Lasers in rectosigmoid cancers: factors affecting immediate and long-term results

Abstract

Surgical segmental resection offers the best chance of cure in patients with rectosigmoid cancer. It is also the most effective form of palliation of local symptoms. Unfortunately, it can cause excessive morbidity and mortality in patients who have severe concomitant medical illness. For these patients, alternative methods of removing cancer are being studied for efficacy and risk. One important method of destroying rectosigmoid cancer uses laser energy. Laser is an acronym for light amplification of stimulated emission of radiation. The energy is monochromatic, coherent and collimated. It can be delivered through a quartz fibre passed down the instrument channel of an endoscope to focus the beam on a well demarcated area of tissue. At an appropriate intensity, laser energy creates heat in the tissue resulting in cell death at moderate temperatures and tissue vaporization at higher temperatures. The amount of heating depends on the wavelength, the irradiance, the pulse sequence and the spot size. The goal in laser ablation of cancer is to destroy the cancer cells while avoiding deeper injury to the intestinal wall which could result in perforation. The two most commonly used lasers for gastrointestinal tumour ablation are the argon laser and the Nd:YAG laser. The argon laser emits several wavelengths from 4W514 nm which is in the blue-green range of the visible light spectrum. Absorption is high in tissue and this results in superficial destruction without deeper injury. It is most useful in destroying smaller amounts of tissue with a high degree of precision. The Nd:YAG laser has an invisible wavelength of 1064nm and is poorly absorbed. There is much more penetration and diffusion of heat with the Nd:YAG laser than with the argon laser. The Nd:YAG laser is therefore more useful for destroying larger intraluminal areas of tumour. Rectosigmoid cancers which invade only superficially into the submucosa