Multiple fiber laser-induced thermotherapy for ablation of large intrahepatic tumors

Automatic volumetric temperature regulation during in vivo MRI-guided laser-induced thermotherapy (MRg-LITT) with multiple laser probes

BACKGROUND

Clinical Laser-Induced Thermotherapy (LITT) currently lacks precise control of tissue temperature increase during the procedure. This study presents a new method to automatically regulate the maximum temperature increase in vivo at different positions by adjusting LITT power delivered by multiple laser probes using real-time volumetric MR-thermometry.

METHODS

The regulation algorithm was evaluated in vivo on a pig leg muscle. Temperature regulation was performed in volumes surrounding each laser probe tip. The power delivered to each laser probe was automatically adjusted every second using a feedback control algorithm by processing on-the-fly MR-thermometry images (10 slices/second) on a 1.5 T clinical scanner (1.56 mm × 1.56 mm x 3 mm resolution), using the proton-resonance frequency (PRF) shift technique. Several experimental conditions were tested with predefined temperature-time profiles corresponding to conditions of thermal ablation (+30 °C above body temperature) or moderate hyperthermia (+10 and + 15 °C). Control images were acquired after injection of Gadolinium at the end of experiment and were compared with the thermal dose images calculated from the thermometry images.

RESULTS

The mean difference and root mean squared error between target temperatures and measured ones remained below 0.5 °C and 2 °C respectively, for 5 min duration. Lesion sizes observed on thermal dose and on images acquired after gadolinium injection were in good agreement.

CONCLUSION

Automatic regulation of in vivo temperature increase during LITT procedures with multiple laser emitters control is feasible. The method provides an adaptative solution to improve the safety and efficacity of such clinical procedures.

Motion compensation for MRI-compatible patient-mounted needle guide device: estimation of targeting accuracy in MRI-guided kidney cryoablations

Patient-mounted needle guide devices for percutaneous ablation are vulnerable to patient motion. The objective of this study is to develop and evaluate a software system for an MRI-compatible patient-mounted needle guide device that can adaptively compensate for displacement of the device due to patient motion using a novel image-based automatic device-to-image registration technique. We have developed a software system for an MRI-compatible patient-mounted needle guide device for percutaneous ablation. It features fully-automated image-based device-to-image registration to track the device position, and a device controller to adjust the needle trajectory to compensate for the displacement of the device. We performed: (a) a phantom study using a clinical MR scanner to evaluate registration performance; (b) simulations using intraoperative time-series MR data acquired in 20 clinical cases of MRI-guided renal cryoablations to assess its impact on motion compensation; and (c) a pilot clinical study in three patients to test its feasibility during the clinical procedure. FRE, TRE, and success rate of device-to-image registration were 2.71 ± 2.29 mm, 1.74 ± 1.13 mm, and 98.3% for the phantom images. The simulation study showed that the motion compensation reduced the targeting error for needle placement from 8.2 mm to 5.4 mm (p  <  0.0005) in patients under general anesthesia (GA), and from 14.4 mm to 10.0 mm (p < 1.0 × 10(−5)) in patients under monitored anesthesia care (MAC). The pilot study showed that the software registered the device successfully in a clinical setting. Our simulation study demonstrated that the software system could significantly improve targeting accuracy in patients treated under both MAC and GA. Intraprocedural image-based device-to-image registration was feasible.

Tapered fiber optic applicator for laser ablation: Theoretical and experimental assessment of thermal effects on ex vivo model

Laser Ablation (LA) is a minimally invasive technique for tumor removal. The laser light is guided into the target tissue by a fiber optic applicator; thus the physical features of the applicator tip strongly influence size and shape of the tissue lesion. This study aims to verify the geometry of the lesion achieved by a tapered-tip applicator, and to investigate the percentage of thermally damaged cells induced by the tapered-tip fiber optic applicator. A theoretical model was implemented to simulate: i) the distribution of laser light fluence rate in the tissue through Monte Carlo method, ii) the induced temperature distribution, by means of the Bio Heat Equation, iii) the tissue injury, by Arrhenius integral. The results obtained by the implementation of the theoretical model were experimentally assessed. Ex vivo porcine liver underwent LA with tapered-tip applicator, at different laser settings (laser power of 1 W and 1.7 W, deposited energy equal to 330 J and 500 J, respectively). Almost spherical volume lesions were produced. The thermal damage was assessed by measuring the diameter of the circular-shaped lesion. The comparison between experimental results and theoretical prediction shows that the thermal damage discriminated by visual inspection always corresponds to a percentage of damaged cells of 96%. A tapered-tip applicator allows obtaining localized and reproducible damage close to spherical shape, whose diameter is related to the laser settings, and the simple theoretical model described is suitable to predict the effects, in terms of thermal damage, on ex vivo liver. Further trials should be addressed to adapt the model also on in vivo tissue, aiming to develop a tool useful to support the physician in clinical application of LA.

