Radiofrequency tumor ablation: principles and techniques

Thermal Ablation versus SBRT in liver tumours: pros and cons

Non-surgical locally ablative treatments for primary liver cancer and liver metastases represent an effective therapeutic choice when surgery cannot be performed or is not indicated. Thermal ablative employing electric currents or electromagnetic fields have historically played an important role in this setting. Radiotherapy, in the last decades, due to a series of important technological development, has become an attractive option for the treatment of liver tumours, especially with the introduction of Stereotactic Body Radiotherapy. Published literature so far evidenced both for radiotherapy and thermal ablative techniques a benefit in terms of local control and other oncological outcomes; however, no direct prospective comparison between the two techniques have been published so far. The aim of this review is to summarize the technical and clinical implications of these treatment modalities and to identify criteria to allocate patients to one or another option in consideration of the expected efficacy. The main features and critical aspects of both thermoablative techniques and external beam radiation will also be covered in the present paper.

Radiofrequency Thermal Ablation of Benign Thyroid Nodules: The Correlation Between Ultrasound Nodule Characteristics and Results

Background. The aim of this observational study was to investigate for which nodules a better response to radiofrequency thermoablation (RFA) for nonfunctioning benign thyroid nodules is likely. Methods. Aesthetic score, compressive score, and volume of 32 benign nodules from 32 patients were registered during follow-up at baseline, 1, 3, 6, and 12 months. Results. A volume reduction rate (VRR) of 72.56% at 12 months after the procedure (P = .009) was registered. A significant (P < .001) improvement in the compressive and aesthetic scores was observed. Nodules with a baseline volume <20 mL had VRRs at 3 and 6 months that were significantly greater than those with volume >20 mL (P = .037). Conclusions. RFA was shown to be a safe and effective procedure for the management of benign thyroid nodules and that there is a correlation between the initial size of the nodule and the response to treatment.

Successful treatment of a huge hepatic carcinoma with right portal vein thrombosis: A case report

INTRODUCTION

Unlike the traditional associating liver partition and portal vein ligation for staged hepatectomy, it is still controversial whether patients with portal vein thrombosis can receive benefits from liver partition.

PATIENT CONCERNS

Right upper abdominal distension for 2 months.

DIAGNOSIS

Hepatocellular carcinoma with portal vein invasion INTERVENTION:: Radiofrequency-assisted liver partition with portal vein ligation (RALPP) OUTCOMES:: Disease-free survival: 3 months, overall survival: 7 months CONCLUSION:: Our results advocate this variation of RALPP for use in patients with huge HCC with portal vein invasion, without enough future liver remnant. Patients can receive benefits from the operation, including a shorter operation time, better recovery, and lower overall costs of the 2-stage procedure.

Conformal coverage of liver tumors by the thermal coagulation zone in 2450-MHz microwave ablation

Purpose: To optimize treatment schemes using 2450-MHz microwave ablation (MWA), a novel conformal coverage method based on bipolar-angle mapping is proposed that determines whether a liver tumor is completely encompassed by thermal coagulation zones. Materials and methods: Firstly, three-dimensional (3-D) triangular mesh data of liver tumors were reconstructed from clinical computed tomography (CT) slices using the Marching cubes (MC) algorithm. Secondly, characterization models of thermal coagulation zones were established based on finite element simulation results of 40, 45, 50, 55, and 60 W ablations. Finally, coagulation zone models and tumor surface data were mapped and fused on a two-dimensional (2-D) plane to achieve conformal coverage of liver tumors by comparing the corresponding polar radii. Results: Optimal parameters for ablation treatment of liver tumors were efficiently obtained with the proposed conformal coverage method. Fifteen liver tumors were obtained with maximal diameters of 12.329-78.612 mm (mean ± standard deviation, 39.094 ± 19.447 mm). The insertion positions and orientations of the MWA antenna were determined based on 3-D reconstruction results of these tumors. The ablation patterns and durations of tumors were planned according to the minimum mean standard deviations between the ablative margin and tumor surface. Conclusion: The proposed method can be applied to computer-assisted MWA treatment planning of liver tumors, and is expected to guide clinical procedures in future.

A Novel Method to Increase Tumor Ablation Zones With RFA by Injecting the Cationic Polymer Solution to Tissues: In Vivo and Computational Studies

OBJECTIVE

This study aims to examine, for the first time, the introduction of cationic polymer solutions to improve radiofrequency ablation (RFA) in terms of a potentially enlarged ablation zone.

METHODS

By using in vivo and computational RFA studies, two cationic polymers, Chitooligosaccharides (COS) and carboxymethyl chitosan (CMC), diluted in deionized water, were injected into tissues separately surrounding the RF bipolar electrode prior to power application. A total of 9 rabbits were used to 1) measure the increase in electrical conductivity of tissues injected with the cationic polymer solutions, and 2) explore the enhancement of the ablation performance in RFA trials. A computer model of RFA comprising a model of the solution diffusion with an RF thermal ablation model was also built, validated by the in vivo experiment, to quantitatively study the effect of cationic polymer solutions on ablation performances.

RESULTS

Compared to the control group, the electrical conductivity of rabbit liver tissues was increased by 42.20% (0.282 ± 0.006 vs. 0.401 ± 0.048 S/m, P = 0.001) and 43.97% (0.282 ± 0.006 vs. 0.406 ± 0.042 S/m, P = 0.001) by injecting the COS and CMC solution at the concentration of 100 mg/mL into the tissues, denoted COS_DW100 and CMC_DW100, respectively. Consequently, the in vivo experiments show that the ablation zone was enlarged by 95% (47.6 ± 6.3 vs. 92.6 ± 11.5 mm², P < 0.001) and 87% (47.6± 6.3 vs. 88.8 ± 9.6 mm², P < 0.001) by COS_DW100 and CMC_DW100, respectively. The computer simulation shows that the ablation zone was enlarged by 71% (51.9 vs. 88.7 mm²) and 63% (51.9 vs. 84.7 mm²) by COS_DW100 and CMC_DW100, respectively.

CONCLUSION

The injection of the cationic solution can greatly improve the performance of RFA treatment in terms of enlarging the ablation zone, which is due to the increase in the electrical conductivity of liver tissues surrounding the RF electrode.

SIGNIFICANCE

This study contributes to the improvement of RFA in the treatment of large tumors.

Large placental chorioangioma: a potential effective in-utero treatment modality for radio frequency ablation

Background

Placenta chorioangiomas are common benign placental tumours. While microscopic chorioangiomas are frequent, macroscopic chorioangiomas of more than 5 cm are rare and often associated with fetal complications such as high output cardiac failure, fetal anaemia and stillbirth. Close monitoring and in-utero treatment are sometimes necessary to prevent adverse pregnancy outcome.

