Interstitial microwave thermal therapy and its application to the treatment of recurrent prostate cancer

Selecting High-Performance Gold Nanorods for Photothermal Conversion

In this work, we establish a new paradigm on identifying optimal arbitrarily shaped metallic nanostructures for photothermal applications. Crucial thermo-optical parameters that rule plasmonic heating are appraised, exploring a nanoparticle size-dependence approach. Our results indicate two distinct figures of merit for the optimization of metallic nanoheaters, under both non-cumulative femtosecond and continuum laser excitation. As a case study, gold nanorods are evaluated for infrared photothermal conversion in water, and the influence of the particle length and diameter are depicted. For non-cumulative femtosecond pulses, efficient photothermal conversion is observed for gold nanorods of small volumes. For continuous wave (CW) excitation at 800 nm and 1064 nm, the optimal gold nanorod dimensions (in water) are, respectively, 90 × 25nm and 150 × 30 nm. Figure of Merit (FoM) variations up to 700% were found considering structures with the same peak wavelength. The effect of collective heating is also appraised. The designing of high-performance plasmonic nanoparticles, based on quantifying FoM, allows a rational use of nanoheaters for localized photothermal applications.

Microwave for focal therapy of prostate cancer: Non-clinical study and exploratory clinical trial

OBJECTIVE

The objective of this non-clinical study and clinical trial (phase II) was to examine the safety and efficacy of microwave tissue coagulation (MTC) for prostate cancer and assess its use in lesion-targeted focal therapy.

METHODS

In the non-clinical study using Microtaze®-AFM-712 (Alfresa-pharma Corporation) with an MTC-needle, MTC was performed by a transperineal approach to canine prostatic-targeted tissue under real-time ultrasound guidance. Using various MTC-output and irradiation-time combinations, the targeted and surrounding tissues (rectum, bladder, and fat) were examined to confirm the extent of coagulative necrosis or potential cell death, and to compare intra-operative ultrasound and pathology findings. The exploratory clinical trial was conducted to examine the safety and efficacy of MTC. Five selected patients underwent transperineal MTC to clinically single magnetic resonance imaging (MRI)-visible lesions with Gleason score 3+4 or 4+4. Prostate-specific antigen (PSA), MRI, and Expanded Prostate Cancer Index Composite questionnaire findings were compared before and 6 months after surgery.

RESULTS

The region of coagulative necrosis was predictable by monitoring of ultrasonically visible vaporization; thus, by placing the MTC-needle at a certain distance, we were able to perform a safe procedure without adverse events affecting the surrounding organs. Based on the non-clinical study, which used various combinations of both output and irradiation time, MTC with 30-W output for 60-sec irradiation was selected for the prostate. Based on the predictable necrosis, the therapeutic plan (where to place the MTC-needle to achieve complete ablation of the target and how many sessions) was strictly determined per patient. There were no serious adverse events in all patients and only temporary urinary symptoms related to MTC-therapy were observed. Furthermore, satisfaction of having undergone treatment was very high. All pre-operative MRI-visible lesions disappeared, and PSA decreased 55% 6 months after surgery.

CONCLUSION

MTC may be an option for lesion-targeted focal therapy for prostate cancer.

Methods of monitoring thermal ablation of soft tissue tumors - A comprehensive review

Thermal ablation is a form of hyperthermia in which oncologic control can be achieved by briefly inducing elevated temperatures, typically in the range 50-80°C, within a target tissue. Ablation modalities include high intensity focused ultrasound, radiofrequency ablation, microwave ablation, and laser interstitial thermal therapy which are all capable of generating confined zones of tissue destruction, resulting in fewer complications than conventional cancer therapies. Oncologic control is contingent upon achieving predefined coagulation zones; therefore, intraoperative assessment of treatment progress is highly desirable. Consequently, there is a growing interest in the development of ablation monitoring modalities. The first section of this review presents the mechanism of action and common applications of the primary ablation modalities. The following section outlines the state-of-the-art in thermal dosimetry which includes interstitial thermal probes and radiologic imaging. Both the physical mechanism of measurement and clinical or pre-clinical performance are discussed for each ablation modality. Thermal dosimetry must be coupled with a thermal damage model as outlined in Section 4. These models estimate cell death based on temperature-time history and are inherently tissue specific. In the absence of a reliable thermal model, the utility of thermal monitoring is greatly reduced. The final section of this review paper covers technologies that have been developed to directly assess tissue conditions. These approaches include visualization of non-perfused tissue with contrast-enhanced imaging, assessment of tissue mechanical properties using ultrasound and magnetic resonance elastography, and finally interrogation of tissue optical properties with interstitial probes. In summary, monitoring thermal ablation is critical for consistent clinical success and many promising technologies are under development but an optimal solution has yet to achieve widespread adoption.