New therapeutic approaches to metastatic gastroenteropancreatic neuroendocrine tumors: A glimpse into the future

Neuroendocrine (NE) gastroenteropancreatic tumors are a heterogeneous group of neoplasias arising from neuroendocrine cells of the embryological gut. Their incidence have increased significantly over the past 3 decades probably due to the improvements in imaging and diagnosis. The recent advances in molecular biology have translated into an expansion of therapeutic approaches to these patients. Somatostatin analogs, which initially were approved for control of hormonal syndromes, have recently been proven to inhibit tumor growth. Several new drugs such as antiangiogenics and others targeting mammalian target of rapamycin pathways have been approved to treat progressive pancreatic neuroendocrine tumors (NETs) although their role in non-pancreatic is still controversial. The treatment of NETs requires a coordinated multidisciplinary approach. The management of localized NETs primarily involves surgical resection followed by surveillance. However, the treatment of unresectable and/or metastatic disease may involve a combination of surgical resection, systemic therapy, and liver-directed therapies with the goal of alleviating symptoms of peptide release and controlling tumor growth. This article will review the current therapeutic strategies for metastatic gastroenteropancreatic NETs and will take a glimpse into the future approaches.

Laser ablation for small hepatocellular carcinoma: State of the art and future perspectives

During the last two decades, various local thermal ablative techniques for the treatment of unresectable hepatocellular carcinoma (HCC) have been developed. According to internationally endorsed guidelines, percutaneous thermal ablation is the mainstay of treatment in patients with small HCC who are not candidates for surgical resection or transplantation. Laser ablation (LA) represents one of currently available loco-ablative techniques. In this article, the general principles, technique, image guidance, and patient selection are reported. Primary effectiveness, long-term outcome, and complications are also discussed. A review of published data suggests that LA is equivalent to the more popular and widespread radiofrequency ablation in both local tumor control and long-term outcome in the percutaneous treatment of early HCC. In addition, the LA technique using multiple thin laser fibres allows improved ablative effectiveness in HCCs greater than 3 cm. Reference centres should be equipped with all the available techniques so as to be able to use the best and the most suitable procedure for each type of lesion for each patient.

Tumor ablation: common modalities and general practices

Tumor ablation is a minimally invasive technique that is commonly used in the treatment of tumors of the liver, kidney, bone, and lung. During tumor ablation, thermal energy is used to heat or cool tissue to cytotoxic levels (less than -40°C or more than 60°C). An additional technique is being developed that targets the permeability of the cell membrane and is ostensibly nonthermal. Within the classification of tumor ablation, there are several modalities used worldwide: radiofrequency, microwave, laser, high-intensity focused ultrasound, cryoablation, and irreversible electroporation. Each technique, although similar in purpose, has specific and optimal indications. This review serves to discuss general principles and technique, reviews each modality, and discusses modality selection.

Design of fiber optic applicators for laser interstitial thermotherapy: theoretical evaluation of thermal outcomes

Thermal effects of different applicators for energy deposition in tissue undergoing laser interstitial thermotherapy (LITT) are investigated. The aim is to predict temperature distribution (T), dimensions and shape of thermal lesion produced by the laser light absorption within the tissue, in order to achieve an optimal design of the applicator for LITT. A numerical model, based on Monte Carlo method, was implemented to predict the distribution of laser light within the tissue, and the Bio Heat Equation was used to simulate T. Four geometries of optical applicators with different emitting surfaces were considered: bare fiber, cylindrical, zebra and a hybrid geometry. Effects on liver tissue undergoing LITT were evaluated in terms of T and coagulation volumes. Simulations were performed with laser power of 3 W and 5 W and energy of 1650 J. Results show that bare fiber causes an irregular coagulation shape; zebra and hybrid applicators 3 cm-long obtain an elliptical lesion, with lowest maximum T (Tmax) on their surface (about 350 K); cylindrical applicators with length of 1 cm or 1.5 cm produce spherical lesions, with Tmax up to 398 K. Results suggest that the selection of the applicator based on the geometry of the lesion could improve LITT outcome. Furthermore, an appropriate geometry can preserve applicator integrity avoiding excessive temperature increase on its surface.