Case presentation

We present two cases of large placenta chorioangiomas with one case requiring surgical therapy with radiofrequency ablation (RFA) of tumour vessels, which resulted in a successful outcome of a live birth at term.

Conclusion

We conclude that RFA is an effective alternative treatment modality to fetoscopic laser therapy in utero for cases at risk of fetal cardiac failure and intrauterine demise in the presence of large chorioangiomas.

Percutaneous thermal ablation of primary and secondary lung tumors: Comparison between microwave and radiofrequency ablation

PURPOSE

The purpose of this study was to retrospectively compare microwave (MWA) and radiofrequency (RFA) ablation in the percutaneous treatment of primary and secondary lung tumors.

MATERIAL AND METHODS

A total of 115 patients with a total of 160 lung tumors (primary, n=41; secondary, n=119) were retrospectively included. There were 56 men and 59 women with a mean age of 67.8±12.7 (SD) years (range: 42-89 years) who underwent either MWA (61 patients; 79 tumors) or RFA (54 patients; 81 tumors). The primary study endpoints were local recurrence during follow-up and the incidence of complications during and following thermal ablation. The MWA and RFA groups were compared in terms of treatment efficacy and complication rates.

RESULTS

Demographics were similar in the two groups. Mean tumor diameter was smaller in RFA group (13.1±5.1 [SD] mm; range: 4-27mm) than in MWA group (17.1±8.3 [SD] mm; range: 5-36mm) (P<0.001). Ablation volumes at one month were 24.1±21.7 (SD) cm³ (range: 2-97.8 cm³) in RFA group and 30.2±35.9 (SD) cm³ (range: 1.9-243.8 cm³) in MWA group (P=0.195). During a mean overall follow-up duration of 488±407 (SD) days (range: 30-1508 days), 9/160 tumors (5.6%) developed local recurrence: six (6/79; 7.6%) in the RFA group and three (3/81; 3.7%) in the MWA group (P=0.32). Pneumothoraces were more frequent in the RFA group (32/79; 40.5%) than in the MWA group (20/81; 24.7%) (P=0.049). The mean length of hospital stay was 4.5±3.7 (SD) days (range: 1-25 days) in the RFA group and 4.7±4.6 (SD) days (range: 2-25 days) in the MWA group (P=0.76).

CONCLUSIONS

MWA favorably compares with RFA and can be considered as an effective and safe thermal ablation technique for lung tumors, especially in situations where RFA has limited efficacy.

The Role of a Curved Electrode with Controllable Direction in the Radiofrequency Ablation of Liver Tumors Behind Large Vessels

PURPOSE

To investigate the role of a novel curved radiofrequency ablation (RFA) electrode with controllable direction in the ablation of tumors behind large hepatic vessels in ex vivo bovine and in vivo canine liver experiments.

MATERIALS AND METHODS

Approval from the institutional animal care and use committee was obtained. In ex vivo experiments, conventional multi-tines expandable electrodes, conventional monopolar straight electrodes and novel curved electrodes were used in the ablation of the bovine liver (n = 90). The ablated area, parallel axis, vertical axis and shape of different electrodes were compared. Then, 24 beagle dogs (10 months old, female) were used for in vivo experiments. Visual tumor targets deeply located in the portal vein were established, and ultrasound-guided liver ablation was performed with different electrodes. The ablation range, target coverage rate, percentage of normal tissue injury and damage to adjacent vessels were evaluated. The Kruskal-Wallis test and the Chi-squared test were used for statistical analysis.

RESULTS

For the ex vivo study with a 3-cm electrode, the ablation area of the multi-tines expandable electrode group (7.14 ± 0.16 cm2) was significantly larger than that of the novel curved electrode group (5.01 ± 0.30 cm2, P < 0.001) and the monopolar straight electrode group (5.43 ± 0.15 cm2, P < 0.001). The results obtained with the 4-cm electrode in the three groups were in accordance with those of the 3-cm electrode. In vivo, the normal tissue damage area of the novel curved electrode group was smaller than that of the multi-tines expandable electrode group (1.10 ± 0.18 cm2 vs. 4.00 ± 0.18 cm2, P < 0.001). The target coverage rate of the novel curved electrode group was better than that of the monopolar straight electrode group (100% vs. 80.86 ± 1.68%, P < 0.001). The hematoxylin and eosin (H&E) and TUNEL staining results showed that the ablation necrosis area was adjacent to large vessels, but the vascular wall was not significantly damaged in the novel curved electrode group.

CONCLUSION

Our preliminary results showed that the novel curved RFA electrode with controllable direction could achieve accurate ablation for tumors behind large hepatic vessels, with a better target coverage rate and less damage to normal tissue, than conventional multi-tines expandable electrodes and monopolar straight electrodes.

Microwave Ablation of Primary Malignant Pelvic Bone Tumors

Background: En bloc tumor resection followed by reconstruction is a widely used surgical treatment for malignant pelvic bone tumors. High rates of complications and mechanical instability often contribute to poor postoperative results. We attempted en bloc microwave ablation (MWA) in situ to improve the outcome.

Methods: From May 1995 to December 2015, 104 patients with primary pelvic malignancy received radical MWA in our department. After careful dissection of the tumor-bearing bone from surrounding normal tissues with safe margins, a microwave antenna array was inserted into the tumor mass to emit electromagnetic energy, inducing tumor cellular death via thermocoagulation. The loose, devitalized tumor tissues were removed by cutting or curettage, leaving a defective bone scaffold. Re-strengthening by autograft or allograft was needed in most patients.

Results: The over 3 years survival rate was 51.5% for high-grade malignancies (among them, 26.9% were osteosarcoma) and 94.8% for low-grade malignancies (chondrosarcoma). In most of the living patients, cosmetic and useful limbs were preserved. The mean functional score (Musculoskeletal Tumor Society) was 27 or 90% (range: 25–30, 75–100%). Among the 56 patients who belonged to the excellent function group, 11 were followed up for more than 10 years. The local recurrence rate was 8.6%. Among the 9 patients with recurrence, 5 died from disease, 2 were treated by hemipelvic amputation, and 2 underwent revision surgery with MWA and gained local control. The deep infection rate was 5.6%. All six patients with infection were healed by irrigation, debridement, and systemic antibiotic administration.

Conclusion: Local, microwave-induced hyperthermia for treating malignant pelvic bone tumors is an effective alternative method. The oncological and functional results are encouraging. The use of MWA should be continued to evaluate and improve this new therapeutic system.

