Current tumor ablation technologies: basic science and device review

Tissue Ablation: Applications and Perspectives

Tissue ablation techniques have emerged as a critical component of modern medical practice and biomedical research, offering versatile solutions for treating various diseases and disorders. Percutaneous ablation is minimally invasive and offers numerous advantages over traditional surgery, such as shorter recovery times, reduced hospital stays, and decreased healthcare costs. Intra-procedural imaging during ablation also allows precise visualization of the treated tissue while minimizing injury to the surrounding normal tissues, reducing the risk of complications. Here, the mechanisms of tissue ablation and innovative energy delivery systems are explored, highlighting recent advancements that have reshaped the landscape of clinical practice. Current clinical challenges related to tissue ablation are also discussed, underlining unmet clinical needs for more advanced material-based approaches to improve the delivery of energy and pharmacology-based therapeutics.

Microwave coagulation for liver metastases

BACKGROUND

Liver metastases (i.e. secondary hepatic malignancies) are significantly more common than primary liver cancer. Long-term survival after radical surgical treatment is approximately 50%. For people in whom resection for cure is not feasible, other treatments must be considered. One treatment option is microwave coagulation utilising electromagnetic waves. It involves placing an electrode into a lesion under ultrasound or computed tomography guidance.

OBJECTIVES

To evaluate the beneficial and harmful effects of microwave coagulation versus no intervention, other ablation methods, or systemic treatments in people with liver metastases regardless of the location of the primary tumour.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest date of search was 14 April 2023.

SELECTION CRITERIA

Randomised clinical trials assessing beneficial or harmful effects of microwave coagulation and its comparators in people with liver metastases, irrespective of the location of the primary tumour. We included trials no matter the outcomes reported.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methodological procedures. Our primary outcomes were: all-cause mortality at the last follow-up and time to mortality; health-related quality of life (HRQoL); and any adverse events or complications. Our secondary outcomes were: cancer mortality; disease-free survival; failure to clear liver metastases; recurrence of liver metastases; time to progression of liver metastases; and tumour response measures. We used risk ratios (RR) and hazard ratios (HR) with 95% confidence intervals (CI) to present the results. Two review authors independently extracted data and assessed the risk of bias using the Cochrane RoB 1 tool. We used GRADE methodology to assess the certainty of the evidence.

MAIN RESULTS

Three randomised clinical trials fulfilled the inclusion criteria. The control interventions differed in the three trials; therefore, meta-analyses were not possible. The trials were at high risk of bias. The certainty of evidence of the assessed outcomes in the three comparisons was very low. Data on our prespecified outcomes were either missing or not reported. Microwave coagulation plus conventional transarterial chemoembolisation (TACE) versus conventional TACE alone One trial, conducted in China, randomised 50 participants (mean age 60 years, 76% males) with liver metastases from various primary sites. Authors reported that the follow-up period was at least one month. The trial reported adverse events or complications in the experimental group only and for tumour response measures. There were no dropouts in the trial. The trial did not report on any other outcomes. Microwave ablation versus conventional surgery One trial, conducted in Japan, randomised 40 participants (mean age 61 years, 53% males) with multiple liver metastases of colorectal cancer. Ten participants were excluded after randomisation (six from the experimental and four from the control group); thus, the trial analyses included 30 participants. Follow-up was three years. The reported number of deaths from all causes was 9/14 included participants in the microwave group versus 12/16 included participants in the conventional surgery group. The mean overall survival was 27 months in the microwave ablation and 25 months in the conventional surgery group. The three-year overall survival was 14% with microwave ablation and 23% with conventional surgery, resulting in an HR of 0.91 (95% CI 0.39 to 2.15). The reported frequency of adverse events or complications was comparable between the two groups, except for the required blood transfusion, which was more common in the conventional surgery group. There was no intervention-related mortality. Disease-free survival was 11.3 months in the microwave ablationgroup and 13.3 months in the conventional surgery group. The trial did not report on HRQoL. Microwave ablation versus radiofrequency ablation One trial, conducted in Germany, randomised 50 participants (mean age 62.8 years, 46% males) who were followed for 24 months. Two-year mortality showed an RR of 0.62 (95% CI 0.26 to 1.47). The trial reported that, by two years, 76.9% of participants in the microwave ablationgroup and 62.5% of participants in the radiofrequency ablation group survived (HR 0.63, 95% CI 0.23 to 1.73). The trial reported no deaths or major complications during the procedures in either group. There were two minor complications only in the radiofrequency ablation group (RR 0.19, 95% CI 0.01 to 3.67). The trial reported technical efficacy in 100% of procedures in both groups. Distant recurrence was reported for 10 participants in the microwave ablation group and nine participants in the radiofrequency ablation group (RR 1.03, 95% CI 0.50 to 2.08). No participant in the microwave ablation group demonstrated local progression at 12 months, while that occurred in two participants in the radiofrequency ablation group (RR 0.19, 95% CI 0.01 to 3.67). The trial did not report on HRQoL. One trial reported partial support by Medicor (MMS Medicor Medical Supplies GmbH, Kerpen, Germany) for statistical analysis. The remaining two trials did not provide information on funding. We identified four ongoing trials.

