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LASERS IN G-1 ONCOLOGY Ravi Kant, MS, DNB; Bina Ravi, MS, MNAMS Professor
of Surgery/Oncology, Maulana Azad Medical College, New Delhi. The principle of heat to treat maladies is known since antiquity. However, the ancient methods were not only crude and of unpredictable response but also, the inaccessible areas of the body were beyond their purview. LASER is an acronym for Light Amplification by stimulated Emission of Radiation Laser Safety: Most of the clinical lasers are grouped as Class IV laser where safety precautions are mandatory. Most dangerous is the permanent blindness of the eye. Each type of wave length needs a different density of spectacles. The injuries could be unintended explosions, burns, inappropriate treatment, smoke and vapour. Smoke evacuators must be routinely used. UNINTENDED INJURIES: Perforation of viscera, thermal injury due to scattered reflected or direct laser beam, ignition of volatile gases, dry drapes, plastic canula and inappropriate treatment due to unskilled use. EYE INJURY: Commonly available eye wear will not protect the eye wear designed to use with laser equipment, mention the wavelength against which the eye wear is effective and this should be checked without fail. It is the responsibility of the surgeon to ensure that everyone in operating room including patient, anesthetists, nurses and assistants are wearing protective eyewear. An automatic lock on the entrance of operation suite is essential. Laser Tissue Interaction: Laser tissue interaction may be photothermal photocoagulative, hyperthermia, photodynamic, photomechanical, photodisruption, photoaccoustics, or photochemical. Laser therapy of oesophageal and gastric lesions: A far more superior quality of life is achieved when laser assisted tunneling of blocked esophageal cancer, guided by endoscopic ultrasound and realtime imaging is done by Non Contact Nd YAG Laser at 50 - 70 W. The contact probes produce unacceptable perforations and are used by very few skilled operators only. The three golden rules of SG Bown are. 1) Keep the tip out of endoscope or else the endoscope is destroyed . 2) Point the red He-Ne aiming beam on the target and visibly identify it. 3) Never allow the laser fibre tip to touch the tumour tissue or else perforation is likely to occur. The Japanese have advocated Endoscopic laser therapy for early gastric cancer, confined to mucosa, where endoscopic ultrasound shows no lymph node metastasis. Laser therapy of colorectal Carcinoma: Tunneling with the help of laser thought the flexible videoendoscope may avoid the need of emergency colostomy and THC (Tholium - Holmium Chromium) YAG laser at 2150 nm is useful in treatment of sessile polyps. Laser fibre of pulsed Dye laser can be negotiated through the flexible colonoscope for photodynamic therapy of colonic tumours. Post radiation rectal bleed is easily treated by 1064 nm ND YAG laser at 25 - 30 W. Laser Assisted Liver Resection: This is helpful in nonanatomical as well as anatomical resections. A combi laser incorporating CO2 and ND YAG or the latter alone in contact mode, using sapphire frosted tip at 15W is used. Argon beam coagulator in hands of experienced hepatic surgeons is faster to operate. Argon beam can coagulate upto the depth of 2.4 mm and needs a gas flow upto 12L/minute. A theoretical possibility of potential spread of tumour by gas flow and air embolisation exists with the Argon beam coagulator. Interstitial Laser Hyperthermia: Low power laser treatment of deep seated lesions, can be approached with the help of imaging techniques. Photodynamic Therapy: Photodynamic therapy involves interaction of laser light of specific wavelength with a photosensitiser dye given prior to therapy. Photodynamic Effect: Following the absorption of the light, the sensitiser is transformed from its ground state (singlet state) into an electronically excited state (triplet state) via a short lived excited singlet state. The excited triplet can produce oxygenated products (Type II reaction). The singlet oxygen is the highest toxic species to the cells and to the vasculature of tumour. This is a threshold effect and a certain quantity of singlet oxygen must be produced before a cell is killed. The photosensitiser molecules then return to the ground state and can be activated again. Laser assisted welding: The Exoscope, the automated dosimetry using 1.32 Nd-YAG, and milliwatt CO2 laser have been used for tissue fusion like anastomosis of vas deferens artery, trachea and bowel. Newer Lasers: Diode laser is portable and it is as effective as Nd-YAG laser. It is a solid state laser thus breakdown is significantly less. Mild infrared lasers, excimer lasers and THC YAG lasers are the new but significant advances in laser technology. Flexible fibres for CO2 laser like Zirconium fluoride, arsenic selenide glass fibre, silver halide and thallium salts or the dielectric coated hollow waveguides are now available. Lasers and Robots: Almost all interventional probes are likely to have a sensor which may incorporate ultrasonic probe besides probes for temperature and spectroscopic details. Once fed to computers, a logical conclusion will be robotic laser therapy, far exceeding the accuracy of human beings - the beginning of which is the automated treatment of skin haemangioma by Strathclyde University Glasglow. Summary: the lasers are a potent tool. Modern technolgy has significantly changed the patient management. The role of photodynamic therapy is likely to be promising and exciting event in this modern era of minimal invasive surgery. References:
Proceeding of 12th Annual Meeting of American Society for Laser Medicine and Surgery Lasers in surgery and Medicine Supplement 4, Abst. No. 127 p 32, 1992. |
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