Principles and techniques of liver tumor ablation: laser induced thermotherapy

The liver plays a central role in the human metabolism and thus represents one of the organ systems most often affected, especially by tumor diseases. In the following the basics and data will be presented both for treatment aspects of secondary and primary liver tumors: Two thirds of the patients with colorectal carcinoma (CRC) have liver metastases by the time of death [57]. For CRC hepatic metastases, survival is determined by the number and extent of metastases. In untreated patients with liver metastases of CRC the median survival time is from 4.5 to 15 months [57]. Only 5-10% of all patients with liver metastases of CRC are suitable for resection [23,42,43]. After resection, the 5-year survival time improves from 16% to 40%. Only 20-30% of patients undergoing liver resection will remain free from tumor recurrence [57]. Up to now the liver resection of solitary lesions has been the only potential curative treatment. However, the high rate of intrahepatic relapses and a possible potentising of the intrahepatic growth in metastases as part of the tumor stimulation process by released tumor cells is considered problematic .In modern oncology systemic treatment options like chemotherapy and immunotherapy are increasingly supplemented by regional treatment options such as surgery and radiotherapy, and interventional oncological options such as thermal ablation and locoregional chemotherapy [36,45]. Hepatocellular carcinoma (HCC) is one of the most common malignant neoplasms. In the case of hepatocellular carcinoma (HCC), when the tumor is at an appropriate stage, liver resection or hemihepatic resection or liver transplant is the essential curative treatment [7,18,40]. In patients with a single small HCC and well-preserved liver function surgical resection provides a 5-year survival ranging from 47.160.5% [7,18,40]. However, most HCCs are unresectable because of underlying poor liver function or tumor multifocality. For small, unresectable HCC nodules the transplantation is effective with 83% remaining free of recurrence, and a survival rate at 4 years with a 6% peri-operative mortality. If there are contraindications, transarterial chemoembolisation is used as a palliative therapeutic strategy. Interstitial procedures such as MR-guided laser-induced thermotherapy or radiofrequency ablation show a high rate of controlling the site of the tumor. Within the last decade thermal ablations have been developed and clinically improved. Different technologies have been evaluated like magnetic resonance-guided laser-induced thermotherapy (MR-guided LITT), radiofrequency ablation (RF), microwave and cryotherapy. For this reason, there has been great interest in further developments of interstitial procedures such as laser coagulation or radiofrequency ablation over the last few years. Laser-induced interstitial thermotherapy (LITT) is a minimal invasive locoregional form of treatment, the coagulative effects of which lead to tumor destruction in solid organs [54-63]. Due to the comparatively high penetrative depth of the photons and the possibility of problem-free radiation transmission by fiber-optic waveguides, nearly infra-red lasers (NIR) are used for LITT. LITT provides a photothermal tumor destruction technique, permitting solid tumor configurations inside parenchymatous organs to be destroyed. The expansion of the tissue-destroying effect is dependent on the choice of radiation capacity and radiation time. This means that the parameters must be pre-selected in such a way that all tumor cells, if possible, are exposed to the coagulative effect. Besides, there must also be a safety margin of at least 5-10 mm in width. In order to do justice to the coagulation of a 3-dimensional tumor geometry, it must be possible to heat an approximately spherical volume of tissue at the same time. For this reason application systems of defined space radiation characteristics have been developed, the distal ends of which are prepared in such a way that the result is an even circumference of radiation. In the following we will present the experimental and clinical data for the MR-guided laser-induced thermotherapy of malignant liver tumors, focusing on liver metastases and primary hepatocellular carcinoma.