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It is branch of medicine that studies cancer tumours and seeks to understand their development, diagnosis, treatment and prevention. Lasers can be used in 2 ways to treat cancer.
To shrink or destroy a tumor with heat. To activate a chemical – known as a photosensitizing agent – that kills only the cancer cells. (This is called photodynamic therapy or PDT.)
Though lasers can be used alone, they are most often used with other cancer treatments, such as chemotherapy or radiation.
Lasers are also being studied for treating or preventing side effects of common cancer treatments. For instance, some studies are looking at how low-level laser therapy (LLLT) might be used to prevent or treat severe mouth sores caused by chemotherapy, and how they may be used to treat the swelling (lymphedema) that can result from breast surgery. Shrinking or destroying tumors directly
The CO2 and Nd:YAG lasers are used to shrink or destroy tumors. They can be used with thin, flexible tubes called endoscopes that let doctors see inside certain parts of the body, such as the bladder or stomach. The light from some lasers can be sent through an endoscope fitted with fiber optics. This lets doctors see and work in parts of the body that could not be reached otherwise except by major surgery. Using an endoscope also allows very precise aim of the laser beam.
Lasers can be used with low-power microscopes, too. This gives the doctor a larger view of the area being treated. When used with an instrument that allows very fine movement (called a micromanipulator), laser systems can produce a cutting area as small as 200 microns in diameter – that’s less than the width of a very fine thread.
Lasers are used to treat many kinds of cancer. In the intestines or large bowel, lasers can be used to remove polyps, small growths that might become cancer. The CO2 laser can be used to treat pre-cancerous tissue and very early cancers of the cervix, vagina, and vulva.
Lasers are also used to remove tumors blocking the swallowing tube (esophagus) and large intestine (colon). This does not cure the cancer, but it relieves some symptoms, such as trouble swallowing.
The Nd:YAG laser has also been used to remove cancer that has spread to the lungs from other areas. This helps avoid surgery that would require removing large sections of lung. This type of laser cannot cure cancer, but it can improve breathing and other symptoms in many patients.
Cancers of the head, neck, airways, and lungs can be treated (but usually not cured) with lasers. Small tumors on the vocal cords may be treated with lasers instead of radiation in some patients. Tumors blocking the upper airway can be partly removed to make breathing easier. Blockages deeper in the airway, such as in the branches of the breathing tubes (bronchi), can be treated with a flexible, lighted tube called a bronchoscope and an Nd:YAG laser.
Laser-induced interstitial thermotherapy (LITT) uses heat to help shrink tumors by damaging cells or depriving them of the things they need to live (like oxygen and food). In LITT, the laser light is passed through a fiber optic wire and right into a tumor, where it heats up, damaging or killing cancer cells. LITT is sometimes used to treat tumors in the liver. Photodynamic therapy
In photodynamic therapy (PDT), a special drug called a photosensitizing agent is put into the bloodstream. Over time it is absorbed by body tissues. The drug stays in cancer cells for a longer time than in normal tissue. Shining a certain kind of light on the cancer cells that have the drug in them “turns on” the drug, which then kills the cancer cells.
Photosensitizing agents are turned on or activated by a certain wavelength of light. For example, an argon laser can be used in PDT. When cancer cells that contain the photosensitizing agent are exposed to red light from this laser, it causes the chemical reaction that kills the cancer cells. Light exposure must be carefully timed so that it’s used when most of the agent has left healthy cells, but is still in the cancer cells.
Cancer cells can be singled out and destroyed but most normal cells are spared. The damaging effect of the photosensitizing agent happens only when the drug is exposed to light.The side effects are fairly mild.Still, PDT as it’s currently used is not without its problems. Argon laser light cannot pass through more than about 1 centimeter of tissue (a little more than one-third of an inch), which means it’s not useful against deeper tumors. And the photosensitizing agents used today can leave people very sensitive to light, causing sunburn-like reactions after only very brief sun exposure. This can greatly limit the patient’s activities until the body gets rid of the drug, which often takes weeks.
PDT is sometimes used to treat cancers and pre-cancers of the swallowing tube (esophagus), and certain kinds of lung cancer that can be reached with endoscopes. PDT is being studied for use in other cancers, such as those of the brain and prostate. Researchers also are looking at different kinds of lasers and new photosensitizer drugs that might work even better.
Photodynamic therapy or PDT is a treatment that uses special drugs, called photosensitizing agents, along with light to kill cancer cells. The drugs only work after they have been activated or “turned on” by certain kinds of light. PDT may also be called photoradiation therapy, phototherapy, or photochemotherapy.
Depending on the part of the body being treated, the photosensitizing agent is either put into the bloodstream through a vein or put on the skin. Over a certain amount of time the drug is absorbed by the cancer cells. Then light is applied to the area to be treated. The light causes the drug to react with oxygen, which forms a chemical that kills the cells. PDT might also help by destroying the blood vessels that feed the cancer cells and by alerting the immune system to attack the cancer.
The period of time between when the drug is given and when the light is applied is called the drug-to-light interval. It can be anywhere from a couple of hours to a couple of days, depending on the drug used.
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