plus a booster dose of 14 Gy (2 Gy per fraction).

RESULTS

One patient from group A developed severe mucositis, whereas no severe morbidity was noted in the rest of the patients in both groups. The incidence of lower-intestine acute reactions was higher in the ICHT arm. After a 5-year follow up in the hyperthermia arm, 23 of 24 patients (95.8%) preserved their anorectal function and avoided permanent colostomy, whereas in the second arm, 17 of 25 (68.0%) had sphincter preservation. Local recurrence-free survival time was significantly higher in the ICHT arm (P = 0.0107, log rank test), whereas no significant difference in overall survival was noted.

CONCLUSION

The addition of ICHT to the chemoradiotherapy schedule of anal cancer seems to offer a new effective and safe therapeutic modality. The preservation of anorectal function seems to be the significant clinical benefit of adjuvant ICHT.

Progressive microvascular injury in liver and colorectal liver metastases following laser induced focal hyperthermia therapy

BACKGROUND AND OBJECTIVES

Focal hyperthermia by laser or radiofrequency is currently the preferred method for local ablation of liver tumors. The underlying mechanism of action of focal hyperthermia, in particular the relationship between the microvascular and tissue effect is uncertain and was investigated in a murine model.

STUDY DESIGN/MATERIALS AND METHODS

Focal hyperthermia produced by a Neodymium-Yttrium-Aluminium-Garnet laser (wavelength 1,064 nm) was applied to the normal liver and colorectal cancer liver metastases in inbred male CBA strain mice at 2 W for 50 seconds (100 J). Tissue injury was assessed at 0, 24, 48, 72, 120, and 168 hours following therapy by measurements of necrosis in tissue sections stained for nicotinamide adenine dinucleotide (NADH) diaphorase activity. Characteristics of microvascular injury were assessed at the various time points by scanning electron microscopy (SEM) of vascular resin casts, Laser Doppler flowmetry, and confocal in vivo microscopy.

RESULTS

Focal hyperthermia produced progressive tissue and vascular injury. There was an initial reduction in blood flow and increased vascular permeability in the microcirculation of both tumor and liver tissue immediately following heat application as assessed by laser Doppler flowmetry and confocal in vivo microscopy, respectively. SEM of vascular casts showed heterogeneous regions of microvascular injury immediately following heat application. The extent of initial vascular disruption or occlusion on SEM of vascular resin casts (mean+/-SE) was significantly less than the tissue necrosis in liver (1.9+/-0.1 mm vs. 3.0 mm+/-0.2 mm P<0.001), but was equivalent to the tissue injury in tumor tissue (3.5 mm+/-0.2 mm vs. 3.6 mm+/-0.1 mm P = 0.907). This was followed by a progressive increase in both microvascular and tissue injury in liver and tumor that peaked by 72 hours following treatment. The peak microvascular injury and tissue damage in liver (6.6 mm+/-0.2 and 6.3 mm+/-0.2 mm, respectively) was significantly greater than the extent of microvascular and tissue damage in tumors (4.8 mm+/-0.2 mm and 4.5 mm+/-0.2 mm, respectively) (P<0.001). The progression of microvascular injury in liver and tumor at times preceded the tissue injury.

CONCLUSION

Focal hyperthermia produces both progressive microvascular and tissue damage in liver and colorectal liver metastases. An increase in tissue injury following focal hyperthermia may be a direct result of progressive microvascular damage. Tumor vessels appear more susceptible to direct focal hyperthermia destruction than liver sinusoids. The liver sinusoids are however more susceptible to progressive damage or occlusion following the initial laser thermal stimulus.

Optimization of a beam shaping bolus for superficial microwave hyperthermia waveguide applicators using a finite element method

Temperature inhomogeneity in hyperthermia treatments often limits the total thermal dose that can be delivered to the tumour region. To reduce such inhomogeneities, a prototype dynamically modifiable square array of saline-filled patches which attenuate microwave energy was developed for superficial treatments that use external microwave applicators. The array was situated inside the coupling water bolus that is often used with external applicators. The prototype has been previously tested clinically with promising results. A more complete theoretical analysis of the performance of this new bolus design and improvements to its design by modelling are presented here. The analysis was performed by performing five iterative simulations of the SAR pattern produced inside a tissue structure by a waveguide applicator with a water bolus containing the dynamic patch array attached. Between iterations the patch array configuration was modified in an attempt to improve the ability of the bolus to confine heating to an 'L'-shaped tumour region. These simulations were performed using the finite element method. The steady-state temperature profile was then computed using a finite element method based simulation of heat transfer that assumed a given applicator power level and water bolus temperature. Several iterations of these heat transfer simulations were performed with varying applicator power level and water bolus temperature to improve the confinement of heating to the target region. The analysis showed that the dynamic patch array should be capable of conforming heating to an 'L'-shaped target tumour region while limiting the heating to the surrounding normal tissue to an acceptable level.