AUTHORS' CONCLUSIONS

The evidence is very uncertain about the effect of microwave ablation in addition to conventional TACE compared with conventional TACE alone on adverse events or complications. We do not know if microwave ablation compared with conventional surgery may have little to no effect on all-cause mortality. We do not know the effect of microwave ablation compared with radiofrequency ablation on all-cause mortality and adverse events or complications either. Data on all-cause mortality and time to mortality, HRQoL, adverse events or complications, cancer mortality, disease-free survival, failure to clear liver metastases, recurrence of liver metastases, time to progression of liver metastases, and tumour response measures were either insufficient or were lacking. In light of the current inconclusive evidence and the substantial gaps in data, the pursuit of additional good-quality, large randomised clinical trials is not only justified but also essential to elucidate the efficacy and comparative benefits of microwave ablation in relation to various interventions for liver metastases. The current version of the review, in comparison to the previous one, incorporates two new trials in two additional microwave ablation comparisons: 1. in addition to conventional TACE versus conventional TACE alone and 2. versus radiofrequency ablation.

New Insights on Liver-Directed Therapies in Hepatocellular Carcinoma

The incidence of hepatocellular carcinoma (HCC) has been increasing over the past decades, but improvements in systemic and locoregional therapies is increasing survival. Current locoregional treatment options include ablation, transarterial chemoembolization (TACE), transarterial radioembolization (TARE), and stereotactic body radiotherapy (SBRT). There is ongoing research regarding the combination of systemic and local therapies to maximize treatment effect as well as in new non-invasive, image-guided techniques such as histotripsy. There is also active research in optimizing the delivery of therapy to tumors via nanostructures and viral-vector-mediated gene therapies. In many cases, patients require a combination of therapies to achieve tumor control and prolong survival. This article provides an overview of the most common liver-directed therapies for HCC as well as insight into more recent advances in personalized medicine and emerging techniques.

A review on radiofrequency, laser, and microwave ablations and their thermal monitoring through fiber Bragg gratings

Thermal ablation of tumors aims to apply extreme temperatures inside the target tissue to achieve substantial tumor destruction in a minimally invasive manner. Several techniques are comprised, classified according to the type of energy source. However, the lack of treatment selectivity still needs to be addressed, potentially causing two risks: i) incomplete tumor destruction and recurrence, or conversely, ii) damage of the surrounding healthy tissue. Therefore, the research herein reviewed seeks to develop sensing systems based on fiber Bragg gratings (FBGs) for thermal monitoring inside the lesion during radiofrequency, laser, and microwave ablation. This review shows that, mainly thanks to multiplexing and minimal invasiveness, FBGs provide an optimal sensing solution. Their temperature measurements are the feedback to control the ablation process and allow to investigate different treatments, compare their outcomes, and quantify the impact of factors such as proximity to thermal probe and blood vessels, perfusion, and tissue type.

Combining energy-based focal ablation and immune checkpoint inhibitors: preclinical research and clinical trials

Energy-based focal therapy (FT) uses targeted, minimally invasive procedures to destroy tumors while preserving normal tissue and function. There is strong emerging interest in understanding how systemic immunity against the tumor can occur with cancer immunotherapy, most notably immune checkpoint inhibitors (ICI). The motivation for combining FT and ICI in cancer management relies on the synergy between the two different therapies: FT complements ICI by reducing tumor burden, increasing objective response rate, and reducing side effects of ICI; ICI supplements FT by reducing local recurrence, controlling distal metastases, and providing long-term protection. This combinatorial strategy has shown promising results in preclinical study (since 2004) and the clinical trials (since 2011). Understanding the synergy calls for understanding the physics and biology behind the two different therapies with distinctive mechanisms of action. In this review, we introduce different types of energy-based FT by covering the biophysics of tissue-energy interaction and present the immunomodulatory properties of FT. We discuss the basis of cancer immunotherapy with the emphasis on ICI. We examine the approaches researchers have been using and the results from both preclinical models and clinical trials from our exhaustive literature research. Finally, the challenges of the combinatory strategy and opportunities of future research is discussed extensively.

Analysis of electromagnetic response of cells and lipid membranes using a model-free method

Electromagnetic radiation (EMR) is omnipresent on earth and may interact with the biological systems in diverse manners. But the scope and nature of such interactions remain poorly understood. In this study, we have measured the permittivity of cells and lipid membranes over the EMR frequency range of 20 Hz to 4.35 × 10¹⁰ Hz. To identify EMR frequencies that display physically intuitive permittivity features, we have developed a model-free method that relies on a potassium chloride reference solution of direct-current (DC) conductivity equal to that of the target sample. The dielectric constant, which reflects the capacity to store energy, displays a characteristic peak at 10⁵-10⁶ Hz. The dielectric loss factor, which represents EMR absorption, is markedly enhanced at 10⁷-10⁹ Hz. The fine characteristic features are influenced by the size and composition of these membraned structures. Mechanical disruption results in abrogation of these characteristic features. Enhanced energy storage at 10⁵-10⁶ Hz and energy absorption at 10⁷-10⁹ Hz may affect certain membrane activity relevant to cellular function.

