The use of therapeutic lasers depends on four basic laser-tissue interactions; photothermal, photochemical (PDT), mechanical and ablative. There is no place for mechanical and ablative interactions in oncology; PDT will be the subject of a further review and the subject of this review is therefore the photothermal reaction. Thermal lasers have been in routine use in oncology for the last 10-15 years. These lasers, emitting in the visible or infra-red parts of the spectrum, are used to produce three basic effects; hyperthermia, coagulation and vaporization. Other energy sources beside lasers can also be used to produce these tissue effects but lasers seem to possess certain basic advantages. In comparison with monopolar or bipolar diathermy and heater probes, lasers can deliver more power, more accurately at the target tissue with better control of damage and a wider range of effects. In comparison with microwave and ultrasound therapy, lasers are again more precise and can be used with more compact and accurate delivery devices. In gastroenterological surgery (as opposed to endoscopy), neurosurgery and gynaecology, laser light can be delivered via a handpiece to cut and coagulate. In ENT and also some applications of gynaecology lasers can also be used via a microscope. In endoscopic surgery laser light is delivered through an optical fibre within the endoscope - this for the time being precludes the use of the CO2 laser for these applications. More recently, the laser fibre can be placed directly within tumour tissue for interstitial thermal therapy of liver metastases, pancreatic tumours and brain tumours. The future use of thermal lasers in oncology depends very much on the results of properly controlled comparative studies against PDT and non-laser thermal devices; in addition their use may well be widened to include some curative procedures; up until now their use has very much been restricted to palliative therapy except where they are used as an adjunctive cutting device alongside conventional curative surgery.
