Effect of blood flow occlusion on laser hyperthermia for liver metastases

EUS-RFA of the pancreas: where are we and future directions

Surgical resection remains the gold standard for pancreatic cancer, high-risk pancreatic neuroendocrine tumors (PNETs) and pancreatic cystic neoplasms (PCNs). However, a majority of pancreatic cancers are unresectable at the time of diagnosis. In addition, surgical resection of pancreatic lesions can be associated with morbidity and mortality. A less-invasive alternative therapeutic intervention to avoid short term and long-term adverse events is desirable, as is a minimally-invasive palliative therapy for unresectable or recurrent pancreatic cancers. Endoscopic ultrasound guided radiofrequency ablation (EUS-RFA) allows for selective tissue ablation with minimal injury to the surrounding tissue. EUS-RFA of pancreatic tumors has shown high clinical and technical success with acceptable side effects in pancreatic lesions, lymph nodes, and the celiac plexus. This paper will review the pathophysiology, available technology, safety and efficacy, and future directions of EUS-RFA.

Fiber Optic Sensors-Based Thermal Analysis of Perfusion-Mediated Tissue Cooling in Liver Undergoing Laser Ablation

The current challenge in the field of thermo-ablative treatments of tumors is to achieve a balance between complete destruction of malignant cells and safeguarding of the surrounding healthy tissue. Blood perfusion plays a key role for thermal ablation success, especially in the case of highly vascularized organs like liver. This work aims at monitoring the temperature within perfused swine liver undergoing laser ablation (LA). Temperature was measured through seven arrays of Fiber Bragg Grating sensors (FBGs) around the laser applicator. To mimic reality, blood perfusion within the ex-vivo liver was simulated using artificial vessels. The influence of blood perfusion on LA was carried out by comparing the temperature profiles in two different spatial configurations of vessels and fibers. The proposed setup permitted to accurately measure the heat propagation in real-time with a temperature resolution of 0.1 °C and to observe a relevant tissue cooling near to the vessel up to 65%.

Noninvasive Dynamic Imaging of Tumor Early Response to Nanoparticle-mediated Photothermal Therapy

In spite of rapidly increasing interest in the use of nanoparticle-mediated photothermal therapy (PTT) for treatment of different types of tumors, very little is known on early treatment-related changes in tumor response. Using graphene oxide (GO) as a model nanoparticle (NP), in this study, we tracked the changes in tumors after GO NP-mediated PTT by magnetic resonance imaging (MRI) and quantitatively identified MRI multiple parameters to assess the dynamic changes of MRI signal in tumor at different heating levels and duration. We found a time- and temperature-dependent dynamic change of the MRI signal intensity in intratumor microenvironment prior to any morphological change of tumor, mainly due to quick and effective eradication of tumor blood vessels. Based on the distribution of GO particles, we also demonstrated that NP-medited PTT caused heterogeneous thermal injury of tumor. Overall, these new findings provide not only a clinical-related method for non-invasive early tracking, identifying, and monitoring treatment response of NP-mediated PTT but also show a new vision for better understanding mechanisms of NP-mediated PTT.

Thermal ablation of tumours: biological mechanisms and advances in therapy

Minimally invasive thermal ablation of tumours has become common since the advent of modern imaging. From the ablation of small, unresectable tumours to experimental therapies, percutaneous radiofrequency ablation, microwave ablation, cryoablation and irreversible electroporation have an increasing role in the treatment of solid neoplasms. This Opinion article examines the mechanisms of tumour cell death that are induced by the most common thermoablative techniques and discusses the rapidly developing areas of research in the field, including combinatorial ablation and immunotherapy, synergy with conventional chemotherapy and radiation, and the development of a new ablation modality in irreversible electroporation.

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.

Changes in growth factor levels after thermal ablation in a murine model of colorectal liver metastases

OBJECTIVES

This study examines changes in the expression of growth factors following thermal ablation (TA) of selected colorectal cancer (CRC) liver metastases.

METHODS

Using mice with established CRC liver metastases, two tumours in each animal were thermally ablated. Liver and tumour tissues were collected at various time-points (days 0, 1, 2, 3, 5 and 7) following TA treatment from the ablation site and from sites distant from ablated tumour. Changes in growth factor expression (epidermal growth factor [EGF], vascular endothelial growth factor [VEGF], hepatocyte growth factor [HGF] and transforming growth factor-β[TGF-β]) in comparison with baseline levels (non-ablated) were assessed by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry.