Thermochromic Tissue-Mimicking Phantoms for Thermal Ablation Based on Polyacrylamide Gel

In recent years, thermal ablation has played an increasingly important role in treating various tumors in the clinic. A practical thermochromic phantom model can provide a favorable platform for clinical thermotherapy training of young physicians or calibration and optimization of thermal devices without risk to animals or human participants. To date, many tissue-mimicking thermal phantoms have been developed and are well liked, especially the polyacrylamide gel (PAG)-based phantoms. This review summarizes the PAG-based phantoms in the field of thermotherapy, details their advantages and disadvantages and provides a direction for further optimization. The relevant physical parameters (such as electrical, acoustic, and thermal properties) of these phantoms are also presented in this review, which can assist operators in a deeper understanding of these phantoms and selection of the proper recipes for phantom fabrication.

Use of percutaneous microwave ablation in the treatment of retroperitoneal neoplasia in three dogs

CASE DESCRIPTION

3 dogs with retroperitoneal masses (2 renal and 1 located near the diaphragm) were treated by percutaneous microwave ablation (MWA).

CLINICAL FINDINGS

Dogs between 11 and 13 years of age weighing between 13.7 and 43.8 kg had either a renal mass (n = 2) or a mass located in the caudodorsal aspect of the retroperitoneal space near the right side of the diaphragm (1). Cytology revealed that one of the renal masses and the mass located near the diaphragm were malignant neoplasias. Findings on cytologic evaluation of a sample of the other renal mass was nondiagnostic. Maximum mass diameters ranged between 1.4 and 2.5 cm.

TREATMENT AND OUTCOME

All dogs were treated by percutaneous MWA. Probes were directed into tumors by use of ultrasound and CT guidance, and microwave energy was applied to each mass. Findings on imaging of each mass following MWA was consistent with successful treatment. No intraprocedural or major postprocedural complications occurred, and all dogs were discharged from the hospital within 3 days of treatment. Two dogs died at 3 and 21 months after MWA with no known local recurrence; 1 dog was still alive 64 months after treatment.

CLINICAL RELEVANCE

Although the indications for MWA in the treatment of neoplasia in companion animals are limited, the outcomes of dogs in the present report provided preliminary evidence that percutaneous MWA can be safely used to effectively treat retroperitoneal neoplasia. This procedure was successfully performed with image guidance in all 3 dogs.

Radiologic-pathologic analysis of increased ethanol localization and ablative extent achieved by ethyl cellulose

Ethanol provides a rapid, low-cost ablative solution for liver tumors with a small technological footprint but suffers from uncontrolled diffusion in target tissue, limiting treatment precision and accuracy. Incorporating the gel-forming polymer ethyl cellulose to ethanol localizes the distribution. The purpose of this study was to establish a non-invasive methodology based on CT imaging to quantitatively determine the relationship between the delivery parameters of the EC-ethanol formulation, its distribution, and the corresponding necrotic volume. The relationship of radiodensity to ethanol concentration was characterized with water-ethanol surrogates. Ex vivo EC-ethanol ablations were performed to optimize the formulation (n = 6). In vivo ablations were performed to compare the optimal EC-ethanol formulation to pure ethanol (n = 6). Ablations were monitored with CT and ethanol distribution volume was quantified. Livers were removed, sectioned and stained with NADH-diaphorase to determine the ablative extent, and a detailed time-course histological study was performed to assess the wound healing process. CT imaging of ethanol-water surrogates demonstrated the ethanol concentration-radiodensity relationship is approximately linear. A concentration of 12% EC in ethanol created the largest distribution volume, more than eight-fold that of pure ethanol, ex vivo. In vivo, 12% EC-ethanol was superior to pure ethanol, yielding a distribution volume three-fold greater and an ablation zone six-fold greater than pure ethanol. Finally, a time course histological evaluation of the liver post-ablation with 12% EC-ethanol and pure ethanol revealed that while both induce coagulative necrosis and similar tissue responses at 1-4 weeks post-ablation, 12% EC-ethanol yielded a larger ablation zone. The current study demonstrates the suitability of CT imaging to determine distribution volume and concentration of ethanol in tissue. The distribution volume of EC-ethanol is nearly equivalent to the resultant necrotic volume and increases distribution and necrosis compared to pure ethanol.

Focused ultrasound radiosensitizes human cancer cells by enhancement of DNA damage

Purpose

High-intensity focused ultrasound (HIFU/FUS) has expanded as a noninvasive quantifiable option for hyperthermia (HT). HT in a temperature range of 40–47 °C (thermal dose CEM43 ≥ 25) could work as a sensitizer to radiation therapy (RT). Here, we attempted to understand the tumor radiosensitization effect at the cellular level after a combination treatment of FUS+RT.