A novel needle guide system to perform percutaneous laser ablation of liver tumors using the multifiber technique

BACKGROUND

Previous studies have shown that laser ablation with the multifiber technique is effective in the treatment of liver tumors. However, the correct positioning of multiple needles may be challenging.

PURPOSE

To investigate the use of a novel needle guide system that was developed to perform percutaneous laser ablation of liver tumors with the multifiber technique under ultrasonographic guidance.

MATERIAL AND METHODS

Between February 2009 and June 2011, 116 patients (104 hepatocellular carcinomas and 12 metastases) with 127 liver nodules (median diameter, 3.0 cm; range, 1.5-6.0) were treated. Nineteen nodules were in high-risk locations. A needle guide with separate channels to insert two needles in a parallel position and at a prefixed distance was used.

RESULTS

Needles were positioned inside the target nodule easily and quickly, and correct spacing (1.5-1.8 cm) between light sources was immediately achieved. Complete tumor ablation was achieved in a single session in 112 (88.2%) lesions. In nodules ≤3.0 cm and >3.0 cm in size, ablation was complete in 93.6% and 79.6% of cases, respectively. Of note, complete ablation was achieved in 91.7% of nodules up to 5.0 cm.

CONCLUSION

With the new guidance system, needles could be inserted in parallel fashion, which facilitated positioning the needles in geometrical configurations to maximize the ablative effect. Worthy of note, the complete ablation rate in nodules >3.0 cm using the new guide system was higher than what has been reported in the literature so far.

Temperature monitoring and lesion volume estimation during double-applicator laser-induced thermotherapy in ex vivo swine pancreas: a preliminary study

Tissue temperature distribution plays a crucial role in the outcome of laser-induced thermotherapy (LITT), a technique employed for neoplasias removal. Since recent studies proposed LITT for pancreatic tumors treatment, assessment of temperature and of its effects around the laser applicator could be useful to define optimal laser settings. The aims of this work are temperature monitoring and measurement of ablated tissue volume in an ex vivo porcine pancreas undergoing double-applicator LITT. A three-dimensional numerical model is implemented to predict temperature rise and volumes of ablated tissue in treated pancreas. Experiments are performed to validate the model, with two modalities: (1) 12-fiber Bragg grating sensors are adopted to monitor the heating and cooling during LITT at several distances from the applicators tip, and (2) 1.5-T MR imaging is used to estimate the ablated volume. Experimental data agree with theoretical ones: at 2 mm from both applicators tips, the maximum temperature increase is approximately 60 °C downward from the tips, while it increases of about 40 °C and 30 °C, respectively, at the level and upward from the tips. This behavior occurs also at other distances, proving that the tissue downward from the tip is mostly heated. Furthermore, the estimated volume with MRI agrees with theoretical one (i.d., 0.91 ± 0.09 vs. 0.95 cm(3)). The encouraging results indicate that the model could be a suitable tool to choose the optimal laser settings, in order to control the volume of ablated tissue.

Laser ablation for small hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide and is increasingly detected at small size (<5 cm) owing to surveillance programmes in high-risk patients. For these cases, curative therapies such as resection, liver transplantation, or percutaneous ablation have been proposed. When surgical options are precluded, image-guided tumor ablation is recommended as the most appropriate therapeutic choice in terms of tumor local control, safety, and improvement in survival. Laser ablation (LA) represents one of currently available loco-ablative techniques: light is delivered via flexible quartz fibers of diameter from 300 to 600 μm inserted into tumor lesion through either fine needles (21g Chiba needles) or large-bore catheters. The thermal destruction of tissue is achieved through conversion of absorbed light (usually infrared) into heat. A range of different imaging modalities have been used to guide percutaneous laser ablation, but ultrasound and magnetic resonance imaging are most widely employed, according to local experience and resource availability. Available clinical data suggest that LA is highly effective in terms of tumoricidal capability with an excellent safety profile; the best results in terms of long-term survival are obtained in early HCC so that LA can be proposed not only in unresectable cases but, not differently from radiofrequency ablation, also as the first-line treatment.