Interstitial magnetic thermotherapy dosimetry based on shear wave magnetomotive optical coherence elastography

While magnetic thermoseeds are often utilized in interstitial magnetic thermotherapy (iMT) to enable localized tumor ablation, we propose to extend their use as the perturbative source in magnetomotive optical coherence elastography (MM-OCE) so that the heat-induced elasticity alterations can be 'theranostically' probed. MM-OCE measurements were found to agree with indentation results. Tissue stiffening was visualized on iMT-treated porcine liver and canine soft tissue sarcoma specimens, where histology confirmed thermal damages. Additionally, the elasticity was found to increase exponentially and linearly with the conventional thermal dosage metrics and the deposited thermal energy, respectively. Collectively, a physiologically-meaningful, MM-OCE-based iMT dosimetry is feasible.

Magnetically targeted nanoparticles for imaging-guided photothermal therapy of cancer

Over the past several decades, nanocarriers have constituted a vital research area for accurate tumor therapy. Herein, magnetically targeted nanoparticles (IRFes) for photothermal therapy were generated by integrating IR780, a molecule with strong emission and absorption in the NIR spectrum and the ability to produce heat after laser irradiation, with Fe₃O₄ nanoparticles (NPs). These IRFes were guided to the tumor site by the application of an external magnetic field. In particular, the strong NIR absorption of IR780 was used for NIRF imaging, and we also demonstrated effective magnetic targeting for the photothermal ablation of tumors. In vitro cell viability and in vivo antitumor experiments showed that these IRFes can ablate 4T1 cells or transplanted 4T1 cell tumors when exposed to 808 nm laser irradiation and a magnetic field. In vivo experiments showed that IRFes only act on tumors, do not damage other organs and can be used to image tumors. These results demonstrate the enormous potential of local photothermal therapy for cancer under the guidance of external magnetic fields and reveal the prospect for the use of multifunctional nanoparticles in tumor therapy.

Magnetically targeted nanoparticles (IRFes) for photothermal therapy were generated by integrating IR780, a molecule with strong emission and absorption in the NIR spectrum and the ability to produce heat after laser irradiation, with Fe₃O₄ nanoparticles.

Thermal ablation of pancreatic cancer: A systematic literature review of clinical practice and pre-clinical studies

PURPOSE

Pancreatic cancer is a challenging malignancy with low treatment option and poor life expectancy. Thermal ablation techniques were proposed as alternative treatment options, especially in advanced stages and for unfit-for-surgery patients. This systematic review describes the thermal ablative techniques -i.e., Laser (LA), Radiofrequency (RFA), Microwave (MWA) Ablation, High-Intensity Focused Ultrasound (HIFU) and cryoablation- available for pancreatic cancer treatment. Additionally, an analysis of the efficacy, complication rate and overall survival for each technique is conducted.

MATERIAL AND METHODS

This review collects the ex vivo, preclinical and clinical studies presenting the use of thermal techniques in the pancreatic cancer treatment, searched up to March 2018 in PubMed and Medline. Abstracts, letters-to-the-editor, expert opinions, reviews and non-English language manuscripts were excluded.

RESULTS

Sixty-five papers were included. For the ex vivo and preclinical studies, there are: 12 records for LA, 8 for RFA, 0 for MWA, 6 for HIFU, 1 for cryoablation and 3 for hybrid techniques. For clinical studies, 1 paper for LA, 14 for RFA, 1 for MWA, 17 for HIFU, 1 for cryoablation and 1 for hybrid techniques.

CONCLUSIONS

Important technological advances are presented in ex vivo and preclinical studies, as the real-time thermometry, nanotechnology and hybrid techniques to enhance the thermal outcome. Conversely, a lack of standardization in the clinical employment of the procedures emerged, leading to contrasting results on the safety and feasibility of some analyzed techniques. Uniform conclusions on the safety and feasibility of these techniques for pancreatic cancer will require further structured investigation.

Percutaneous Laser Ablation of Unifocal Papillary Thyroid Microcarcinoma: Utility of Conventional Ultrasound and Contrast-Enhanced Ultrasound in Assessing Local Therapeutic Response

PURPOSE

To investigate the use of conventional ultrasound and contrast-enhanced ultrasound (CEUS) in assessing local therapeutic response of percutaneous laser ablation (PLA) for papillary thyroid microcarcinoma (PTMC).

METHODS

Sixty-four patients with 64 PTMCs who were referred to our hospital from November 2013 to July 2016 were treated with PLA. The extent of ablation was assessed by CEUS at 10-20 min and 7 days after PLA. The size and volume of the ablation zone were evaluated on conventional ultrasound at 1 h, 1, 3, 6 and 12 months, and every half-year thereafter, and recurrences were also recorded. Ultrasound-guided fine needle aspiration biopsy (FNAB) of the ablated area was performed at 1, 6 and 12 months after PLA.

RESULTS

Two incomplete ablations were detected by CEUS, and a second ablation was performed. The mean largest diameter and volume of the ablated area on CEUS at 10-20 min and 7 days after PLA were significantly larger than those of pre-treatment on conventional ultrasound (p < 0.05, for both). At the last follow-up, the mean largest diameter was reduced from 4.6 ± 1.5 to 0.6 ± 1.3 mm (p < 0.0.5), and the average volume was 41.0 ± 40.4 mm³, which decreased to 1.8 ± 6.7 mm³ (p < 0.0.5). A cervical metastatic lymph node was detected on ultrasound and confirmed by ultrasound-guided FNAB at 30 months after PLA.

CONCLUSIONS

CEUS could play a crucial role in assessing the completeness of PLA for treating PTMC, and conventional ultrasound can not only guide the FNAB process but also is important in the follow-up of PTMC after PLA.

Moxibustion-Simulating Bipolar Radiofrequency Suppresses Weight Gain and Induces Adipose Tissue Browning via Activation of UCP1 and FGF21 in a Mouse Model of Diet-Induced Obesity

Background

Obesity is a pathological condition associated with various diseases including diabetes, stroke, arthritis, infertility, and heart disease. Moxibustion is widely used to prevent and manage obesity in traditional Asian medicine. We tested our hypothesis that moxibustion-simulating bipolar radiofrequency (M-RF) can suppress total body and white adipose tissue (WAT) weight gain via induction of WAT browning in a mouse model of diet-induced obesity (DIO).

Methods

We designed an M-RF device that could accurately adjust the depth and temperature at which heat stimulation was administered into the abdomen of DIO mice. High-fat-fed male C57BL/6 mice were treated with the M-RF device every two or three days for three weeks. We then harvested WAT and serum from the mice and measured total body and WAT weight, size of adipocytes, mitochondrial contents, features of the dead adipocyte environment, and levels of uncoupling protein 1 (UCP1) and fibroblast growth factor 21 (FGF21).

