We have conducted a large-scale 14-year study that found laser ablation with MR guidance is very effective in the treatment of primary and metastatic liver tumors. We presented data from 1394 patients with 3725 lesions at the 2007 European Congress of Radiology. We have since ablated a total of 5041 lesions in 1954 patients. The two largest patient groups suffered from colorectal liver metastases and breast cancer liver metastases.
MR-guided laser-induced thermotherapy (LITT) is a minimally invasive procedure to ablate tumors using optical fibers to deliver high-energy laser radiation to the target lesion. Due to the light absorption, temperatures of up to 120ºC are reached within the tumor, leading to a substantial thermocoagulation (Figure 1). MR imaging is used to monitor the progress of thermocoagulation. The thermosensitivity of certain MR sequences is the key to real-time monitoring, allowing accurate estimation of the actual extent of the thermal damage.
The whole procedure, typically done under local anesthesia on an outpatient basis, takes between 60 and 90 minutes, from positioning the patient to CT-guided puncture, MR-guided tumor ablation, and finally removal of the laser application systems. The laser ablation itself takes between 10 and 30 minutes. Although MRI is the best modality for guiding the procedure, ultrasound also will work under certain conditions.
LITT offers several advantages over surgery and other types of ablation:
- Treatment can be done on an outpatient basis under local anesthesia. No hospitalization is necessary.
- The treatment can be repeated easily if follow-up studies show new metastases.
- If metastases occur in both liver lobes, all lesions can be ablated.
- Mortality and morbidity rates are both low.
- Multiple laser applications can be used in completely different parts of the liver simultaneously because the different laser applicators do not interact with one another. Therefore, two or three metastases can be ablated simultaneously using anesthesia on an outpatient basis.
Up to 70% of patients with colorectal cancer, which, in many countries, is among the most common cancers, eventually develop liver metastases. These metastases are confined to the liver at the time of diagnosis in 30% to 40% of these patients.
Until recently, the traditional treatment for primary or metastatic liver tumors was surgical resection. Only 25% of patients with liver metastases are candidates for surgery, however, because of the size, distribution, or accessibility of their tumors. The morbidity rate for surgery is high, and therapeutic alternatives are also needed because the incidence of new liver metastases following successful resection of metastases is high: between 60% and 80%.
GROWTH FACTORS
Studies have shown that large liver resections stimulate many growth factors, including those associated with micrometastases that may be located elsewhere in the liver. This is probably the reason why many patients develop new metastases in the first year after surgical resection. Stimulation of these growth factors after surgical resection may also encourage the development of new metastases outside the liver, for example, in the lung or lymph nodes.
