The potential of laser-induced interstitial thermotherapy to treat liver metastases

Laser-induced interstitial thermotherapy (LITT) is a method which has becom e a promising alternative for the palliative treatment of non-resectable me tastases. At an early stage, a bare fibre was inserted, e.g, into liver met astases. Sophisticated applicators, with an integrated cooling system, are now used to increase the coagulated volume. The applicators can be introduc ed via laparotomy and laparoscopy under US-control, or percutaneously under CT- or MR-control. Most often, the Nd:YAG laser is used as the energy sour ce, because of its good penetration properties in biological tissue. There is a simultaneous increase of the temperature in the whole volume reached b y the laser radiation. This is a great advantage over cryotherapy and other thermal procedures, which are purely based on heat conduction. However, th e maximal diameter treated is limited by the blood perfusion, that takes aw ay a large amount of heat. Coagulation volumes of 35 mm in diameter can be reached. The coagulation zone can be controlled by US- CT- or MR-imaging. A cooled application system was designed and evaluated in an animal experime nt with pigs. The tissue repair reaction after coagulation is early fibrosi s. In the weeks following the treatment, the surrounding scar capsule, cons isting of fibrocytes, biliary ductules and collagen fibres, continuously en larges. Complications, such as bleeding, infection and liver failure, are n ot as frequent after LITT as after surgical resection. Since the coagulatio n process is non-ablative, even the area around big vessels can be treated, Due to the large heat transport by the blood flow, the wall of the vessel is not affected by thermal radiation. Therefore, even metastases close to t he vena cava or the portal vein are treatable. It has been shown that metas tases can principally be destroyed with this method. Randomised studies are needed to evaluate this method clinically and determine survival time and quality of life.