Results

Heat stimulation by M-RF in DIO mice resulted in precise temperature adjustment in the mice abdomen, with variance less than 1°C. Additionally, M-RF stimulation inhibited body and WAT weight gain, resulting in increased formation of beige adipocytes, increased mitochondrial content, and decreased formation of dead adipocytes in WAT. Moreover, treatment of M-RF induced expression of UCP1 and FGF21 in serum and/or epididymal WATs in DIO mice.

Conclusion

Heat stimulation by M-RF treatment induced upregulation of UCP1 and FGF21 expression in serum and/or WATs, which was correlated with reduced total body and WAT weight gain in DIO mice.

Dissociated effect and Chemosensitive enhancement of tumor spheroids influenced by an electric field in a microdevice

The use of electric field for cancer therapy has been proposed for a novel non-invasive cancer therapeutic approach that provides better quality of life for patients. However, argument of the efficacy hampers the therapeutic development for various cancer diseases. More scientific evidences are necessary to be addressed by basic research. The current in vitro cell culture study reports the responses of tumor spheroids after the application of an alternating electric field. Human hepatocarchinoma cells suspended in soft hydrogel were cultured in a cell culture device embedded with stimulating electrodes. Tumor spheroids gradually formed and alternating electric field was then applied during the culture course. Investigation of cell viability and cell cycle were conducted to optimize the treatment conditions. The results showed that the electric potential of 1.0 Vpp and frequency of 130 kHz was the minimal effective conditions for inhibiting tumor spheroids. Importantly, dissociation of tumor spheroids was observed after the treatment. The effectiveness of chemotherapeutic agents was shown to be enhanced while the electric filed was simultaneously applied to the tumor spheroids. These results provided solid foundation for developing the effective therapeutic strategies.

Serum miR-130b level, an ideal marker for monitoring the recurrence and prognosis of primary hepatocellular carcinoma after radiofrequency ablation treatment

OBJECTIVE

This study was aimed to explore the potential roles of miR-130b for the efficacy of radiofrequency ablation (RFA) in patients with primary hepatocellular carcinoma (PHC).

METHODS

The serum sample of 110 PHC patients, which underwent RFA treatment, was collected on 1d pre-operation (Pre 1), 7d (POD 7) and 14d post-operation (POD 14). qRT-PCR was used to detect miR-130b expression. The relationship between miR-130b expression and clinicopathological features, postoperative recurrence and survival rate were analyzed.

RESULTS

The liver function of PHC patients was improved after RFA treatment. The level of alpha fetoprotein (AFP) was gradually reduced on POD 7 and POD 14 (all P <  0.05). Before RFA, the expression of miR-130b in PHC patients was upregulated, while the expression of miR-130b decreased significantly with time after RFA treatment. And high expression of miR-130b was closely related to cirrhosis (P =  0.027) and tumor differentiation degree (P <  0.01). Serum miR-130b levels were significantly higher in patients with recurrence than in patients without recurrence (P <  0.05). Patients were divided into two groups according to miR-130b expression level (median ΔCt), compared with low ΔCt group, the incidence of recurrence in high ΔCt group was significantly higher after RFA (P =  0.020). Kaplan-Meier survival analysis showed that the survival rate of high ΔCt group was significantly shorter than that of low ΔCt group (P <  0.001).

CONCLUSION

Our study provided evidence that serum miR-130b level may be used as an ideal marker for monitoring the recurrence and prognosis of PHC after RFA treatment.

Recent Advances in the Image-Guided Tumor Ablation of Liver Malignancies: Radiofrequency Ablation with Multiple Electrodes, Real-Time Multimodality Fusion Imaging, and New Energy Sources

Radiofrequency ablation (RFA) has emerged as an effective loco-regional treatment modality for malignant hepatic tumors. Indeed, studies have demonstrated that RFA of early stage hepatocellular carcinomas can provide comparable overall survival to surgical resection. However, the incidence of local tumor progression (LTP) after RFA is significantly higher than that of surgical resection. Thus, to overcome this limitation, multiple electrode radiofrequency (RF) systems that use a multi-channel RF generator have been developed, and they demonstrate better efficiency in creating larger ablation zones than that using the conventional RFA with a single electrode. Furthermore, RFA with multiple electrodes can allow the “no-touch” ablation technique which may also help to reduce LTP. Another technique that would be helpful in this regard is multi-modality-ultrasound fusion imaging, which helps to not only more accurately determine the target lesion by enabling the RFA of small, poorly visible or invisible tumors, but also improve the monitoring of procedures and determine the appropriateness of the ablation margin. In addition, new energy sources, including microwave and cryoablation, have been introduced in imaging-guided tumor ablation. In this review, these recently introduced ablation techniques and the results of the most current animal and clinical studies are discussed.

Time and temperature dependence of radiofrequency ablation in the human placenta

OBJECTIVE

The objective of the study is to compare radiofrequency (RF) effects on fresh placentae with varying levels of sustained time (Ts) and degrees of target temperature (°t).

METHOD

A total of 108 pieces of fresh placentae were coagulated with a 2-cm RF needle at 60 W in an organ bath. The vertical and horizontal diameters (Vd, Hd) of tissue coagulation visualized by ultrasound were measured. The impacts of 12 different Ts-°t combinations on the ablation size ascertained on pathological examination (Vd_p , Hd_p ) were compared using 2-way ANOVA. The agreement between sonographic and pathological findings was assessed using Bland-Altman analysis.

RESULTS

Considerable changes in the Vd_p and Hd_p were associated with increasing the Ts and °t. The impact of RF on tissue coagulation was greatest when the °t was set at 100°C, with further destruction as the Ts progressed to 7 minutes of exposure. The ablation size estimated by ultrasound exhibited an overestimation by an average of 5.65% and 21.02% for Vd and Hd, respectively.

CONCLUSION

A prolonged Ts at a higher °t contributes to progressive placental tissue destruction by RF, with maximum destruction at 100°C for 7 minutes in an ex vivo nonperfused placenta. Tissue injury that is apparent on ultrasound may extend beyond pathological damage.

