Phototherapy (light therapy) has been used for more than a hundred years to treat cancer. Sonotherapy (sound therapy) is a relatively newer approach.2 Sono-Photodynamic therapy is a cancer treatment that uses a particular type of sound and light along with a sensitizing agent to destroy cancer cells.1 How does this cancer treatment work? What are its benefits and potential complications?
What is Sono-Photo Dynamic Therapy?
Photodynamic therapy uses a drug called a photosensitizing agent and a specific type of light. When the sensitizing agent is exposed to the particular wavelength of light, it produces oxygen that kills cancer cells in the vicinity. Doctors use photosensitizers and light of different wavelengths to treat cancers in various parts of the body.
Sonodynamic therapy uses a combination of a sonosensitizing agent and ultrasound to achieve the same objective, i.e., directly kill cancer cells and shrink a tumor by damaging blood vessels and activating the immune system.1 The energy source used in sonodynamic therapy to activate the sensitizer is sound (as opposed to light in photodynamic therapy).3
How is Sono-Photo Dynamic Therapy used to treat cancer?
The first step in the treatment is the injection of a sensitizing agent into the blood. The agent is absorbed by all the cells but remains in cancer cells for a longer duration. One to three days after injection of the sensitizer, it is no longer present in healthy cells but remains in cancer cells. Light from a laser or other sources is then used to activate the sensitizing agent. In sonodynamic therapy, ultrasound is used to activate the sensitizing agent. The active form of the agent produces a type of oxygen (reactive oxygen species) that destroys cancer cells in the vicinity.1,3
The procedure is usually done on an outpatient basis and can be performed with other cancer treatments such as chemotherapy, radiation therapy, and surgery. The photosensitizing agent Photofrin (porfimer sodium) has been approved by the FDA for the treatment of certain types of lung cancer and esophageal cancer.1 Photofrin is also used as a sonosensitizer. Other agents are being investigated as well.3 Sono-photodynamic therapy is a combination treatment that uses a sensitizer that can be activated by both light and sound.3
The limitation of Sono-Photodynamic therapy is that the light and sound needed to activate the sensitizing agent can only penetrate a limited thickness of tissue. For this reason, sono-photodynamic therapy is useful for tumors located under the skin or near body cavities. This treatment is less effective in large tumors which the light and sound cannot penetrate. It is also not recommended for metastatic tumors that have spread to other parts of the body.1
Does Sono-Photo Dynamic Therapy have any complications or side effects?
Healthy cells are usually unaffected by sono-photodynamic therapy because the photosensitizer remains only in cancer cells. Also, the light or sound is directed at the tumor, sparing normal tissue. However, there are some side effects of the treatment. The sensitizing agent porfimer sodium increases the sensitivity of the eyes and skin to light.1 For this reason, patients are asked to stay indoors and avoid sunlight for 6 weeks after sono-photodynamic therapy. The treatment can also lead to swelling, pain, burns, and scarring in healthy tissue.1 Other side effects of sono-photodynamic therapy include trouble swallowing, stomachache, shortness of breath, and discomfort with breathing.1