RESULTS

Baseline TGF-β and VEGF levels in the liver parenchyma of tumour-bearing mice were significantly higher than levels in naive liver parenchyma. Levels of VEGF and HGF decreased after TA treatment in all tissues. Levels of EGF decreased in ablated and distant tumour tissues, but displayed a tendency to increase in liver tissue. Levels of TGF-β also decreased during the first 2 days following TA, but later increased in liver and tumour tissues distant from the ablation site to a level that reached significance in tumour tissue at day 7 (P < 0.001). Decreases in growth factor levels were also observed in animals that underwent laparotomy without TA treatment, which indicates that these decreases were caused by the experimental procedure.

CONCLUSIONS

Tumour induces upregulation of TGF-β and VEGF in liver parenchyma. Growth factors decreased after TA, but this appears to be the result of the experimental procedure rather than the TA itself. However, TA resulted in increased levels of TGF-β, which may contribute to tumour recurrence.

Laser ablation of hepatocellular carcinoma-A review

A wide range of local thermal ablative therapies have been developed in the treatment of non resectable hepatocellular carcinoma (HCC) in the last decade. Laser ablation (LA) and radiofrequency ablation (RFA) are the two most widely used of these. This article provides an up to date overview of the role of laser ablation in the local treatment of HCC. General principles, technique, image guidance and patient selection are discussed. A review of published data on treatment efficacy, long term outcome and complication rates of laser ablation is included and comparison with RFA made. The role of laser ablation in combination with transcatheter arterial chemoembolization is also discussed.

IMPACT OF BLOOD FLOW OCCLUSION ON LIVER NECROSIS FOLLOWING THERMAL ABLATION

BACKGROUND

Laser, radiofrequency and microwave are common techniques for local destruction of liver tumours by thermal ablation. The main limitation of thermal ablation treatment is the volume of necrosis that can be achieved. Blood flow occlusion is commonly advocated as an adjunct to thermal ablation to increase the volume of tissue necrosis based on macroscopic and histological assessment of immediate or direct thermal injury. This study examines the impact of blood flow occlusion on direct and indirect laser induced thermal liver injury in a murine model using histochemical methods to assess tissue vitality.

METHODS

Thermal ablation produced by neodymium yttrium-aluminium-garnet laser (wavelength 1064 nm) was applied to the liver of inbred male CBA strain mice at 2 W for 50 s (100 J). Treatment was performed with and without temporary portal vein and hepatic artery blood flow occlusion. Animals were killed upon completion of the procedure to assess direct thermal injury or at 24, 48 and 72 h to assess the progression of tissue damage. The maximum diameter of necrosis was assessed by vital staining for nicotinamide adenine dinucleotide (NADH) diaphorase. Microvascular changes were assessed by laser Doppler flowmetry, confocal in vivo microscopy and scanning electron microscopy.

RESULTS

The direct thermal injury (mean SE) assessed by NADH diaphorase staining was significantly greater following thermal ablation treatment without blood flow occlusion than with blood flow occlusion (3.3 (0.4) mm vs 2.9 (0.3) mm; P = 0.005). Tissue disruption, cracking and vacuolization was more pronounced adjacent to the fibre insertion site in the group treated with thermal ablation combined with blood flow occlusion. There was an equivalent increase in the extent of injury following therapy in both groups that reached a peak at 48 h. The maximum diameter of necrosis in the thermal ablation alone group at 48 h was significantly greater than the thermal ablation combined with blood flow occlusion group (5.8 (0.4) mm vs 5.3 (0.3) mm; P = 0.011). The patterns of microvascular injury were similar in both groups, varying in extent.

CONCLUSION

Temporary blood flow inflow occlusion appears to decrease the extent of initial injury measured by vital staining techniques and does not alter the time sequence of progressive tissue injury following thermal ablation therapy.

Patterns of heat shock protein (HSP70) expression and Kupffer cell activity following thermal ablation of liver and colorectal liver metastases