Tissue thermal conductivity by magnetic resonance thermometry and focused ultrasound heating

PURPOSE

To investigate the combined use of magnetic resonance (MR) temperature imaging and focused ultrasound (FUS) for the noninvasive determination of tissue thermal properties.

MATERIALS AND METHODS

Brief, spatial impulses of temperature elevation were created in tissue using a spherical, air-backed transducer operating at 1.68 MHz and measured using MR temperature imaging in a 1.5-Tesla clinical scanner. A novel technique based on thermal washout is applied in an analysis of the acquired MR temperature images to estimate tissue thermal conductivity and perfusion.

RESULTS

Numerical simulations and experiments in vitro and in vivo demonstrate that thermal conductivity can be measured to within 10% of the true value with MR thermometry at 1.5 Tesla. With the temperature precision available at 1.5 Tesla, however, robust perfusion estimation is feasible only in highly perfused organs or tumors.

CONCLUSION

This study has developed a method for determining tissue thermal properties specific to the patient and organ at the site of interest, and allows repeated application. This capability is relevant in thermal therapy planning of tumor ablation using MR-guided FUS systems.

Silicon and iron levels in tissues of animals treated with a "ferrimagnetic ceramic" with oncotherapeutic potential (anti-tumor) value

The stability in a biological environment of an injectable cement with oncotherapeutic potential--consisting of a glass powder of SiO2 (35.6%), CaO (42.4%), P2O5 (17%), Na2O (5%) and 30% of its weight of Fe3O4 dissolved in (NH4)2HPO4 plus NH4H2PO4--was evaluated referring to the release of silicon and iron. The experimental model was the rat, and organs (liver, kidney, spleen, lung, heart, and brain) of the implanted and control animals were collected for quantification of these elements by electrothermal atomization atomic absorption spectrometry methods. In most of the analysed organs no significant difference in the contents of silicon and iron between the implanted and the control animals was found.

[Peritoneal carcinomatosis treated by cytoreductive surgery and intraperitoneal chemohyperthermia]

STUDY AIM

The aim of this prospective non-randomized trial was to report a series of intraperitoneal carcinomatosis due to miscellaneous causes, treated by intraperitoneal hyperthermic perfusion (IPHP) and cytoreductive surgery.

PATIENTS AND METHOD

From January 1995 to May 1999, 35 patients were treated by IPHP and 26 of them underwent maximal cytoreductive surgery. IPHP was performed for 60 minutes at an intraperitoneal temperature of 42 degrees C with Mitomycin C (10 mg/L) or cisplatinum (12 mg/L) at a flow rate of 0.9 L/min.

RESULTS

There was one (2.8%) postoperative death due to respiratory complications on day 16. Three patients (8.5%) were admitted to the intensive care unit. A high morbidity rate (54%) was observed with intra-abdominal complications in 28.5% of patients, requiring reoperation in three patients. In patients with stages 1 and 2 peritoneal carcinomatosis (granulations less than 5 mm), the 12- and 24-month survival rates were 63.1% and 31.5%, respectively. In patients with advanced stage 3 (diffuse malignant nodules less than 2 cm) and stage 4 carcinomatosis (malignant nodules larger than 2 cm), the 12- and 24-month survival rates were 31.2% and 12%, respectively. Six patients survived for more than 30 months.

CONCLUSION

IPHP appears to be an effective treatment for peritoneal carcinomatosis. IPHP combined with cytoreductive surgery is aggressive with a high morbidity rate. Rigorous patient selection is necessary. IPHP is still under evaluation. Prospective randomized trials with identical IPHP protocols are required.