Methods

An in vitro FUS system was developed to induce HT at frequencies of 1.147 and 1.467 MHz. Human head and neck cancer (FaDU), glioblastoma (T98G), and prostate cancer (PC-3) cells were exposed to FUS in ultrasound-penetrable 96-well plates followed by single-dose X‑ray irradiation (10 Gy). Radiosensitizing effects of FUS were investigated by cell metabolic activity (WST‑1 assay), apoptosis (annexin V assay, sub-G1 assay), cell cycle phases (propidium iodide staining), and DNA double-strand breaks (γH2A.X assay).

Results

The FUS intensities of 213 (1.147 MHz) and 225 W/cm² (1.467 MHz) induced HT for 30 min at mean temperatures of 45.20 ± 2.29 °C (CEM43 = 436 ± 88) and 45.59 ± 1.65 °C (CEM43 = 447 ± 79), respectively. FUS improves the effect of RT significantly by reducing metabolic activity in T98G cells 48 h (RT: 96.47 ± 8.29%; FUS+RT: 79.38 ± 14.93%; p = 0.012) and in PC-3 cells 72 h (54.20 ± 10.85%; 41.01 ± 11.17%; p = 0.016) after therapy, but not in FaDu cells. Mechanistically, FUS+RT leads to increased apoptosis and enhancement of DNA double-strand breaks compared to RT alone in T98G and PC-3 cells.

Conclusion

Our in vitro findings demonstrate that FUS has good potential to sensitize glioblastoma and prostate cancer cells to RT by mainly enhancing DNA damage.

Supplementary Information

The online version of this article (10.1007/s00066-021-01774-5) contains supplementary material, which is available to authorized users.

Oxidative Effects during Irreversible Electroporation of Melanoma Cells-In Vitro Study

Irreversible electroporation (IRE) is today used as an alternative to surgery for the excision of cancer lesions. This study aimed to investigate the oxidative and cytotoxic effects the cells undergo during irreversible electroporation using IRE protocols. To do so, we used IRE-inducing pulsed electric fields (PEFs) (eight pulses of 0.1 ms duration and 2-4 kV/cm intensity) and compared their effects to those of PEFs of intensities below the electroporation threshold (eight pulses, 0.1 ms, 0.2-0.4 kV/cm) and the PEFs involving elongated pulses (eight pulses, 10 ms, 0.2-0.4 kV/cm). Next, to follow the morphology of the melanoma cell membranes after treatment with the PEFs, we analyzed the permeability and integrity of their membranes and analyzed the radical oxygen species (ROS) bursts and the membrane lipids' oxidation. Our data showed that IRE-induced high cytotoxic effect is associated both with irreversible cell membrane disruption and ROS-associated oxidation, which is occurrent also in the low electric field range. It was shown that the viability of melanoma cells characterized by similar ROS content and lipid membrane oxidation after PEF treatment depends on the integrity of the membrane system. Namely, when the effects of the PEF on the membrane are reversible, aside from the high level of ROS and membrane oxidation, the cell does not undergo cell death.

An interventional image-guided microdevice implantation and retrieval method for in-vivo drug response assessment

PURPOSE

Recently developed implantable microdevices can perform multi-drug response assessment of cancer drugs in-vivo, with potential to develop highly optimized personalized cancer treatment strategies. However, minimally invasive/interventional image-guided methods of in-vivo microdevice implantation, securement, and retrieval are needed for broad clinical translation. Here we demonstrate proof-of-concept of an interventional microdevice implantation and retrieval method for personalized drug response assessment, using ex-vivo phantom, ex-vivo tissue, and in-vivo murine models.

METHODS

A method for minimally-invasive microdevice implantation and retrieval was developed, by which a custom-prototyped 6 mm retrievable microdevice can be implanted into a live tumor, deliver drugs into 10 discrete regions of adjacent tissue, and retrieved along with the adjacent drug-exposed tissue with a custom-prototyped retrieval needle device to allow in-vivo multi-drug response assessment. Computed tomography (CT) and ultrasound (US)-guided minimally invasive microdevice implantation and retrieval were tested in ex-vivo phantom and tissue models. Successful retrieval was defined as retrieval of the microdevice and adjacent core phantom/tissue sample containing at least 4/10 drug delivery sites. Subsequently, 10 implantation and retrieval trials in phantom models were performed using bi-axial and tri-axial retrieval needles; success rates were calculated and compared using a two-proportion z-test and the number of successfully retrieved drug release sites per microdevice was calculated and compared using a one-tailed independent t-test. Finally, five microdevices, each containing ten reservoirs preloaded with chemotherapy agent Doxorubicin, were implanted into mouse tumors in-vivo, secured for 24-h during drug release, and microdevice/tissue retrieval was performed under ultrasound guidance. Fluorescence microscopy of the retrieved tissue was used to confirm drug delivery and apoptosis staining assessed in-vivo tissue response; correlation of drug release and apoptosis staining were used to assess in-vivo drug efficacy.

