Photodynamic therapy is a kind of treatment which makes use of particular kind of light and a particular drug called the photosensitizing agent. When this drug is exposed to a certain wavelength of the said light, a form of oxygen is produced which has the power to kill the cells present nearby, including infected cells.
Each of the photosynthesizing drugs needs a specific wavelength of light to get activated. How far the light can reach within the body depends on the wavelength. Which drug needs to be administered and what wavelength of light needs to be used is something that doctors decide after carefully examining and analyzing the patient’s condition.
Use of photodynamic therapy (PDT) to treat cancer
PDT begins with a photosensitizing agent being injected into the patient’s bloodstream. Cells in the whole body absorb this agent, but it stays in the cancerous cells for a longer time than in the healthy, non cancerous cells. Within 1 to 3 days, almost whole of the agent leaves the normal cells in the body. Now, the tumor is treated with light, which gets absorbed by the photosensitizing agent to produce active oxygen. This active oxygen kills the cells nearby.
The light which is used for this therapy is generally from a laser. Other sources of light like light emitting diodes (LED) are also used sometimes. Fiber optic cables are used to direct laser light to internal parts of the patient’s body, like esophagus or lungs.
PDT not only kills cancer cells directly, it also helps destroy or check tumors by activating the immune system to fight cancerous cells in the tumor. Along with this, the photosensitizing drug has the power to damage blood vessels present in the tumor.
For PDT, the patients don’t need to be admitted in the hospital. PDT can be used in combination with other therapies like chemotherapy, radiation or surgery. PDT might also need to be repeated.
Which cancers can be treated with PDT?
Currently, the porfimer sodium or Photofrin is the FDA approved photosensitizing agent used in PDT to provide treatment for non-small cell lung cancer and esophageal cancer. In case of esophageal cancer, if the cancer blocks the esophagus, Porfimer sodium is used to provide relief from the resultant symptoms. Also, if laser therapy of esophageal cancer does not produce desired results, doctors may opt for PDT. In the case of non-small cell lung cancer, PDT is used when the cancer clocks airways or usual treatments are inadequate to treat the cancer.
Limitations of PDT
PDT has its own limitations. The light used in PDT is unable to cross more than a centimeter of tissue in the body. So, PDT can treat only those tumors which are either just below the skin or on the lining generally found on internal organs and cavities. As the light cannot travel across larger tumors, it cannot treat large tumors. Also, it cannot treat cancer that has metastasized and is more suited for local treatment.
Side-effects of PDT
Doctors advise patients to keep away from direct sunlight and bright lights for almost six weeks as the photosensitizing agent causes your skin and eyes to become sensitive to light.
Though PDT does not damage healthy tissues in the body, there could still be some burns, pain, swelling or scarring of the adjacent healthy cells. Patients could also experience coughing, pain in the stomach, shortness of breath or problems in swallowing, but these side-effects do not last long.
PDT and the future
Similar to other treatments for cancer, PDT is also the subject of continuous research so that it can be made more effective and can be used to treat other cancers also. Currently, some research studies are under way to assess if PDT can treat cancers like those of peritoneal cavity, cervix, prostate, skin and brain. There is also research going on to develop stronger photosensitizing agents and light that can travel more to treat larger tumors.