Amin, Zahir; (1994) Interstitial laser photocoagulation of liver metastases. Doctoral thesis (M.D), UCL (University College London).

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Abstract

The treatment of liver metastases is presently unsatisfactory; many patients receive no specific therapy because of the significant morbidity associated with current treatments which have no proven survival advantage. Interstitial laser photocoagulation (ILP) is a percutaneous technique of in situ liver tumour destruction by heat, using low power laser energy which is delivered via thin flexible optical fibres. In this thesis the potential of ILP to effectively treat liver metastases was investigated, and the aims of the thesis were: (a) to clarify the mechanism of action of ILP; (b) to improve the laser parameters and safely increase the extent of thermal damage; (c) to accurately assess the extent of thermal damage radiologically and histologically; (d) to evaluate the clinical application of ILP. One hundred and fifty six Wistar rats and two Large White pigs had ILP to their livers. The parameters evaluated were fibre size and material, different laser wavelengths, and fibre-tip alterations. Significant findings were that tissue charring around the fibre-tip was associated with greater thermal damage, and that new less penetrating wavelengths produced larger necrotic lesions than the 1064nm wavelength, contrary to previously held beliefs. Histological assessment demonstrated the unexpected finding of a zone of heat-fixed hepatocytes, outside which were necrotic cells. A computed tomography (CT)-pathologic study showed that the extent of the tissue density changes seen on CT corresponded to the extent of thermal damage pathologically. Ninety three liver metastases in 31 patients were treated with ILP. Monitoring by ultrasound showed the thermal change as an irregular echogenic zone during ILP, and dynamic CT demonstrated the laser-induced necrosis as a new area of non-enhancement 24hrs or more afterwards. Necrosis of tumour volume was more than 50% in 89% (83 of 93) of the tumours, and 100% necrosis was achieved in 55% (51 of 93). Tumours smaller than 4cm were treated more effectively than larger tumours. Complications were minor. ILP continues to evolve as a minimally invasive technique of in situ tumour destruction. This thesis highlights important new concepts on the mechanism of action of ILP, and the clinical evaluation has shown that ILP can, at present, safely and effectively destroy small liver metastases (2cm or less in diameter). The current drawbacks of the technique are discussed and potential solutions suggested.

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