Durability study of a gellan gum-based tissue-mimicking phantom for ultrasonic thermal therapy

Stability and duration of ultrasonic phantoms are still subjects of research. This work presents a tissue-mimicking material (TMM) to evaluate high-intensity therapeutic ultrasound (HITU) devices, composed of gellan gum (matrix), microparticles (scatterers), and chemicals. The ultrasonic velocity and attenuation coefficient were characterized as a function of temperature (range 20 °C-85 °C). The nonlinear parameter B/A was determined by the finite amplitude insertion substitution (FAIS) method, and the shear modulus was determined by a transient elastography technique. The thermal conductivity and specific heat were determined by the line source method. The attenuation was stable for 60 days, and in an almost linear frequency dependence (0.51f^0.96dB cm^-1), at 20 °C (1-10 MHz). All other evaluated physical parameters are also close to typical soft tissue values. Longitudinal ultrasonic velocities were between 1.49 and 1.75 mm μs^-1, the B/A parameter was 7.8 at 30 °C, and Young's modulus was 23.4 kPa. The thermal conductivity and specific heat values were 0.7 W(m K)^-1 and 4.7 kJ(kg K)^-1, respectively. Consistent temperature increases and thermal doses occurred under identical HITU exposures. Low cost, longevity, thermal stability, and thermal repeatability make TMM an excellent material for ultrasonic thermal applications. The TMM developed has the potential to assess the efficacy of hyperthermia devices and could be used to adjust the ultrasonic emission of HITU devices.

Apoptosis of Lewis Lung Carcinoma Cells Induced by Microwave via p53 and Proapoptotic Proteins In vivo

Background:

Microwave therapy is a minimal invasive procedure and has been employed in clinical practice for the treatment of various types of cancers. However, its therapeutic application in non-small-cell lung cancer and the underlying mechanism remains to be investigated. This study aimed to investigate its effect on Lewis lung carcinoma (LLC) tumor in vivo.

Methods:

Fifty LLC tumor-bearing C57BL/6 mice were adopted to assess the effect of microwave radiation on the growth and apoptosis of LLC tumor in vivo. These mice were randomly assigned to 10 groups with 5 mice in each group. Five groups were treated by single pulse microwave at different doses for different time, and the other five groups were radiated by multiple-pulse treatment of a single dose. Apoptosis of cancer cells was determined by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. Western blotting was applied to detect the expression of proteins.

Results:

Single pulse of microwave radiation for 5 min had little effect on the mice. Only 15-min microwave radiation at 30 mW/cm² significantly increased the mice body temperature (2.20 ± 0.82)°C as compared with the other groups (0.78 ± 0.29 °C, 1.24 ± 0.52 °C, 0.78 ± 0.42 °C, respectively), but it did not affect the apoptosis of LLC tumor cells significantly. Continous microwave radiation exposure, single dose microwave radiation once per day for up to seven days, inhibited cell division and induced apoptosis of LLC tumor cells in a dose- and duration-dependent manner. It upregulated the protein levels of p53, Caspase 3, Bax and downregulated Bcl-2 protein.

Conclusions:

Multiple exposures of LLC-bearing mice to microwave radiation effectively induced tumor cell apoptosis at least partly by upregulating proapoptotic proteins and downregulating antiapoptotic proteins. Continuous radiation at low microwave intensity for a short time per day is promising in treating non-small-cell lung cancer.

A novel property of gold nanoparticles: Free radical generation under microwave irradiation

PURPOSE

Gold nanoparticles (GNPs) are known to be effective mediators in microwave hyperthermia. Interaction with an electromagnetic field, large surface to volume ratio, and size quantization of nanoparticles (NPs) can lead to increased cell killing beyond pure heating effects. The purpose of this study is to explore the possibility of free radical generation by GNPs in aqueous media when they are exposed to a microwave field.