Effects of a combined thermochemotherapy on markers of apoptosis, differentiation and adhesion in the human mammary carcinoma MX-1. A light microscopic and immunohistochemical study

The susceptibility to apoptotic stimuli, the degree of differentiation and the adhesive properties are important determinants of a tumor's biological behavior and of the possibility of it's being influenced by treatment. In this study we examined the effects of a combined thermochemotherapy, consisting of the administration of the alkylating agents ifosfamide or mafosfamide combined with hyperthermia at 41 degrees C for one hour, applied to the human mammary carcinoma MX-1. We concentrated our observations on the apoptosis-associated proteins bax and bcl-2, on cytokeratin and vimentin as markers of differentiation, on desmosomes and on the antiadhesive epithelial membrane antigen episialin. These proteins were visualized immunohistochemically in cultured cells in vitro as well as in xenotransplants growing in nude mice in vivo. We found that the susceptibility of the surviving cells to apoptotic stimuli, measured by the bax/bcl-2 ratio, was much higher after a combined thermochemotherapy than after chemotherapy or thermotherapy alone. Many of these cells could probably be forced into apoptosis by later applying another kind of anticancer therapy. With regard to the expression of episialin after thermochemotherapy, fewer cells possessed an antiadhesive and, therefore, potentially invasive capacity. The number of desmosomes seemed not to be affected. As to their higher expression of cytokeratin and their unchanged expression of vimentin, the surviving cells appear to be more differentiated. Since these results could be observed in vivo as well as in vitro, it seems likely that, apart from its influence on the perfusion of the tumor, the amplification of the cytostatic efficacy of the chemotherapy by hyperthermia must be mediated by a direct mechanism.

Hyperthermia and liposomes

Hyperthermia and liposomal drug delivery are treatment modalities that have been used to treat cancer over the last two decades. More recently, the two therapies have been used together in an attempt to exploit their mutual interactions against cancer. The goal of this review is to explore the literature related to combined hyperthermia and liposomal drug delivery for cancer therapy. The motivation behind combining hyperthermia and liposomal drug delivery is discussed from a physical chemical and physiological standpoint. Two types of therapeutic ratios were calculated for in vivo studies from across the literature. These ratios compared the results obtained from hyperthermia and liposomes to hyperthermia and free drug as well as to liposomes without hyperthermia. These two therapeutic ratios were applied to both tumour drug uptake and tumour growth delay studies. In all studies reviewed, hyperthermia in combination with liposomal drug showed an enhanced therapeutic effect compared to either treatment modality alone or hyperthermia and free drug. Future work needs to be focused on optimizing thermosensitive liposomes and understanding the effect of thermal dose on liposomal drug delivery. Though not currently used in the clinic, this combination therapy seems to hold great promise towards improving current cancer therapeutic regimens.

Perfusion and thermal field during hyperthermia. Experimental measurements and modelling in recurrent breast cancer

Recurrences of malignant tumours in the chest wall are proposed as a valuable model of tissue mainly perfused by small size vessels (the so-called 'phase III' vessels). Invasive thermal measurements have been performed on two patients affected by cutaneous metastasis of malignant tumours during hyperthermic sessions. Thermal probes were inserted into catheters implanted into the tissue at different depths. In one of the catheters a probe connected with laser-Doppler equipment was inserted to assess blood perfusion in the tumour periphery. The perfusion was monitored throughout the sessions, and a noticeable temporal variability was observed. The effect of the perfusion on the thermal map in the tissue was evaluated locally and the 'effective conductivity' of the perfused tissue was estimated by means of the numerical integration of the 'bio-heat' equation. The tumour temperature, at the site where the perfusion probe is located, can be predicted by the numerical model provided two free parameters, alpha and beta, are evaluated with a fitting procedure. Alpha is related to the effective conductivity and beta to the SAR term of the bio-heat equation. The model aimed at estimating the 'effective conductivity' K(eff) of the perfused tissue, and average values of K(eff) of 0.27 +/- 0.03 W m(-1) degrees C(-1) in Patient 1 and of 0.665 +/- 0.005 W m(-1) degrees C(-1) in Patient 2 were obtained throughout the treatment. However, when the average temperature in a larger tumour volume is to be predicted but only a single, 'local' measurement of the perfusion is available and is assumed to be representative for the whole region, the model results are far less satisfactory. This is probably due to the fact that changes of blood perfusion throughout hyperthermic sessions occur to different extents within the tumour volume, and the differences in perfusion cannot be ignored. The above result suggests that, in addition to the 'temperature map', also a 'perfusion map' within the heated volume should be monitored routinely throughout hyperthermic sessions.