RESULTS

Image-guided microdevice implantation and retrieval were successful in ex-vivo phantom and tissue models with both US and CT guidance. Bi-axial retrieval success rate was significantly higher than triaxial retrieval in ex-vivo phantom trials (90% vs 50%, z = 1.95, P = 0.026), and had nonsignificantly higher number of retrieved drug-release sites per microdevice (8.3 vs 7.0, t = 1.37, P = 0.097). Bi-axial retrieval was successful in all five in-vivo mouse tumor models, and allowed in-vivo drug response assessment at up to ten discrete drug delivery sites per microdevice. An average of 6.8/10 discrete tumor sites containing micro-doses of delivered drug were retrieved per in-vivo attempt (min 5, max 10, std 1.93). Tissue regions of drug delivery, as assessed with fluorescent Doxorubicin drug signal, correlated with regions of apoptosis staining in all in-vivo models, indicating drug efficacy. No bleeding, microdevice migration, or other complications were noted during implantation, 24-h observation, or retrieval.

CONCLUSIONS

The demonstrated image-guided minimally invasive microdevice implantation and retrieval method is similar to routine outpatient biopsy procedures, obviates the need for surgery, and can be performed at varying depths under CT and/or US guidance. There is potential for this method to enable clinical translation of in-vivo personalized drug response assessment/prediction in a much larger number of patients than currently possible.

Veterinary Clinics: Tumor Ablation

Over the past decade, interventional oncology techniques have become integrated into the treatment plans of companion animals with cancer on a regular basis. Although procedures such as stenting are performed commonly, other less frequently utilized techniques for locoregional therapy, such as embolization and ablation, are emerging and demonstrating promise. Tumor ablation techniques are categorized into two subgroups: chemical ablation and energy-based ablation. Increased utilization of ablation will allow for the determination of specific indications and evaluation of outcomes for these techniques.

Prediction of Gold Nanoparticle and Microwave-Induced Hyperthermia Effects on Tumor Control via a Simulation Approach

Hyperthermia acts as a powerful adjuvant to radiation therapy and chemotherapy. Recent advances show that gold nanoparticles (Au-NPs) can mediate highly localized thermal effects upon interaction with laser radiation. The purpose of the present study was to investigate via in silico simulations the mechanisms of Au-NPs and microwave-induced hyperthermia, in correlation to predictions of tumor control (biological endpoints: tumor shrinkage and cell death) after hyperthermia treatment. We also study in detail the dependence of the size, shape and structure of the gold nanoparticles on their absorption efficiency, and provide general guidelines on how one could modify the absorption spectrum of the nanoparticles in order to meet the needs of specific applications. We calculated the hyperthermia effect using two types of Au-NPs and two types of spherical tumors (prostate and melanoma) with a radius of 3 mm. The plasmon peak for the 30 nm Si-core Au-coated NPs and the 20 nm Au-NPs was found at 590 nm and 540 nm, respectively. Considering the plasmon peaks and the distribution of NPs in the tumor tissue, the induced thermal profile was estimated for different intervals of time. Predictions of hyperthermic cell death were performed by adopting a three-state mathematical model, where “three-state” includes (i) alive, (ii) vulnerable, and (iii) dead states of the cell, and it was coupled with a tumor growth model. Our proposed methodology and preliminary results could be considered as a proof-of-principle for the significance of simulating accurately the hyperthermia-based tumor control involving the immune system. We also propose a method for the optimization of treatment by overcoming thermoresistance by biological means and specifically through the targeting of the heat shock protein 90 (HSP90), which plays a critical role in the thermotolerance of cells and tissues.

Unintended Consequences of Systemic and Ablative Oncologic Therapy in the Abdomen and Pelvis

Human cancers are genetically complex and diverse. Although advances in oncologic therapy aim to define and target unique steps in carcinogenesis, oncologists often rely on less discriminate anticancer therapies that have consequences for normal tissues. Even many of the so-called targeted therapies currently employed can adversely affect normal cells, leading to complications that necessitate dose reductions or cessation of specific therapies. This article explores the unintended consequences of currently employed systemic and ablative anticancer therapies that might manifest at imaging examinations of the abdomen and pelvis, including cytotoxic, molecular targeted, and immunologic agents; ablation; and hematopoietic stem cell transplant. Each of these treatments can have both major and minor unintended effects in the targeted organ(s), in local or adjacent structures, or at distant sites. Timely detection and reporting of adverse consequences of anticancer therapies by the astute imager can result in critical treatment modifications and/or lifesaving interventions; therefore, knowledge of these unintended effects is paramount for radiologists interpreting the results of imaging examinations in cancer patients. ^©RSNA, 2018.