METHODS

A number of samples with 500 mM 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in 20 ppm GNP colloidal suspensions were scanned with an electron paramagnetic resonance (EPR)/electron spin resonance spectrometer to generate and detect free radicals. A fixed (9.68 GHz) frequency microwave from the spectrometer has served for both generation and detection of radicals. EPR spectra obtained as first derivatives of intensity with the spectrometer were double integrated to get the free radical signal intensities. Power dependence of radical intensity was studied by applying various levels of microwave power (12.5, 49.7, and 125 mW) while keeping all other scan parameters the same. Free radical signal intensities from initial and final scans, acquired at the same power levels, were compared.

RESULTS

Hydroxyl radical (OH⋅) signal was found to be generated due to the exposure of GNP-DMPO colloidal samples to a microwave field. Intensity of OH⋅ signal thus generated at 12.5 mW microwave power for 2.8 min was close to the intensity of OH⋅ signal obtained from a water-DMPO sample exposed to 1.5 Gy ionizing radiation dose. For repeated scans, higher OH⋅ intensities were observed in the final scan for higher power levels applied between the initial and the final scans. Final intensities were higher also for a shorter time interval between the initial and the final scans.

CONCLUSIONS

Our results observed for the first time demonstrate that GNPs generate OH⋅ radicals in aqueous media when they are exposed to a microwave field. If OH⋅ radicals can be generated close to deoxyribonucleic acid of cells by proper localization of NPs, NP-aided microwave hyperthermia can yield cell killing via both elevated temperature and free radical generation.

Biocompatible Hollow Polydopamine Nanoparticles Loaded Ionic Liquid Enhanced Tumor Microwave Thermal Ablation in Vivo

Tumor microwave thermal therapy (MWTT) has attracted more attention because of the minimal damage to body function, convenient manipulation and low complications. Herein, a novel polydopamine (PDA) nanoparticle loading ionic liquids (ILs/PDA) as microwave susceptible agent is introduced for enhancing the selectivity and targeting of MWTT. ILs/PDA nanocomposites have an excellent microwave heating efficiency under an ultralow microwave power irradiation. Encouraging antitumor effect was observed when tumor bearing mice received ILs/PDA nanoparticles by intravenous injection and only single microwave irradiation. PDA nanoparticles with gold nanoparticles in core were constructed for tumor targeting study by ICP-MS and about 15% PDA nanoparticles were founded in tumor. Furthermore, the cytotoxicity and acute toxicity study in vivo of PDA showed the excellent biocompatibility of ILs/PDA nanocomposites. In addition, the degradation of ILs/PDA nanocomposites in simulated body fluid illustrated the low potential hazard when they entered the blood. The emergence of PDA as a novel and feasible platform for cancer thermal therapy will promote the rapid development of microwave therapy in clinics.

Improved hyperthermia treatment control using SAR/temperature simulation and PRFS magnetic resonance thermal imaging

PURPOSE

This article explores the feasibility of using coupled electromagnetic and thermodynamic simulations to improve planning and control of hyperthermia treatments for cancer. The study investigates the usefulness of preplanning to improve heat localisation in tumour targets in treatments monitored with PRFS-based magnetic resonance thermal imaging (MRTI).

METHODS

Heating capabilities of a cylindrical radiofrequency (RF) mini-annular phased array (MAPA) applicator were investigated with electromagnetic and thermal simulations of SAR in homogeneous phantom models and two human leg sarcomas. High frequency structure simulator (HFSS) (Ansoft) was used for electromagnetic simulations and SAR patterns were coupled into EPhysics (Ansoft) for thermal modelling with temperature-dependent variable perfusion. Simulations were accelerated by integrating tumour-specific anatomy into a pre-gridded whole body tissue model. To validate this treatment planning approach, simulations were compared with MR thermal images in both homogenous phantoms and heterogeneous tumours.

RESULTS

SAR simulations demonstrated excellent agreement with temperature rise distributions obtained with MR thermal imaging in homogeneous phantoms and clinical treatments of large soft-tissue sarcomas. The results demonstrate feasibility of preplanning appropriate relative phases of antennas for localising heat in tumour.