Measurement of intratumor pH by pH indicator used in 19F-magnetic resonance spectroscopy. Measurement of extracellular pH decrease caused by hyperthermia combined with hydralazine

RATIONALE AND OBJECTIVES

Without affect of metabolic changes, the authors measured intratumor pH by using 19F-magnetic resonance spectroscopy (MRS) with a fluorine compound (ZK-150471) on the basis of a calibration curve by pH electrode.

METHODS

Using the 4.7-tesla magnetic resonance apparatus, a fluorine compound that had acid-base equilibrial change and was impermeable within cell membranes was used. The fluorine compound was injected intravenously. The signal was obtained from mouse mammary cancer by creating an experimental tumor on the leg of mice. And the tumors, which were heated with and without hydralazine. The pH evaluated from chemical shift of the fluorine compound. The pH data was obtained from an electrode for reference.

RESULTS

The pH of nontreated tumors (n = 25) were 6.94 + 0.091. The pH decreased to 6.772 + 0.169 at 20 minutes even after 20 minutes of heating, and decreased to < 6.71 at 40 minutes after every heating time. The pH decreased to 6.456 at 20 minutes after 15 minutes of heating combined with hydralazine, and to 6.416 at 40 minutes after same treatment.

CONCLUSIONS

It is possible to measure the extracellular pH by 19F-MRS with the fluorine compound noninvasively in vivo, even after heating.

Hyperthermia in the multimodal therapy of advanced rectal carcinomas

The synergistic effects of hyperthermia (raising temperatures to 40 degrees C and above) when combined with radiotherapy and cytotoxic drugs and a modulation of immunological phenomena have been demonstrated in the laboratory. Pre-clinical data relating to hyperthermia are summed up, along with their implications for clinical application. Controlled studies of local and regional hyperthermia have been performed during recent years, and these show us that the adjunction of hyperthermia provides at least an improvement of local control compared with radiotherapy alone. Current clinical results are summarized. Therapy systems based on radiowave irradiation have been commercially available for regional hyperthermia of the pelvis since the mid 1980s. This technology allows us to perform sufficiently tolerable and effective regional hyperthermia on rectal carcinomas. Used as part of curative preoperative and postoperative multimodal therapeutic strategies, hyperthermia can lead to improvement in local control (resectability, down-staging, progression-free time, recurrence rate), at least for certain risk groups. The preoperative radio-chemo-thermotherapy of advanced primary and recurring rectal carcinoma, uT3/4, was tested in a phase-I/II study of 20 patients. Therapy procedure, acute toxicity, thermal parameters, and response are described and discussed for this patient group. The regimen proved to be sufficiently tolerable, and complications did not occur. Tumor resection was performed on 14 of the 20 patients; 13 of the procedures were R0-resections and one was an R2 resection. In 64% of the resected rectal carcinomas, histopathological down-staging of the pretherapeutic endosonographical stadium was achieved; in three of the patients, despite continued non-resectability, local control has now been maintained for more than 12 months. In two patients with nonresectable rectal carcinomas, local progress was seen during the neoadjuvant combination therapy.

Response of 145 spontaneous canine head and neck tumours to radiation versus radiation plus microwave hyperthermia: results of a randomized phase III clinical study

The results of a phase III, clinical trial of local microwave hyperthermia (target = 2 x 44 degrees C for 30 min) and megavoltage radiation (4 x 9 Gy fractions) in the treatment of 145 naturally occurring canine head and neck cancers are reported. Patients were re-examined at regular intervals following treatment until death. The median follow up time was 90 weeks. Tumour response, patient survival and normal tissue toxicity were analysed by treatment allocation. There was no significant difference in best tumour response nor patient survival between the two treatment groups. There was no difference in acute normal tissue toxicity but there was a suggestion that patients receiving RT and HT may suffer a higher incidence of late skin reactions. Histological type and tumour volume were of prognostic significance with smaller tumours and carcinomas showing higher response rates. There were also positive associations between minimum tumour dose and best tumour response and percentage of tumour heated and best tumour response. The results of this study must be interpreted in the knowledge of limitations on the dose and fractionation schedule for radiation therapy, the small number of hyperthermia treatments applied and the variation in tumour type and size that is inevitable in a clinical study. It is concluded that the quality of hyperthermia in terms of intra-tumour temperatures and the uniformity of heating is of paramount importance in governing response to adjuvant hyperthermia.