Integrated catheter for simultaneous radio frequency ablation and optoacoustic monitoring of lesion progression

Radio frequency (RF) catheter ablation is commonly used to eliminate dysfunctional cardiac tissue by heating via an alternating current. Clinical outcomes are highly dependent on careful anatomical guidance, electrophysiological mapping, and careful RF power titration during the procedure. Yet, current treatments rely mainly on the expertise of the surgeon to assess lesion formation, causing large variabilities in the success rate. We present an integrated catheter design suitable for simultaneous RF ablation and real-time optoacoustic monitoring of the forming lesion. The catheter design utilizes copper-coated multimode light guides capable of delivering both ablation current and near-infrared pulsed-laser illumination to the target tissue. The generated optoacoustic responses were used to visualize the ablation lesion formation in an ex-vivo bovine heart specimen in 3D. The presented catheter design enables the monitoring of ablation lesions with high spatiotemporal resolution while the overall therapy-monitoring approach remains compatible with commercially available catheter designs.

Multifunctional fluorescent iron quantum clusters for non-invasive radiofrequency ablationof cancer cells

This work reports the potential of iron quantum clusters (FeQCs) as a hyperthermia agent for cancer, by testing its in-vitro response to shortwave (MHz range), radiofrequency (RF) waves non-invasively. Stable, fluorescent FeQCs of size ∼1 nm prepared by facile aqueous chemistry from endogenous protein haemoglobin were found to give a high thermal response, with a ΔT ∼50 °C at concentrationsas low as165 μg/mL. The as-prepared nanoclusters purified by lyophilization as well as dialysis showed a concentration, power and time-dependent RF response, with the lyophilized FeQCs exhibiting pronounced heating effects. FeQCs were found to be cytocompatible to NIH-3T3 fibroblast and 4T1 cancer cells treated at concentrations upto 1000 μg/mL for 24 h. Upon incubation with FeQCs and exposure to RF waves, significant cancer cell death was observed which proves its therapeutic ability. The fluorescent ability of the clusters could additionally be utilized for imaging cancer cells upon excitation at ∼450 nm. Further, to demonstrate the feasibility of imparting additional functionality such as drug/biomolecule/dye loading to FeQCs, they were self assembled with cationic polymers to form nanoparticles. Self assembly did not alter the RF heating potential of FeQCs and additionally enhanced its fluorescence. The multifunctional fluorescent FeQCs therefore show good promise as a novel therapeutic agent for RF hyperthermia and drug loading.

RFA Guardian: Comprehensive Simulation of Radiofrequency Ablation Treatment of Liver Tumors

The RFA Guardian is a comprehensive application for high-performance patient-specific simulation of radiofrequency ablation of liver tumors. We address a wide range of usage scenarios. These include pre-interventional planning, sampling of the parameter space for uncertainty estimation, treatment evaluation and, in the worst case, failure analysis. The RFA Guardian is the first of its kind that exhibits sufficient performance for simulating treatment outcomes during the intervention. We achieve this by combining a large number of high-performance image processing, biomechanical simulation and visualization techniques into a generalized technical workflow. Further, we wrap the feature set into a single, integrated application, which exploits all available resources of standard consumer hardware, including massively parallel computing on graphics processing units. This allows us to predict or reproduce treatment outcomes on a single personal computer with high computational performance and high accuracy. The resulting low demand for infrastructure enables easy and cost-efficient integration into the clinical routine. We present a number of evaluation cases from the clinical practice where users performed the whole technical workflow from patient-specific modeling to final validation and highlight the opportunities arising from our fast, accurate prediction techniques.

Design of a Novel Electrode of Radiofrequency Ablation for Large Tumors: A Finite Element Study

The aim of the study was to design a novel radiofrequency (RF) electrode for larger and rounder ablation volumes and its ability to achieve the complete ablation of liver tumors larger than 3 cm in diameter using finite element method. A new RF expandable electrode comprising three parts (i.e., insulated shaft, changing shaft, and hooks) was designed. Two modes of this new electrode, such as monopolar expandable electrode (MEE) and hybrid expandable electrode (HEE), and a commercial expandable electrode (CEE) were investigated using liver tissue with (scenario I) and without (scenario II) a liver tumor. A temperature-controlled radiofrequency ablation (RFA) protocol with a target temperature of 95 °C and an ablation time of 15 min was used in the study. Both the volume and shape of the ablation zone were examined for all RF electrodes in scenario I. Then, the RF electrode with the best performance in scenario I and CEE were used to ablate a large liver tumor with the diameter of 3.5 cm (scenario II) to evaluate the effectiveness of complete tumor ablation of the designed RF electrode. In scenario I, the ablation volumes of CEE, HEE, and MEE were 12.11 cm3, 33.29 cm3, and 48.75 cm3, respectively. The values of sphericity index (SI) of CEE, HEE, and MEE were 0.457, 0.957, and 0.976, respectively. The best performance was achieved by using MEE. In scenario II, the ablation volumes of MEE and CEE were 71.59 cm3 and 19.53 cm3, respectively. Also, a rounder ablation volume was achieved by using MEE compared to CEE (SI: 0.978 versus 0.596). The study concluded that: (1) compared with CEE, both MEE and HEE get larger and rounder ablation volumes due to the larger electrode–tissue interface and rounder shape of hook deployment; (2) MEE has the best performance in getting a larger and rounder ablation volume; and (3) computer simulation result shows that MEE is also able to ablate a large liver tumor (i.e., 3.5 cm in diameter) completely, which has at least 0.785 cm safety margin.

Model-based optimal planning of hepatic radiofrequency ablation

This article presents a model-based pre-treatment optimal planning framework for hepatic tumour radiofrequency (RF) ablation. Conventional hepatic radiofrequency (RF) ablation methods rely on pre-specified input voltage and treatment length based on the tumour size. Using these experimentally obtained pre-specified treatment parameters in RF ablation is not optimal to achieve the expected level of cell death and usually results in more healthy tissue damage than desired. In this study we present a pre-treatment planning framework that provides tools to control the levels of both the healthy tissue preservation and tumour cell death. Over the geometry of tumour and surrounding tissue, we formulate the RF ablation planning as a constrained optimization problem. With specific constraints over the temperature profile (TP) in pre-determined areas of the target geometry, we consider two different cost functions based on the history of the TP and Arrhenius index (AI) of the target location, respectively. We optimally compute the input voltage variation to minimize the damage to the healthy tissue while ensuring a complete cell death in the tumour and immediate area covering the tumour. As an example, we use a simulation of a 1D symmetric target geometry mimicking the application of single electrode RF probe. Results demonstrate that compared to the conventional methods both cost functions improve the healthy tissue preservation.