Principles of and advances in percutaneous ablation

Image-guided tumor ablation with both thermal and nonthermal sources has received substantial attention for the treatment of many focal malignancies. Increasing interest has been accompanied by continual advances in energy delivery, application technique, and therapeutic combinations with the intent to improve the efficacy and/or specificity of ablative therapies. This review outlines clinical percutaneous tumor ablation technology, detailing the science, devices, techniques, technical obstacles, current trends, and future goals in percutaneous tumor ablation. Methods such as chemical ablation, cryoablation, high-temperature ablation (radiofrequency, microwave, laser, and ultrasound), and irreversible electroporation will be discussed. Advances in technique will also be covered, including combination therapies, tissue property modulation, and the role of computer modeling for treatment optimization.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Opportunities for near-infrared thermal ablation of colorectal metastases by guanylyl cyclase C-targeted gold nanoshells

Colorectal cancer is the third most common malignancy and the second most common cause of cancer-related mortality worldwide. While surgery remains the mainstay of therapy, approximately 50% of patients who undergo resection develop parenchymal metastatic disease. Unfortunately, current therapeutic regimens offer little improvement to the survival of patients with parenchymal metastases in the liver and lung. In that context, there is a significant unrealized opportunity at the intersection of engineering and biology for the development of novel targeted therapeutic approaches to colorectal cancer metastases. This opportunity exploits the discovery that an intestinal receptor, guanylyl cyclase C, which mediates diarrhea induced by bacterial heat-stable enterotoxins (STs), is over-expressed by metastatic colorectal tumors only. Moreover, it leverages recent advances in the fabrication of metal nanoshells with defined thicknesses absorb near-infrared (NIR) light, resulting in resonance and transfer of thermal energies of more than 40 degrees C. Thus, the conjugation of ST to gold nanoshells, which can undergo resonance excitation by NIR light and emit heat, represents a previously unrecognized approach for the targeted therapy of parenchymal colorectal cancer metastases, specifically to the liver and lung. This article discusses the potential of ST-targeted nanoshells for NIR thermal ablation of metastatic colorectal tumors and highlights the significant challenges and solutions linked to the translation of this emerging technology to patient care.

Liver metastases of neuroendocrine tumours; early reduction of tumour load to improve life expectancy

Background

Neuroendocrine tumours frequently metastasize to the liver. Although generally slowly progressing, hepatic metastases are the major cause of carcinoid syndrome and ultimately lead to liver dysfunction, cardiac insufficiency and finally death.

Methods

A literature review was performed to define the optimal treatment strategy and work-up in patients with neuroendocrine hepatic metastases. Based on this, an algorithm for the management of these patients was established.

Results

Platelet serotonin and chromogranin A are useful biomarkers for detection and follow-up of neuroendocrine tumour. Helical computed tomography and somatostatin receptor scintigraphy are the most sensitive diagnostic modalities. Surgical debulking is an accepted approach for reducing hormonal symptoms and to establish better conditions for medical treatment, but is frequently impossible due to the extent of disease. A novel approach is the local ablation of tumour by thermal coagulation using therapies such as radiofrequency ablation (RFA) or laser induced thermotherapy (LITT). These techniques preserve normal liver tissue. There is a tendency to destroy metastases early in the course of disease, thereby postponing or eliminating the surgically untreatable stage. This can be combined with postoperative radioactive octreotide to eliminate small multiple metastases. In patients with extensive metastases who are not suitable for local destruction, systemic therapy by octreotide, ¹³¹I-MIBG treatment or targeted chemo- and radiotherapy should be attempted. A final option for selective patients is orthotopic liver transplantation.

Conclusion

Treatment for patients with neuroendocrine hepatic metastases must be tailored for each individual patient. When local ablative therapies are used early in the course of the disease, the occurrence of carcinoid syndrome with end stage hepatic disease can be postponed or prevented.