Fifty-five liver metastases in 21 patients were treated with interstitial laser photocoagulation (ILP). Tumors were irradiated with a neodymium yttrium aluminum garnet laser via optical fibers passed through 19-gauge needles inserted under ultrasound (US) guidance. Heating of the tumor was evident at real-time US as an expanding and coalescing echogenic zone around the needle tips. After ILP, dynamic computed tomography (CT) showed laser-induced necrosis as a new area of nonenhancement. Necrosis of tumor volume was more than 50% in 82% (45 of 55) of the tumors, and 100% necrosis was achieved in 38% (21 of 55). Metastases smaller than 4 cm in diameter were treated more effectively and required fewer treatment sessions than did those larger than 4 cm. Complications were minor and included severe pain in four cases, persistent pain for up to 10 days in 11 cases, and asymptomatic subcapsular hematoma (four cases) and pleural effusion (six cases) seen with CT. ILP is safe and effective for liver tumor destruction, and US and CT are useful in different aspects of treatment monitoring.

Summary The palliative management of hepatic metastases remains unsatisfactory. There is a need for a simple non invasive technique which can stop or retard the rate of tumour growth. In principle, Interstitial Laser hyperthermia may fulfil such a role. In experimental studies, this technique produced precise in situ necrosis within solid organs which healed safely. In a pilot feasibility study, we treated ten patients with a total of 18 hepatic metastases on 31 occasions using a percutaneous approach to achieve an overall objective response rate of 44%. The treatment proved simple to perform, was well tolerated and produced radiological evidence of necrosis in small metastases (diameter < 3 cm). However, further research is required before the technique can be regarded as established. Its future role in most cases will be to control the growth of discrete hepatic metastases unsuitable for resection. In instances where the extent of necrosis can be matched accurately to tumour volume, the potential for cure exists.Interstitial Laser Hyperthermia (ILH), an exciting new technique first described in 1983 using the Neodymium: YAG laser (Nd:YAG), is simple both in concept and execution (Bown, 1983). Its basis is the ability to transmit the infra red wavelength of YAG laser light (1064 nm)-an intense energy source, down thin calibre (0.1-0.6 mm) flexible silica or glass fibres with virtually no energy loss. Such small fibre diameters cause negligible tissue damage from their insertion. The light emitting end can be delivered percutaneously into the centre of solid organs (interstitial placement) within the peritoneal cavity using ultrasound guidance with minimal disturbance to the overlying abdominal wall. In contrast to the high powers (50-70 watts) and short exposure times (< 1.0 s) used with the Nd:YAG laser to recanalise obstructing foregut cancers, ILH requires much lower powers (0.5-2.0 watts) with long exposure times (200-1000 s). The laser light is therefore delivered in a more gentle and controlled manner to be absorbed as heat producing a zone of tissue necrosis centred around the fibre tip. The treated area is left in situ to undergo resorption with healing by regeneration and/or fibrosis. In the field of oncology, the prospect of achieving accurate in situ necrosis of malignant tissue simply and atraumatically may obviate, in certain instances, the necessity for surgical excision with its attendant hazards and cost.Experimental work using a single fibre positioned at laparotomy in normal rat liver has produced well defined, reproducible areas of necrosis up to 15 mm in diamter; the diameter being a function of the applied laser power and exposure times (Matthewson et al., 1987). Similar intraoperative studies have also been performed in canine liver using four fibres in juxtaposition fired simultaneously from a single laser (Steger et al., 1988). At 1 week, well defined confluent areas of necrosis up to 3.5 cm in diameter were obtained. These were roughly spherical and centred around the fibres. Such areas...

Experimental studies have shown that once the appropriate laser parameters are defined, interstitial laser hyperthermia (ILH) can produce well-defined, predictable tissue necrosis in solid viscera which heal safely with little functional or structural sequelae. Preliminary clinical studies have illustrated that ILH is simple to perform, is well tolerated producing radiological and histological evidence of necrosis in liver, pancreatic, and breast cancer. Its future role in most cases will be palliative, controlling local tumour growth. Where the extent of necrosis can be matched accurately to tumour volume, the prospect for cure exists. Further research is necessary before ILH can be regarded as an established treatment and, in particular, its influence on patient survival is worthy of further evaluation.

Conventional palliative management of inoperable focal hepatic tumours remains unsatisfactory. Interstitial techniques such as cryotherapy, alcohol injection, low power laser hyperthermia and interstitial radiotherapy offer alternative approaches. Cryotherapy is an effective and precise technique for inducing tumour necrosis. It can only be performed at laparotomy making it relatively invasive and retreatment impractical. Alcohol is cheap and can be injected percutaneously. However, inhomogeneous distribution produces imprecise and nonreproducible lesions. Low power laser hyperthermia produces precise and reproducible areas of necrosis that are roughly spherical in shape. At present, this technique is most effective for small tumours. Interstitial radiotherapy remains the least evaluated of all the interstitial techniques. Unlike cryotherapy and low power laser hyperthermia, the biological effect of ethanol injection and interstitial radiotherapy cannot be monitored in real time by ultrasound. With the exception of cryotherapy, all methods can be applied percutaneously with low morbidity and mortality. None of these techniques is established, but they may offer the prospect of cure in cases where all areas of tumour can be positively identified and fully treated. However, in most instances the intention is to control the growth of relatively small discrete volumes of tumour within the hepatic parenchyma.

No abstract