CONCLUSIONS

Advances in the accuracy of computer simulation and non-invasive thermometry via MR thermal imaging have provided powerful new tools for optimisation of clinical hyperthermia treatments. Simulations agree well with MR thermal images in both homogeneous tissue models and patients with lower leg tumours. This work demonstrates that better quality hyperthermia treatments should be possible when simplified hybrid model simulations are performed routinely as part of the clinical pretreatment plan.

Interstitial microwave transition from hyperthermia to ablation: historical perspectives and current trends in thermal therapy

This work reviews the transition from hyperthermia to ablation for cancer treatment with interstitial microwave (MW) antennas. Early work utilising MW energy for thermal treatment of cancer tissue began in the late 1970s using single antennas applied interstitially or the use of multiple interstitial antennas driven with the same phase and equal power at 915 or 2450 MHz. The original antenna designs utilised monopole or dipole configurations. Early work in thermal therapy in the hyperthermia field eventually led to utilisation of these antennas and methods for MW ablation of tumours. Efforts to boost the radiated MW power levels while decreasing antenna shaft temperatures led to incorporation of internally cooled antennas for ablation. To address larger tumours, MW treatment utilised arrays that were simultaneously activated by either non-synchronous or synchronous phase operation, benefiting both hyperthermia and ablation strategies. Numerical modelling was used to provide treatment planning guidance for hyperthermia treatments and is expected to provide a similar benefit for ablation therapy. Although this is primarily a review paper, some new data are included. These new data show that three antennas with 2.5 cm spacing at 45 W/channel and 10 min resulted in a volume of 89.8 cm(3) when operated synchronously, but only 53.4 cm(3) non-synchronously. Efficiency was 1.1 (synchronous) versus 0.7 (non-synchronous). MW systems, treatment planning, and image guidance continue to evolve to provide better tools and options for clinicians and patients in order to provide better approach and targeting optimisation with the goal of improved treatment for the patient.

Nanoparticle-mediated thermal therapy: evolving strategies for prostate cancer therapy

PURPOSE

Recent advances in nanotechnology have resulted in the manufacture of a plethora of nanoparticles of different sizes, shapes, core physicochemical properties and surface modifications that are being investigated for potential medical applications, particularly for the treatment of cancer. This review focuses on the therapeutic use of customised gold nanoparticles, magnetic nanoparticles and carbon nanotubes that efficiently generate heat upon electromagnetic (light and magnetic fields) stimulation after direct injection into tumours or preferential accumulation in tumours following systemic administration. This review will also focus on the evolving strategies to improve the therapeutic index of prostate cancer treatment using nanoparticle-mediated hyperthermia.

CONCLUSIONS

Nanoparticle-mediated thermal therapy is a new and minimally invasive tool in the armamentarium for the treatment of cancers. Unique challenges posed by this form of hyperthermia include the non-target biodistribution of nanoparticles in the reticuloendothelial system when administered systemically, the inability to visualise or quantify the global concentration and spatial distribution of these particles within tumours, the lack of standardised thermal modelling and dosimetry algorithms, and the concerns regarding their biocompatibility. Nevertheless, novel particle compositions, geometries, activation strategies, targeting techniques, payload delivery strategies, and radiation dose enhancement concepts are unique attributes of this form of hyperthermia that warrant further exploration. Capitalising on these opportunities and overcoming these challenges offers the possibility of seamless and logical translation of this nanoparticle-mediated hyperthermia paradigm from the bench to the bedside.

Microwave applicator for hyperthermia treatment on in vivo melanoma model

In this article, we evaluated a planar microwave applicator for in vivo superficial hyperthermia treatments on small tumors in the mouse mimicking treatments for human neoplasms. The design of the applicator, was challenged by the small dimensions of the tumors and unwanted diffusion of heating in the tumor-bearing animals. The required solution was to limit the penetration of microwaves in the depth of the tissue maintaining the full efficacy of hyperthermia. The study was firstly performed by computer simulations of SAR distribution inside a flat homogeneous phantom, considering various thicknesses of the integrated water bolus. Simulations, validated by the measurements, were also used to evaluate the impedance matching. Further tests were performed on homogeneous agar phantom to simulate the temperature distribution in the biological tissue and to preliminary assess the possible modality and schedule of microwave hyperthermia delivery. The in vivo experiments showed the evidence of direct microwave-induced heating and damage of the melanoma tissue in a range of penetration coherent both with computer simulations and phantom studies. The described approach appears perspective for designing limited-microwave-delivery applicators tailored for treatments of human superficial tumors and pre-tumoral lesions.