Theranostic Iron Oxide/Gold Ion Nanoprobes for MR Imaging and Noninvasive RF Hyperthermia

This work focuses on the development of a nanoparticulate system that can be used for magnetic resonance (MR) imaging and E-field noninvasive radiofrequency (RF) hyperthermia. For this purpose, an amine-functional gold ion complex (GIC), [Au(III)(diethylenetriamine)Cl]Cl₂, which generates heat upon RF exposure, was conjugated to carboxyl-functional poly(acrylic acid)-capped iron-oxide nanoparticles (IO-PAA NPs) to form IO-GIC NPs of size ∼100 nm. The multimodal superparamagnetic IO-GIC NPs produced T2-contrast on MR imaging and unlike IO-PAA NPs generated heat on RF exposure. The RF heating response of IO-GIC NPs was found to be dependent on the RF power, exposure period, and particle concentration. IO-GIC NPs at a concentration of 2.5 mg/mL showed a high heating response (δT) of ∼40 °C when exposed to 100 W RF power for 1 min. In vitro cytotoxicity measurements on NIH-3T3 fibroblast cells and 4T1 cancer cells showed that IO-GIC NPs are cytocompatible at high NP concentrations for up to 72 h. Upon in vitro RF exposure (100 W, 1 min), a high thermal response leads to cell death of 4T1 cancer cells incubated with IO-GIC NPs (1 mg/mL). Hematoxylin and eosin imaging of rat liver tissues injected with 100 μL of 2.5 mg/mL IO-GIC NPs and exposed to low RF power of 20 W for 10 min showed significant loss of tissue morphology at the site of injection, as against RF-exposed or nanoparticle-injected controls. In vivo MR imaging and noninvasive RF exposure of 4T1-tumor-bearing mice after IO-GIC NP administration showed T2 contrast enhancement and a localized generation of high temperatures in tumors, leading to tumor tissue damage. Furthermore, the administration of IO-GIC NPs followed by RF exposure showed no adverse acute toxicity effects in vivo. Thus, IO-GIC NPs show good promise as a theranostic agent for magnetic resonance imaging and noninvasive RF hyperthermia for cancer.

Adaptive ultrasound temperature imaging for monitoring radiofrequency ablation

Radiofrequency ablation (RFA) has been widely used as an alternative treatment modality for liver tumors. Monitoring the temperature distribution in the tissue during RFA is required to assess the thermal dosage. Ultrasound temperature imaging based on the detection of echo time shifts has received the most attention in the past decade. The coefficient k, connecting the temperature change and the echo time shift, is a medium-dependent parameter used to describe the confounding effects of changes in the speed of sound and thermal expansion as temperature increases. The current algorithm of temperature estimate based on echo time shift detection typically uses a constant k, resulting in estimation errors when ablation temperatures are higher than 50°C. This study proposes an adaptive-k algorithm that enables the automatic adjustment of the coefficient k during ultrasound temperature monitoring of RFA. To verify the proposed algorithm, RFA experiments on in vitro porcine liver samples (total n = 15) were performed using ablation powers of 10, 15, and 20 W. During RFA, a clinical ultrasound system equipped with a 7.5-MHz linear transducer was used to collect backscattered signals for ultrasound temperature imaging using the constant- and adaptive-k algorithms. Concurrently, an infrared imaging system and thermocouples were used to measure surface temperature distribution of the sample and internal ablation temperatures for comparisons with ultrasound estimates. Experimental results demonstrated that the proposed adaptive-k method improved the performance in visualizing the temperature distribution. In particular, the estimation errors were also reduced even when the temperature of the tissue is higher than 50°C. The proposed adaptive-k ultrasound temperature imaging strategy has potential to serve as a thermal dosage evaluation tool for monitoring high-temperature RFA.

Adaptive ultrasound temperature imaging for monitoring radiofrequency ablation

Radiofrequency ablation (RFA) has been widely used as an alternative treatment modality for liver tumors. Monitoring the temperature distribution in the tissue during RFA is required to assess the thermal dosage. Ultrasound temperature imaging based on the detection of echo time shifts has received the most attention in the past decade. The coefficient k, connecting the temperature change and the echo time shift, is a medium-dependent parameter used to describe the confounding effects of changes in the speed of sound and thermal expansion as temperature increases. The current algorithm of temperature estimate based on echo time shift detection typically uses a constant k, resulting in estimation errors when ablation temperatures are higher than 50°C. This study proposes an adaptive-k algorithm that enables the automatic adjustment of the coefficient k during ultrasound temperature monitoring of RFA. To verify the proposed algorithm, RFA experiments on in vitro porcine liver samples (total n = 15) were performed using ablation powers of 10, 15, and 20 W. During RFA, a clinical ultrasound system equipped with a 7.5-MHz linear transducer was used to collect backscattered signals for ultrasound temperature imaging using the constant- and adaptive-k algorithms. Concurrently, an infrared imaging system and thermocouples were used to measure surface temperature distribution of the sample and internal ablation temperatures for comparisons with ultrasound estimates. Experimental results demonstrated that the proposed adaptive-k method improved the performance in visualizing the temperature distribution. In particular, the estimation errors were also reduced even when the temperature of the tissue is higher than 50°C. The proposed adaptive-k ultrasound temperature imaging strategy has potential to serve as a thermal dosage evaluation tool for monitoring high-temperature RFA.

Ablation zone visualization enhancement by periodic contrast-enhancement computed tomography during microwave ablation

PURPOSE

Intra-procedural contrast-enhanced computed tomography (CECT) has been proposed to monitor the growth of thermal ablations. The primary challenge with multiple CT acquisitions is reducing radiation dose while maintaining sufficient image quality. The purpose of this study was to evaluate the feasibility of applying local highly constrained backprojection reconstruction (HYPR-LR) on periodic CECT images acquired with low-dose protocols, and to determine whether the ablations visible on CT were commensurate to gross pathology.

METHODS

Low-dose (CTDIvol≤1.49mGy), temporal CECT volumes were acquired during microwave ablation on normal porcine liver. HYPR processing was performed on each volume after image registration. Ablation signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were collected to evaluate the degree of enhancement of image quality and ablation zone visualization. Ablation zones were manually segmented on HYPR and non-HYPR images and compared spatially using Dice's coefficient. The dimensions of ablation zones were also compared to gross pathology by correlation and dimensional differences.

RESULTS

The SNR and CNR of ablation zones were increased after HYPR processing. The manually segmented ablation zone was highly similar to gross pathology with a Dice coefficient of 0.81 ± 0.03, while the low-dose CECT had a smaller Dice coefficient of 0.72 ± 0.05. Both HYPR and low-dose CECT had high correlation to gross pathology (0.99 and 0.94, respectively), but the variance of measurements were lower after HYPR processing compared to unprocessed images. The relative difference in area, length of long axis, and length of short axis for HYPR image were 13.1 ± 5.6%, 9.7 ± 4.2%, and 15.2 ± 2.8%, which were lower than those for low-dose CECT at 37.5 ± 6.0%, 17.7 ± 2.8%, and 28.9 ± 5.4%.