Metal-Assisted and Microwave-Accelerated Decrystallization: An Alternative Approach to Potential Treatment of Crystal Deposition Diseases

Gout is a painful and prevalent crystal deposition disease caused by the overproduction of Uric Acid (UA) in the body and the atypical deposition in human synovial joints as Monosodium Urate Monohydrate (MSUM). Conventional treatments, such as NSAIDs, cyclooxygenase-2 inhibitors, and systemic glucocorticoids often present harmful side-effects and are short-lived. Long-term therapies including xanthine oxidase inhibitors and the use of uricosuric agents have been developed and aim to lower the UA serum levels in the body. As regards to post-crystals deposition, our research laboratory recently proposed and demonstrated the use of the Metal-Assisted and Microwave-Accelerated Decrystallization (MAMAD) technique for the breakdown of organic and biological crystals on planar surfaces. The MAMAD technique is based on the combined use of microwave heating and Au NPs in solution. The interactions of the Au NPs with microwave's electromagnetic field result in an increase in the kinetic energy of Au NPs, and subsequently, an increase in the collisions with target crystals placed on planar surfaces leading to rapid crystal breakdown. In this regard, our laboratory aims to develop the MAMAD technique as an alternative treatment for crystal deposition diseases, particularly gout, with minimal invasion and side-effects as compared to current treatments. In this review article, we will summarize our previous findings and provide additional data detailing the effectiveness of the MAMAD technique as a rapid and efficient method for the breakdown of gout related crystals and L-alanine crystals (a model crystal).

Evaluation of a tissue-mimicking thermochromic phantom for radiofrequency ablation

PURPOSE

This work describes the characterization and evaluation of a tissue-mimicking thermochromic phantom (TMTCP) for direct visualization and quantitative determination of temperatures during radiofrequency ablation (RFA).

METHODS

TMTCP material was prepared using polyacrylamide gel and thermochromic ink that permanently changes color from white to magenta when heated. Color vs temperature calibration was generated in matlab by extracting RGB color values from digital photographs of phantom standards heated in a water bath at 25-75 °C. RGB and temperature values were plotted prior to curve fitting in mathematica using logistic functions of form f(t) = a + b/(1 + e((c(t-d)))), where a, b, c, and d are coefficients and t denotes temperature. To quantify temperatures based on TMTCP color, phantom samples were heated to temperatures blinded to the investigators, and two methods were evaluated: (1) visual comparison of sample color to the calibration series and (2) in silico analysis using the inverse of the logistic functions to convert sample photograph RGB values to absolute temperatures. For evaluation of TMTCP performance with RFA, temperatures in phantom samples and in a bovine liver were measured radially from an RF electrode during heating using fiber-optic temperature probes. Heating and cooling rates as well as the area under the temperature vs time curves were compared. Finally, temperature isotherms were generated computationally based on color change in bisected phantoms following RFA and compared to temperature probe measurements.

RESULTS

TMTCP heating resulted in incremental, permanent color changes between 40 and 64 °C. Visual and computational temperature estimation methods were accurate to within 1.4 and 1.9 °C between 48 and 67 °C, respectively. Temperature estimates were most accurate between 52 and 62 °C, resulting in differences from actual temperatures of 0.6 and 1.6 °C for visual and computational methods, respectively. Temperature measurements during RFA using fiber-optic probes matched closely with maximum temperatures predicted by color changes in the TMTCP. Heating rate and cooling rate, as well as the area under the temperature vs time curve were similar for TMTCP and ex vivo liver.

CONCLUSIONS

The TMTCP formulated for use with RFA can be used to provide quantitative temperature information in mild hyperthermic (40-45 °C), subablative (45-50 °C), and ablative (>50 °C) temperature ranges. Accurate visual or computational estimates of absolute temperatures and ablation zone geometry can be made with high spatial resolution based on TMTCP color. As such, the TMTCP can be used to assess RFA heating characteristics in a controlled, predictable environment.

Decrystallization of Crystals Using Gold "Nano-Bullets" and the Metal-Assisted and Microwave-Accelerated Decrystallization Technique

Gout is caused by the overproduction of uric acid and the inefficient metabolism of dietary purines in humans. Current treatments of gout, which include anti-inflammatory drugs, cyclooxygenase-2 inhibitors, and systemic glucocorticoids, have harmful side-effects. Our research laboratory has recently introduced an innovative approach for the decrystallization of biological and chemical crystals using the Metal-Assisted and Microwave-Accelerated Evaporative Decrystallization (MAMAD) technique. In the MAMAD technique, microwave energy is used to heat and activate gold nanoparticles that behave as “nano-bullets” to rapidly disrupt the crystal structure of biological crystals placed on planar surfaces. In this study, crystals of various sizes and compositions were studied as models for tophaceous gout at different stages (i.e., uric acid as small crystals (~10–100 μm) and l-alanine as medium (~300 μm) and large crystals (~4400 μm). Our results showed that the use of the MAMAD technique resulted in the reduction of the size and number of uric acid and l-alanine crystals up to >40% when exposed to intermittent microwave heating (up to 20 W power at 8 GHz) in the presence of 20 nm gold nanoparticles up to 120 s. This study demonstrates that the MAMAD technique can be potentially used as an alternative therapeutic method for the treatment of gout by effective decrystallization of large crystals, similar in size to those that often occur in gout.