The time course and extent of thermal ablative injury differs in liver compared to tumour tissue. This may be influenced by differences in the expression of heat shock proteins (HSP) and the response of Kupffer cells to thermal injury. This study determines the expression and response of HSP70 and Kupffer cells to thermal ablative injury in a Murine model of colorectal liver metastases. Thermal ablation by laser (Nd-YAG wavelength 1064 nm) was induced in liver and colorectal cancer liver metastases in CBA strain mice. Laser energy was applied at 2 W for 50 s and produced incomplete tumour ablation. Established tissue injury was assessed in separate groups of animals at time points ranging from 12 h to 21 days following therapy. HSP70 and Kupffer cell expression at the margins of coagulated tissue was determined by immunohistochemical staining for HSP70 and F4/80 antigens, respectively. HSP70 was faintly expressed in the cytoplasm of all tumour cells, with distinct clusters exhibiting intense cytoplasmic and nuclear HSP70 staining (130+/-19 cells mm-2). Comparatively, HSP70 expression was uncommon in untreated control liver specimens (2+/-2 cells mm-2, p<0.001). Thermal ablation increased expression of HSP70 at coagulated tissue margins. The peak response in tumours occurred at 2 days post-ablation and was significantly greater than the peak response in liver, occurring at 12 h (809+/-80 cells mm-2 vs. 454+/-52 cells mm-2, p<0.001). HSP70 expression remained significantly elevated for 7 days following therapy in tumour tissue, compared to 3 days in liver. Kupffer cell numbers in untreated control tumours were significantly lower than in untreated control livers (285+/-23 cells mm-2 vs. 451+/-30 cells mm-2, p<0.001). Following thermal ablation, there was an initial decrease in Kupffer cell numbers at the margin of coagulation with subsequent persistent increases thereafter. In liver tissue, the peak Kupffer cell response occurred at 5 days post-therapy and was significantly greater than the peak response in tumour tissue 3 days post-thermal ablation (1074+/-34 cells mm-2 vs. 860+/-53 cells mm-2, p=0.007). Thermal ablation produces a greater and more prolonged HSP70 response in colorectal liver metastases than in liver tissue. It also induces persistent increases in Kupffer cell activity in liver and tumour tissue.

Mechanisms of Focal Heat Destruction of Liver Tumors

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

BACKGROUND AND OBJECTIVES

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

STUDY DESIGN/MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Effectivity of laser-induced thermotherapy: In vivo comparison of arterial microembolization and complete hepatic inflow occlusion

BACKGROUND AND OBJECTIVES

Laser-induced thermotherapy (LITT) is a promising method for local treatment of liver metastases. The aim of this study was to compare the effect of LITT on lesion size when combined with hepatic arterial microembolization or complete hepatic blood flow occlusion.

STUDY DESIGN/MATERIALS AND METHODS

In a porcine liver model, LITT (30 W 15 minutes) was performed with either normal (n = 12), partially interrupted (arterial microembolization via a hepatic artery catheter n = 12) or completely interrupted hepatic perfusion (Pringle's maneuver, n = 12). LITT lesions were macro- and microscopically assessed after liver dissection.

RESULTS

Hepatic inflow occlusion led to a fourfold increase in lesion volume after arterial microembolization and a ninefold increase after complete interruption (6.3. cm3 vs. 27.1 cm3 vs. 58.8 cm3, P < 0.01).

CONCLUSIONS

Interrupting hepatic perfusion significantly increases lesion volumes in LITT. This beneficial effect can also be achieved in the percutaneous application mode by LITT combined with arterial microembolization via a hepatic artery catheter.

Interstitial laser thermotherapy for liver tumours

BACKGROUND

Primary hepatocellular carcinoma (HCC) and metastases from colorectal cancer are the most common malignant liver tumours. Surgical resection is the optimum treatment in suitable patients. Interstitial laser thermotherapy (ILT) is gaining acceptance for the treatment of irresectable liver tumours and as a potential alternative to surgery. An understanding of the principles of therapy and review of clinical outcomes may allow better use of this technology.

METHOD

An electronic search using the Medline database was performed for studies on the treatment of hepatic malignancy published between January 1983 and February 2003.

RESULTS

Current information on the efficacy of ILT is based on prospective studies. ILT appears to be a safe and minimally invasive technique that consistently achieves tumour destruction. The extent of destruction depends on the fibre design, delivery system, tumour size and tumour biology. Real-time magnetic resonance imaging provides the most accurate assessment of laser-induced tumour necrosis. In selected patients with HCC and colorectal cancer liver metastases, ILT achieves complete tumour necrosis, provides long-term local control, and improves survival, compared with the natural history of the disease. In addition, ILT has survival benefits for patients with other tumour types, especially those with isolated liver metastases from a breast cancer primary.

CONCLUSION

ILT improves overall survival in specific patients with liver tumours. Advances in laser technology and refinements in technique, and a better understanding of the processes involved in laser-induced tissue injury, may allow ILT to replace surgery as the procedure of choice in selected patients with liver malignancies.