Step-down heating of human melanoma xenografts: effects of the tumour microenvironment

Thermosensitisation by step-down heating (SDH) has previously been demonstrated in experimental rodent tumours. The purpose of the study reported here was to investigate whether the SDH effect in tumours in part may be attributed to heat-induced alterations in the capillary network and/or the microenvironment. Two human melanoma xenograft lines differing substantially in vascular parameters were selected for the study. A thermostatically regulated water bath was used for heat treatment. The conditioning treatment (44.5 degrees C or 45.5 degrees C for 15 min) was given in vivo, whereas the test treatment (42.0 degrees C for 45, 90, 135 or 180 min) was given either in vitro or in vivo. Treatment response was measured in vitro using a cell clonogenicity assay. Fraction of occluded vessels following heat treatment was assessed by examination of histological sections from tumours whose vascular network was filled with a contrast agent. Tumour bioenergetic status and tumour pH were measured by 31P magnetic resonance spectroscopy. The conditioning heat treatments caused significant vessel occlusion, decreased tumour bioenergetic status and decreased tumour pH in both tumour lines. The SDH effect measured when the test treatment was given in vivo was significantly increased relative to that measured when the test treatment was given in vitro. The magnitude of the increase showed a close relationship to fraction of occluded vessels, tumour bioenergetic status and tumour pH measured 90 min after treatment with 44.5 degrees C or 45.5 degrees C for 15 min. The increased SDH effect in vivo was probably attributable to tumour cells that were heat sensitive owing to the induction of low nutritional status and pH during the conditioning treatment. Consequently, the SDH effect in some tumours may in part be due to heat-induced alterations in the microenvironment. This suggests that SDH may be exploited clinically to achieve increased cell inactivation in tumours relative to the surrounding normal tissues.

Effect of hyperthermia on cisplatin and carboplatin disposition in the isolated, perfused tumour and skin flap

The effect of hyperthermia on the disposition of platinum (Pt) from cisplatin (CDDP) and carboplatin (CBDCA) in the isolated, perfused tumour and skin flap (IPTSF) was evaluated. Flaps (n = 4/treatment) were perfused with 3.0 micrograms CDDP or 15 micrograms CBDCA/ml perfusion medium at a rate of 1 ml/min for 3 h. Two-hour (CDDP experiments) or 3 h (CBDCA experiments) washout phases were then performed. The disposition kinetics of free Pt were characterized using a four-compartment, physiologically relevant, pharmacokinetic model. Hyperthermia (HT) may have enhanced the mobility of Pt but it did not increase total Pt mass in the tissue compartments in CDDP experiments. Conversely, HT significantly increased Pt mass in the fixed, non-tumour tissue compartment (p < 0.05) in CBDCA experiments. While a similar trend was noted in the fixed, tumour tissue compartment of CBDCA-treated flaps, the difference was not significant (p = 0.17). Total tissue Pt mass was significantly greater in CDDP compared with CBDCA experiments (p < 0.05). In conclusion, HT alters the disposition of Pt from CDDP and CBDCA under conditions of constant rate infusion. Further characterization of factors influencing drug disposition to non-tumour and tumour tissues can be systematically accomplished using the IPTSF.

Heating as a mechanism for ultrasonically-induced petechial hemorrhages in mouse intestine

Anesthetized hairless mice were exposed to 1.035 MHz unfocused ultrasound in a temperature-controlled water bath. Visible petechial hemorrhages and hyperemia were produced in the intestines. Histologically, the petechiae appeared to be localized mostly to the lamina propria of the mucosa. For 2 min exposure, the number of petechiae and length of hyperemic tissue both increased with increasing spatial peak pressure amplitude above a threshold of about 0.4-0.57 MPa. The magnitude of these effects increased, and the threshold decreased, with increasing exposure duration from 1 min to 4 min. The effects also increased for increasing bath temperature from 32 degrees C to 42 degrees C. The effects decreased markedly for 1 ms burst-mode exposure with 2 ms and 4 ms repetition periods with constant pressure amplitude, but were essentially constant for constant temporal-average intensity. Both effects were also produced by heating from radio-frequency diathermy at 10.35 MHz. The effects were associated with abdominal temperatures above about 42-43 degrees C, which were estimated with a thermocouple at the end of the exposure. The hyperemia is a clearly thermal effect, while the petechiae have been previously associated with the cavitation mechanism. However, the ultrasonically-induced petechiae observed in this study do not represent an unequivocal marker for cavitation, but rather appear to be attributable to heating. These findings help to reduce the expectation of ultrasonic cavitation during medical therapy treatments.

