Lasers in gastroenterology

Table 1 Laser effects used in gastroenterology

Laser effect	Clinical use
High power thermal:	Haemostasis
	Cutting or debulking of tissue by vaporisation and coagulation
Low power thermal: (Interstitial laser photocoagulation, ILP)	Gentle coagulation of lesions within solid organs
Photochemical: (Photodynamic therapy, PDT)	Non-thermal destruction of tissue by activation of a previously administered photosensitising drug
Pulsed shock wave	Fragmentation of gall stones

Table 2 Comparison of modalities for palliation of malignant dysphagia

	Laser	Conventional stent	Self expanding metal stent
Technique	Basically safe (risk of perforation if dilatation also needed)	10% risk of perforation on insertion	Usually safe and easy to insert
Cost	High setup cost Low patient costs	Low cost	High cost
Contra	Fistula	High lesion	High lesion
indications	No endoscopic target	Tracheal compression	Tracheal compression Care with lesions crossing cardia
Dysphagia post	Variable, can be	Semi-solids	Variable, can be
therapy	close to normal	some solids	close to normal
Repeat Therapy	Possible. Usually required after 6-8 weeks	Stent can be adjusted	Difficult to adjust once inserted. Second stent or laser debulking for tumour overgrowth
Enhancement of	Yes	No	No
dysphagia relief with radiotherapy

Table 3 Comparison of interstitial laser photocaogulation (ILP) and photodynamic therapy (PDT)

	ILP	PDT
Nature of biological effect	Thermal	Photochemical
Wavelength of light used	Infrared (805-1064 nm)	Green (510-530 nm) Red (630-675 nm)
Typical laser power per fibre	3-5 W	0.1-0.3 W (higher for illuminating hollow organs)
Effect on connective tissue	Destroyed	Largely unaffected
Healing	Resorption and scarring, some regeneration	Regeneration, sometimes with scarring
Selectivity of necrosis between tissue of origin of tumour and other adjacent tissues	None	Possible between mucosa and underlying muscle in hollow organs
Selectivity of necrosis between tumour and tissue of origin of tumour	None	Minimal
Cumulative toxicity	None	None

Table 4 Potential targets for photodynamic therapy in gastroenterology

Small, inoperable tumours in endoscopically accessible sites

Areas of dysplasia, especially in Barrett's oesophagus

Localised pancreatic cancer

Bile duct cancer

As an adjunct to surgery

Palliation of advanced cancers-controversial

Eradication of Helicobacter pylori-speculative