CONCLUSION

HYPR processing applied to periodic CECT images can enhance ablation zone visualization. HYPR processing may potentially enable CECT in real-time ablation monitoring under strict regulation of radiation dose.

A Comparative Study of Ablation Boundary Sharpness After Percutaneous Radiofrequency, Cryo-, Microwave, and Irreversible Electroporation Ablation in Normal Swine Liver and Kidneys

PURPOSE

To compare ablation boundary sharpness after percutaneous radiofrequency ablation (RFA), cryoablation (CA), microwave ablation (MWA) and irreversible electroporation (IRE) ablation in normal swine liver and kidney.

MATERIALS AND METHODS

Percutaneous CT-guided RFA (n = 5), CA (n = 5), MWA (n = 5) and IRE (n = 5) were performed in the liver and kidney of four Yorkshire pigs. Parameters were chosen to produce ablations 2-3 cm in diameter with a single ablation probe. Contrast-enhanced CT imaging was performed 24 h after ablation, and animals were killed. Treated organs were removed and processed for histologic analysis with hematoxylin and eosin, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). Three readers independently analyzed CT, H&E and TUNEL stained images of the ablation boundary to delineate regions of (1) viable cells, (2) complete necrosis or (3) mixture of viable and necrotic cells which was defined as the transition zone (TZ). The width of TZ was compared across the techniques and organs.

RESULTS

Ablations appeared as non-contrast-enhancing regions on CT with sharp transition to enhancing normal tissue. On TUNEL stained slides, the mean width (μm) of the TZ after MWA was 319 ± 157 in liver and 267 ± 95 in kidney, which was significantly lower than RFA (811 ± 477 and 938 ± 429); CA (452 ± 222 and 700 ± 563); and IRE (1319 ± 682 and 1570 ± 962) (all p < 0.01). No significant differences were observed between the organs.

CONCLUSION

Under similar conditions, the width of the TZ at the ablation boundary varies significantly between different ablation techniques.

Performance of radiofrequency ablation used for metastatic spinal tumor: Numerical approach

Surgical treatment of spine metastases follows only local anatomical and biomechanical objectives. Few cases of actual solitary metastases are rather exceptional, while removal of these metastases and the primary tumor may help to eradicate the process. The aim of our subsequent numerical simulations was to find out the temperature distribution and the volume lesion in a spinal tumor. For this purpose, the parametric three-dimensional numerical model was developed. It was shown that by finite element modeling approach not only the temperature distribution but even the resulted cavity may be estimated. The numerical approach was shown as a strong tool in surgery planning.

Minimally invasive local ablative therapies in combination with radioiodine therapy in benign thyroid disease: preparation, feasibility and efficiency - preliminary results

PURPOSE

Initial studies of combinations of radioiodine therapy (RIT) and local ablative procedures for the treatment of thyroid nodules have shown promising results. The goal of this study was to evaluate the effectiveness of RIT combined with radiofrequency ablation (RFA) in patients with goitres and to determine which ablative procedure is the most suitable for a combined therapy.

METHODS

Thirty patients with goitres were divided into two subgroups. A test group of 15 patients received combined therapy (RIT + RFA) and a control group of 15 patients received RIT mono therapy. All patients underwent assessments including ultrasound, laboratory evaluation (T3, T4, TSH, TG, TPOAb, TgAbTRAb) and scintigraphic imaging with Tc-99m-Pertechnetate. The 3-month volume reduction was used to evaluate therapy effectiveness.

RESULTS

Combined therapy (subgroup 1) resulted in a significant (p < 0.05) thyroid volume reduction (22.3 ± 54 ml/32.2 ± 58.2%) with better performance (p > 0.05) than the control group (20.2 ± 32.2 ml/29.6 ± 42.1%). All patients became euthyroid after treatment. No major discomfort or complications occurred. A review of the literature investigating combinations of other local ablative procedures with RIT was performed to determine the most promising combination.

CONCLUSIONS

The present study confirms the positive experiences with the combined therapy of RIT and local ablative procedures shown in the current literature and approves this approach for the treatment of goitres with RFA + RIT. These findings, when confirmed by further studies, should expand the indication of combined therapy as a minimally invasive alternative to surgery.

Finding Optimal Ablation Parameters for Multipolar Radiofrequency Ablation

PURPOSE

Radiofrequency ablation (RFA) for primary liver tumors and liver metastases is restricted by a limited ablation size. Multipolar RFA is a technical advancement of RFA, which is able to achieve larger ablations. The aim of this ex vivo study was to determine optimal ablation parameters for multipolar RFA depending on applicator distance and energy input.

METHODS

RFA was carried out ex vivo in porcine livers with three internally cooled, bipolar applicators in multipolar ablation mode. Three different applicator distances were used and five different energy inputs were examined. Ablation zones were sliced along the cross-sectional area at the largest ablation diameter, orthogonally to the applicators. These slices were digitally measured and analyzed.

RESULTS

Sixty RFA were carried out. A limited growth of ablation area was seen in all test series. This increase was dependent on ablation time, but not on applicator distance. A steady state between energy input and energy loss was not observed. A saturation of the minimum radius of the ablation zone was reached. Differences in ablation radius between the three test series were seen for lowest and highest energy input ( P < .05). No differences were seen for medium amounts of energy ( P > .05).

CONCLUSIONS

The ablation parameters applicator distance and energy input can be chosen in such a way, that minor deviations of the preplanned ablation parameters have no influence on the size of the ablation area.

Chemophototherapy: An Emerging Treatment Option for Solid Tumors

Near infrared (NIR) light penetrates human tissues with limited depth, thereby providing a method to safely deliver non-ionizing radiation to well-defined target tissue volumes. Light-based therapies including photodynamic therapy (PDT) and laser-induced thermal therapy have been validated clinically for curative and palliative treatment of solid tumors. However, these monotherapies can suffer from incomplete tumor killing and have not displaced existing ablative modalities. The combination of phototherapy and chemotherapy (chemophototherapy, CPT), when carefully planned, has been shown to be an effective tumor treatment option preclinically and clinically. Chemotherapy can enhance the efficacy of PDT by targeting surviving cancer cells or by inhibiting regrowth of damaged tumor blood vessels. Alternatively, PDT-mediated vascular permeabilization has been shown to enhance the deposition of nanoparticulate drugs into tumors for enhanced accumulation and efficacy. Integrated nanoparticles have been reported that combine photosensitizers and drugs into a single agent. More recently, light-activated nanoparticles have been developed that release their payload in response to light irradiation to achieve improved drug bioavailability with superior efficacy. CPT can potently eradicate tumors with precise spatial control, and further clinical testing is warranted.