Thermal dose and secondary tumour cell death

Both primary and secondary tumour cell death may occur in clinical hyperthermia. The equation usually used for calculation of thermal dose takes only the primary cell death into consideration. We propose that the thermal dose equation should be reassessed; contributions from secondary cell death should also be included. The secondary cell death is governed mainly by the temperature distribution during treatment, the arteriolar density distribution in the tumour and the heat sensitivity of the arterioles. Increased thermal dose and hence increased tumour treatment response may result if hyperthermic treatments are designed to maximize the secondary cell death. Massive secondary cell death may be achieved by inducing hot spots in tumour areas with high arteriolar density, identified in pretreatment tumour angiograms.

Review: transurethral microwave thermotherapy in benign prostatic hyperplasia

The transurethral microwave thermotherapy (TUMT) method combines the principles of microwave radiative heating and conductive cooling to destroy tissue within the prostate while preserving the other structures of the lower urinary tract. The method is effective in benign prostatic hyperplasia (BPH), as demonstrated by laboratory and clinical studies. The ease of the 1-hour office treatment, the dramatic symptomatic improvement and reasonable uroflow rates that result, the preservation of sexual function, the apparent safety, and the durability of the result may mean that TUMT will introduce changes in the management of BPH as dramatic as those brought about in lithiasis management by ESWL.

Equilibrium temperature distributions in uniform phantoms for superficial microwave applicators: implications for temperature-based standards of applicator adequacy

Equilibrium temperature distributions are computed using measured SAR distributions for five different superficial microwave (915 MHz) applicators. We assume a model with uniform conduction and blood flow. A Green's function approach is used to calculate equilibrium solutions which identically obey boundary conditions at the surface of the phantom and at infinite depth. The equilibrium solutions are categorized by surface temperature (TS), maximum allowed temperature (TM), and by a parameter (referred to as the diffusion length, lambda) which characterizes the contributions of thermal conduction relative to blood flow. The computed equilibrium temperature distribution at depths of 2 and 3 cm is strongly dependent on lambda and on TM. It is not strongly dependent on surface temperature for TS below 35 degrees C. In previous work we compared the SAR distribution with local control of 53 superficial tumours with over 1 year of follow-up. As an alternative to an SAR-based description of applicator adequacy we consider a temperature-based standard. Tumours are categorized by the minimum value of lambda that would allow full coverage of the tumour volume by the 42 degrees C contour, assuming a TM of 47.5 degrees C and a TS of 35 degrees C. Eighteen of 27 lesions (67%) were locally controlled for lambda less than 1 cm. The local control in 26 lesions with lambda greater than or equal to 1 cm was 31% (p = 0.016). The lesions with the best results were those with both good coverage in theory (lambda less than 1 cm) and with all monitored catheter tracks achieving at least one session with 30 min at or above 43 degrees C. We found that the temperature-based standard of applicator adequacy was not independent of an SAR-based standard, and in this cohort of patients either a minimum SAR criterion or a maximum diffusion length criterion would serve equally well as a screen for inappropriate applicators.

Interventional radiology of the lower urinary tract and its relationship to surgical treatment

Interventional radiological techniques of the lower genitourinary (GU) tract are large and varied and continue to expand because of technological advances and also because budgetary restraints are being placed on our medical society. This has stimulated continuous search for alternative ways of treating disease in a more cost-effective fashion. As a result, there has been an overall decrease in morbidity and mortality, as well as postprocedural incapacity. We review the most important and newest modalities and provide some background of the processes affecting the lower GU tract.

The relevance of tumour and surrounding normal tissue vascular density in clinical hyperthermia of locally advanced breast carcinoma

It follows from the present work that the vascularization of the normal tissue present in the treatment volume limits the temperatures achieved during heat treatment of invasive ductal breast carcinoma. The temperatures can often be increased by giving fractionated heat treatment because heat treatment may reduce the cooling capacity of the normal tissue vasculature. Significant damage to supplying vessels occurs at the heat doses necessary to cause necrosis in the tumour and surrounding normal tissue, indicating that secondary cell death is an important mechanism for cell inactivation following hyperthermic treatment of breast carcinoma.