[Local treatment of prostate cancer using thermal-ablative energy]

Thermal and thermal-ablative procedures for treating prostate cancer have been investigated systematically since approximately 1980 (apart from some historical predecessors), and numerous experimental and clinical reports have been published on this subject. Various technologies have been used, including transurethral ablation of prostatic tissue using laser or microwave energy, interstitial application of laser or microwave energy, and inductive heating of previously implanted thermoseeds or injected magnetic nanoparticles in a magnetic field. For all of these procedures, clinical studies with a total of some 350 patients have been performed. However, the results cannot be judged correctly because of a lack of adequate control parameters for the older studies and inadequately short follow-up of all studies. Conclusions regarding treatment-related morbidity seem to be possible, with a generally positive impression and low rates of adverse effects. But before such results can be generalized, patient selection bias and the technology standards that existed when the studies were performed must be taken into consideration. Various papers are reviewed and summarized. In the author's opinion, the different options for thermal and thermal-ablative treatment of prostate cancer are very promising, but in light of the existing standard procedures, feasibility must not overrule reasonableness.

In vitro and in vivo evaluations of increased effective beam width for heat deposition using a split focus high intensity ultrasound (HIFU) transducer

PURPOSE

To develop a novel and efficient, in vitro method for characterizing temporal and spatial heat generation of focused ultrasound exposures, and evaluate this method to compare a split focus and conventional single focus high intensity focused ultrasound transducer.

MATERIALS AND METHODS

A HIFU tissue-mimicking phantom was validated by comparing respective temperature elevations generated in the phantoms and in murine tumors in vivo. The phantom was then used in combination with IR thermography to spatially and temporally characterize differences in low-level temperature elevation (e.g. 3-5 degrees C) produced by a single focus and split focus HIFU transducer, where the latter produces four simultaneous foci. In vivo experiments with heat sensitive liposomes containing doxorubicin were then carried out to determine if the larger beam width of the split focus transducer, compared to the single focus, could increase overall deployment of the drug from the liposome.

RESULTS

Temperature elevations generated in the HIFU phantom were not found to be different from those measured in vivo when compensating for disparities in attenuation coefficient and specific heat, and between the two transducers by increasing the energy deposition. Exposures with the split focus transducer provided significant increases in the area treated compared to the single focus, which then translated to significant increases in drug deposition in vivo.

CONCLUSIONS

Preliminary evidence was provided indicating the potential for using this novel technique for characterizing hyperthermia produced by focused ultrasound devices. Further development will be required for its suitability for correlating in vitro and in vivo outcomes.

Prostate thermal therapy with high intensity transurethral ultrasound: the impact of pelvic bone heating on treatment delivery

PURPOSE

This study was designed to assess pelvic bone temperature during typical treatment regimens of transurethral ultrasound thermal ablation of the prostate to establish guidelines for limiting bone heating.

METHODS

Treatment with transurethral planar, curvilinear, and sectored tubular applicators was simulated using an acoustic and biothermal pelvic model that accommodates applicator sweeping, boundary temperature control, and changes in perfusion and attenuation with thermal dose to more accurately model ultrasound energy penetration. The effects of various parameters including power and frequency (5-10 MHz) on bone heating were assessed for a range of prostate cross-sections (3-5 cm) and bone distances (1-3 cm).

RESULTS

All devices can produce significant bone heating (temperatures >50 degrees C, thermal dose >240 EM(43 degrees C)) without optimization of applied frequency or power for bone <3 cm from the prostate boundary. In small glands ( approximately 3 cm) increasing operating frequency of curvilinear and planar devices can increase bone temperatures, whereas the tubular applicator can be used at 10 MHz to avoid likely bone damage. In larger prostates (4-5 cm wide) increasing frequency reduces bone heating but can substantially increase treatment time. Lowering power can reduce bone temperature but may increase thermal dose by increasing treatment duration. All applicators can be used to treat glands 4-5 cm with limited bone heating by selecting appropriate power and frequency.