Colorectal Cancer Liver Metastases: Biopsy of the Ablation Zone and Margins Can Be Used to Predict Oncologic Outcome

Purpose To establish the prognostic value of biopsy of the central and marginal ablation zones for time to local tumor progression (LTP) after radiofrequency (RF) ablation of colorectal cancer liver metastasis (CLM). Materials and Methods A total of 47 patients with 67 CLMs were enrolled in this prospective institutional review board-approved and HIPAA-compliant study between November 2009 and August 2012. Mean tumor size was 2.1 cm (range, 0.6-4.3 cm). Biopsy of the center and margin of the ablation zone was performed immediately after RF ablation (mean number of biopsy samples per ablation zone, 1.9) and was evaluated for the presence of viable tumor cells. Samples containing tumor cells at morphologic evaluation were further interrogated with immunohistochemistry and were classified as either positive, viable tumor (V) or negative, necrotic (N). Minimal ablation margin size was evaluated in the first postablation CT study performed 4-8 weeks after ablation. Variables were evaluated as predictors of time to LTP with the competing-risks model (uni- and multivariate analyses). Results Technical effectiveness was evident in 66 of 67 (98%) ablated lesions on the first contrast material-enhanced CT images at 4-8-week follow-up. The cumulative incidence of LTP at 12-month follow-up was 22% (95% confidence interval [CI]: 12, 32). Samples from 16 (24%) of 67 ablation zones were classified as viable tumor. At univariate analysis, tumor size, minimal margin size, and biopsy results were significant in predicting LTP. When these variables were subsequently entered in a multivariate model, margin size of less than 5 mm (P < .001; hazard ratio [HR], 6.7) and positive biopsy results (P = .008; HR, 3.4) were significant. LTP within 12 months after RF ablation was noted in 3% (95% CI: 0, 9) of necrotic CLMs with margins of at least 5 mm. Conclusion Biopsy proof of complete tumor ablation and minimal ablation margins of at least 5 mm are independent predictors of LTP and yield the best oncologic outcomes. (©) RSNA, 2016.

The Emprint™ Ablation System with Thermosphere™ Technology: One of the Newer Next-Generation Microwave Ablation Technologies

Microwave ablation is a recent development in the field of tumor ablation that uses electromagnetic waves to establish a microwave near-field with direct tissue heating. Some of the limitations of the earlier generation devices had been unpredictable size and shape of the ablation zones with changes in the surrounding tissue environment as well as differences across various different tissue types. The Emprint Ablation System with Thermosphere Technology (Covidien, Boulder, CO) is the most recent generation ablation system that attempts to produce predictable large spherical zones of ablation despite varying tissue environments across different tissue types such as liver, lung, and bone to name a few. This article will discuss these recent device developments as well as review some basic microwave characteristics.

Photothermal ablation of bone metastasis of breast cancer using PEGylated multi-walled carbon nanotubes

This study investigates therapeutic efficacy of photothermal therapy (PTT) in an orthotropic xenograft model of bone metastasis of breast cancer. The near-infrared (NIR) irradiation on Multi-Walled Carbon Nanotubes (MWNTs) resulted in a rapid heat generation which increased with the MWNTs concentration up to 100 μg/ml. MWNTs alone exhibited no toxicity, but inclusion of MWNTs dramatically decreased cell viability when combined with laser irradiation. Thermographic observation revealed that treatment with 10 μg MWNTs followed by NIR laser irradiation resulted in a rapid increase in temperature up to 73.4±11.98 °C in an intraosseous model of bone metastasis of breast cancer. In addition, MWNTs plus NIR laser irradiation caused a remarkably greater suppression of tumor growth compared with treatment with either MWNTs injection or NIR irradiation alone, significantly reducing the amount of tumor-induced bone destruction. All these demonstrate the efficacy of PTT with MWNTs for bone metastasis of breast cancer.

Effect of Nonparallel Placement of In-Circle Bipolar Radiofrequency Ablation Probes on Volume of Tissue Ablated With Heat Sink

Objectives. Percutaneous bipolar radiofrequency ablation (RFA) is a minimally invasive technique for treating liver tumors. It is not always possible to insert the bipolar probes parallel to each other on either side of tumor, since it restricts maneuverability away from vital structures or ablate certain tumor shape. Therefore, we investigated how nonparallel placement of probes affected ablation. Methods. Bipolar RFA in parallel and in divergent positions were submerged in tissue model (800 mL egg white) at 37°C and ablated. Temperature probes, T1 and T2 were placed 8.00 mm below the tip of the probes, T3 in between the probe coil elements and T4 and T5 at water inlet and outlet, respectively. Both models with heat sink (+HS) and without (−HS) were investigated. Results. The mean ablated tissue volume, mass, density and height increased linearly with unit angle increase for −HS model. With +HS, a smaller increase in mean volume and mass, a slightly greater increase in mean density but a reduction in height of tissue was seen. The mean ablation time and duration of maximum temperature with +HS was slightly larger, compared with −HS, while −HS ablated at a slightly higher temperature. The heat sink present was minimal for probes in parallel position compared to nonparallel positions. Conclusion. Divergence from parallel insertion of bipolar RFA probes increased the mean volume, mass, and density of tissue ablated. However, the presence of large heat sinks may limit the application of this technique, when tumors border on larger vessels.