Improving cancer therapies by targeting the physical and chemical hallmarks of the tumor microenvironment

Tumors are highly heterogeneous at the patient, tissue, cellular, and molecular levels. This multi-scale heterogeneity poses significant challenges for effective therapies, which ideally must not only distinguish between tumorous and healthy tissue, but also fully address the wide variety of tumorous sub-clones. Commonly used therapies either leverage a biological phenotype of cancer cells (e.g. high rate of proliferation) or indiscriminately kill all the cells present in a targeted volume. Tumor microenvironment (TME) targeting represents a promising therapeutic direction, because a number of TME hallmarks are conserved across different tumor types, despite the underlying genetic heterogeneity. Historically, TME targeting has largely focused on the cells that support tumor growth (e.g. vascular endothelial cells). However, by viewing the intrinsic physical and chemical alterations in the TME as additional therapeutic opportunities rather than barriers, a new class of TME-inspired treatments has great promise to complement or replace existing therapeutic strategies. In this review we summarize the physical and chemical hallmarks of the TME, and discuss how these tumor characteristics either currently are, or may ultimately be targeted to improve cancer therapies.

GPU-based RFA simulation for minimally invasive cancer treatment of liver tumours

PURPOSE

Radiofrequency ablation (RFA) is one of the most popular and well-standardized minimally invasive cancer treatments (MICT) for liver tumours, employed where surgical resection has been contraindicated. Less-experienced interventional radiologists (IRs) require an appropriate planning tool for the treatment to help avoid incomplete treatment and so reduce the tumour recurrence risk. Although a few tools are available to predict the ablation lesion geometry, the process is computationally expensive. Also, in our implementation, a few patient-specific parameters are used to improve the accuracy of the lesion prediction.

METHODS

Advanced heterogeneous computing using personal computers, incorporating the graphics processing unit (GPU) and the central processing unit (CPU), is proposed to predict the ablation lesion geometry. The most recent GPU technology is used to accelerate the finite element approximation of Penne's bioheat equation and a three state cell model. Patient-specific input parameters are used in the bioheat model to improve accuracy of the predicted lesion.

RESULTS

A fast GPU-based RFA solver is developed to predict the lesion by doing most of the computational tasks in the GPU, while reserving the CPU for concurrent tasks such as lesion extraction based on the heat deposition at each finite element node. The solver takes less than 3 min for a treatment duration of 26 min. When the model receives patient-specific input parameters, the deviation between real and predicted lesion is below 3 mm.

CONCLUSION

A multi-centre retrospective study indicates that the fast RFA solver is capable of providing the IR with the predicted lesion in the short time period before the intervention begins when the patient has been clinically prepared for the treatment.

Analysis of iodinated contrast delivered during thermal ablation: is material trapped in the ablation zone?

Intra-procedural contrast-enhanced CT (CECT) has been proposed to evaluate treatment efficacy of thermal ablation. We hypothesized that contrast material delivered concurrently with thermal ablation may become trapped in the ablation zone, and set out to determine whether such an effect would impact ablation visualization. CECT images were acquired during microwave ablation in normal porcine liver with: (A) normal blood perfusion and no iodinated contrast, (B) normal perfusion and iodinated contrast infusion or (C) no blood perfusion and residual iodinated contrast. Changes in CT attenuation were analyzed from before, during and after ablation to evaluate whether contrast was trapped inside of the ablation zone. Visualization was compared between groups using post-ablation contrast-to-noise ratio (CNR). Attenuation gradients were calculated at the ablation boundary and background to quantitate ablation conspicuity. In Group A, attenuation decreased during ablation due to thermal expansion of tissue water and water vaporization. The ablation zone was difficult to visualize (CNR  =  1.57  ±  0.73, boundary gradient  =  0.7  ±  0.4 HU mm(-1)), leading to ablation diameter underestimation compared to gross pathology. Group B ablations saw attenuation increase, suggesting that iodine was trapped inside the ablation zone. However, because the normally perfused liver increased even more, Group B ablations were more visible than Group A (CNR  =  2.04  ±  0.84, boundary gradient  =  6.3  ±  1.1 HU mm(-1)) and allowed accurate estimation of the ablation zone dimensions compared to gross pathology. Substantial water vaporization led to substantial attenuation changes in Group C, though the ablation zone boundary was not highly visible (boundary gradient  =  3.9  ±  1.1 HU mm(-1)). Our results demonstrate that despite iodinated contrast being trapped in the ablation zone, ablation visibility was highest when contrast is delivered intra-procedurally. Therefore, CECT may be feasible for real-time thermal ablation monitoring.

Fiber Optic Sensors for Temperature Monitoring during Thermal Treatments: An Overview

During recent decades, minimally invasive thermal treatments (i.e., Radiofrequency ablation, Laser ablation, Microwave ablation, High Intensity Focused Ultrasound ablation, and Cryo-ablation) have gained widespread recognition in the field of tumor removal. These techniques induce a localized temperature increase or decrease to remove the tumor while the surrounding healthy tissue remains intact. An accurate measurement of tissue temperature may be particularly beneficial to improve treatment outcomes, because it can be used as a clear end-point to achieve complete tumor ablation and minimize recurrence. Among the several thermometric techniques used in this field, fiber optic sensors (FOSs) have several attractive features: high flexibility and small size of both sensor and cabling, allowing insertion of FOSs within deep-seated tissue; metrological characteristics, such as accuracy (better than 1 °C), sensitivity (e.g., 10 pm·°C⁻¹ for Fiber Bragg Gratings), and frequency response (hundreds of kHz), are adequate for this application; immunity to electromagnetic interference allows the use of FOSs during Magnetic Resonance- or Computed Tomography-guided thermal procedures. In this review the current status of the most used FOSs for temperature monitoring during thermal procedure (e.g., fiber Bragg Grating sensors; fluoroptic sensors) is presented, with emphasis placed on their working principles and metrological characteristics. The essential physics of the common ablation techniques are included to explain the advantages of using FOSs during these procedures.

Radio Frequency Ablation

Radio frequency (RF) ablation is the latest and most promising treatment for nonsurgical cancer patients. This article will explain the history of how RF ablation was developed, moving us through the quest for larger ablations. It will take the reader step by step through the actual procedure; explain the different RF systems available; describe the physics of how RF ablation works and why it is preferred over other predecessors, such as cryoablation, microwave ablation, laser ablation, chemoablation, and ethanol ablation; and describe the pitfalls of each. It will also mention the reasons why ultrasonography is the most popular guidance method, while computed tomography is used for follow-up.