CONCLUSIONS

Pubic bone heating during ultrasound thermal therapy of the prostate can be substantial in certain situations. Successful realization of this therapy will require patient-specific treatment planning to optimally determine power and frequency in order to minimize bone heating.

An investigation of the use of transmission ultrasound to measure acoustic attenuation changes in thermal therapy

The potential of using a commercial ultrasound transmission imaging system to quantitatively monitor tissue attenuation changes after thermal therapy was investigated. The ultrasound transmission imaging system used, the AcoustoCam (Imperium Inc., MD) allows ultrasonic images to be captured using principles similar to that of a CCD-type camera that collects light. Ultrasound energy is focused onto a piezoelectric array by an acoustic lens system, creating a gray scale acoustic image. In this work, the pixel values from the acoustic images were assigned acoustic attenuation values by imaging polyacrylamide phantoms of varying known attenuation. After the calibration procedure, data from heated polyacrylamide/bovine serum albumin (BSA) based tissue-mimicking (TM) phantoms and porcine livers were acquired. Samples were heated in water at temperatures of 35, 45, 55, 65, and 75 degrees C for 1 h. Regions of interest were chosen in the images and acoustic attenuation values before and after heating were compared. An increase in ultrasound attenuation was found in phantoms containing BSA and in porcine liver. In the presence of BSA, attenuation in the TM phantom increased by a factor of 1.5, while without BSA no significant changes were observed. The attenuation of the porcine liver increased by up to a factor of 2.4, consistent with previously reported studies. The study demonstrates the feasibility of using a quantitative ultrasound transmission imaging system for monitoring thermal therapy.

Enhancement of tumor thermal therapy using gold nanoparticle–assisted tumor necrosis factor-α delivery

Tumor necrosis factor-alpha (TNF-alpha) is a potent cytokine with anticancer efficacy that can significantly enhance hyperthermic injury. However, TNF-alpha is systemically toxic, thereby creating a need for its selective tumor delivery. We used a newly developed nanoparticle delivery system consisting of 33-nm polyethylene glycol-coated colloidal gold nanoparticles (PT-cAu-TNF-alpha) with incorporated TNF-alpha payload (several hundred TNF-alpha molecules per nanoparticle) to maximize tumor damage and minimize systemic exposure to TNF-alpha. SCK mammary carcinomas grown in A/J mice were treated with 125 or 250 microg/kg PT-cAu-TNF-alpha alone or followed by local heating at 42.5 degrees C using a water bath for 60 minutes, 4 hours after nanoparticle injection. Increases in tumor growth delay were observed for both PT-cAu-TNF-alpha alone and heat alone, although the most dramatic effect was found in the combination treatment. Tumor blood flow was significantly suppressed 4 hours after an i.v. injection of free TNF-alpha or PT-cAu-TNF-alpha. Tumor perfusion, imaged by contrast enhanced ultrasonography, on days 1 and 5 after treatment revealed perfusion defects after the injection of PT-cAu-TNF-alpha alone and, in many regions, complete flow inhibition in tumors treated with combination treatment. The combination treatment of SCK tumors in vivo reduced the in vivo/in vitro tumor cell survival to 0.05% immediately following heating and to 0.005% at 18 hours after heating, suggesting vascular damage-mediated tumor cell killing. Thermally induced tumor growth delay was enhanced by pretreatment with TNF-alpha-coated gold nanoparticles when given i.v. at the proper dosage and timing.

Ultrawideband temperature-dependent dielectric properties of animal liver tissue in the microwave frequency range

The development of ultrawideband (UWB) microwave diagnostic and therapeutic technologies, such as UWB microwave breast cancer detection and hyperthermia treatment, is facilitated by accurate knowledge of the temperature- and frequency-dependent dielectric properties of biological tissues. To this end, we characterize the temperature-dependent dielectric properties of a representative tissue type-animal liver-from 0.5 to 20 GHz. Since discrete-frequency linear temperature coefficients are impractical and inappropriate for applications spanning wide frequency and temperature ranges, we propose a novel and compact data representation technique. A single-pole Cole-Cole model is used to fit the dielectric properties data as a function of frequency, and a second-order polynomial is used to fit the Cole-Cole parameters as a function of temperature. This approach permits rapid estimation of tissue dielectric properties at any temperature and frequency.