Influence of nesting shell size on brightness longevity and resistance to ultrasound-induced dissolution during enhanced B-mode contrast imaging

This study aims to bridge the gap between transport mechanisms of an improved ultrasound contrast agent (UCA) and its resulting behavior in a clinical imaging study. Phospholipid-shelled microbubbles nested within the aqueous core of a polymer microcapsule are examined for their use and feasibility as an improved UCA. The nested formulation provides contrast comparable to traditional formulations, specifically an SF6 microbubble coated by a DSPC PEG-3000 monolayer, with the advantage that contrast persists at least nine times longer in a mock clinical, in vitro setting. The effectiveness of the sample was measured using a contrast ratio in units of decibels (dB) which compares the brightness of the nested microbubbles to a reference value of a phantom tissue mimic. During a 40min imaging study, six nesting formulations with average outer capsule diameters of 1.95, 2.53, 5.55, 9.95, 14.95, and 20.51μm reached final contrast ratio values of 0.25, 2.35, 3.68, 4.51, 5.93, and 8.00dB, respectively. The starting contrast ratio in each case was approximately 8dB and accounts for the brightness attributed to the nesting shell. As compared with empty microcapsules (no microbubbles nested within), enhancement of the initial contrast ratio increased systematically with decreasing microcapsule size. The time required to reach a steady state in the temporal contrast ratio profile also varied with microcapsule diameter and was found to be 420s for each of the four smallest shell diameters and 210s and 150s, respectively, for the largest two shell diameters. All nested formulations were longer-lived and gave higher final contrast ratios than a control sample comprising un-nested, but otherwise equivalent, microbubbles. Specifically, the contrast ratio of the un-nested microbubbles decreased to a negative value after 4min of continuous ultrasound exposure with complete disappearance of the microbubbles after 15min whereas all nested formulations maintained positive contrast ratio values for the duration of the 40min trial. The results are consistent with two distinct stages of gas transport: in the first stage, passive diffusion occurs under ambient conditions across the microbubble monolayer within the first few minutes after formulation until the aqueous interior of the microcapsule is saturated with gas; in the second stage ultrasound drives additional gas dissolution even further due to pressure modulation. It is important to understand the chemistry and transport mechanisms of this contrast agent under the influence of ultrasound to attain better perspicacity for enhanced applications in imaging. Results from this study will facilitate future preclinical studies and clinical applications of nested microbubbles for therapeutic and diagnostic imaging.

A histological evaluation and in vivo assessment of intratumoral near infrared photothermal nanotherapy-induced tumor regression

PURPOSE

Nanoparticle (NP)-enabled near infrared (NIR) photothermal therapy has realized limited success in in vivo studies as a potential localized cancer therapy. This is primarily due to a lack of successful methods that can prevent NP uptake by the reticuloendothelial system, especially the liver and kidney, and deliver sufficient quantities of intravenously injected NPs to the tumor site. Histological evaluation of photothermal therapy-induced tumor regression is also neglected in the current literature. This report demonstrates and histologically evaluates the in vivo potential of NIR photothermal therapy by circumventing the challenges of intravenous NP delivery and tumor targeting found in other photothermal therapy studies.

METHODS

Subcutaneous Cal 27 squamous cell carcinoma xenografts received photothermal nanotherapy treatments, radial injections of polyethylene glycol (PEG)-ylated gold nanorods and one NIR 785 nm laser irradiation for 10 minutes at 9.5 W/cm(2). Tumor response was measured for 10-15 days, gross changes in tumor size were evaluated, and the remaining tumors or scar tissues were excised and histologically analyzed.

RESULTS

The single treatment of intratumoral nanorod injections followed by a 10 minute NIR laser treatment also known as photothermal nanotherapy, resulted in ~100% tumor regression in ~90% of treated tumors, which was statistically significant in a comparison to the average of all three control groups over time (P<0.01).

CONCLUSION

Photothermal nanotherapy, or intratumoral nanorod injections followed by NIR laser irradiation of tumors and tumor margins, demonstrate the potential of NIR photothermal therapy as a viable localized treatment approach for primary and early stage tumors, and prevents NP uptake by the reticuloendothelial system.

Technical and practical considerations for device selection in locoregional ablative therapy

Percutaneous ablation therapy is an essential component of contemporary interventional oncologic therapy of primary and secondary malignancies. The growing armamentarium of available ablation technologies calls for thorough understanding of the different ablation modalities to optimize device selection in individual clinical settings. The goal of the current article is to provide direction on ablative device selection by reviewing device mechanisms of action, advantages and disadvantages, and practical considerations in real-life case scenarios.

Complications of image-guided thermal ablation of liver and kidney neoplasms

Image-guided thermal ablation is a widely accepted tool in the treatment of a variety of solid organ neoplasms. Among the different techniques of ablation, radiofrequency ablation, cryoablation, and microwave ablation have been most commonly used and investigated in the treatment of liver and kidney neoplasms. This article will review complications following thermal ablation of tumors in the liver and kidney, and discuss the risks and clinical presentation of each complication as well as how to treat and potentially avoid complications.