Photo Dynamic Therapy (PDT)
Photo Dynamic Therapy (PDT), sometimes called photochemotherapy, is a form of phototherapy using nontoxic light-sensitive compounds that are exposed selectively to light. When photosensitizers are exposed to a specific wavelength of light, they produce a form of oxygen known as Reactive Oxygen Species (ROS), which is able to destroy resident cells through natural cell death, known as apoptosis.
Each photosensitizer is activated by light of a specific wavelength. This wavelength determines how far the light can travel into the body.
The laser light used in PDT can be directed through a fiber-optic (a very thin glass strand). The fiber-optic is placed close to the cancer to deliver the proper amount of light. The fiber-optic can be directed through a bronchoscope into the lungs for the treatment of lung cancer or through an endoscope into the esophagus for the treatment of esophageal cancer.
Benefits of PDT
An advantage of PDT is that it causes minimal damage to healthy tissue. However, because the laser light currently in use cannot pass through more than about 3 centimeters of tissue (a little more than one and an eighth inch), PDT is mainly used to treat tumors on or just under the skin or on the lining of internal organs.
The abnormal blood vessels in the wet form of macular degeneration are traditionally treated with laser. The thermal energy of the laser destroys both the blood vessels as well as the surrounding tissue (retina). Unfortunately, the majority of patients with wet macular degeneration have abnormal blood vessels located beneath the center of vision. Thus, laser treatment will destroy the center of vision- the very thing we want to protect. Photodynamic therapy could allow selective destruction of abnormal blood vessels without damage to surrounding tissues. The PDT dye is selectively absorbed by the abnormally proliferating blood vessels. When exposed to low levels of light ("non-thermal") the dye is activated and the abnormal blood vessels are selectively destroyed. PDT therapy is currently being evaluated in clinical trials. Two drugs are being evaluated: verteporfin (Vysudine) from CIBA vision and tin ethyl etiopurpurin (SnET2) from Miravant. Initial results are promising and have shown at least temporary recovery or preservation of vision in some patients. FDA approval of the PDT trials await completion of these studies to assess the overall safety and efficacy of these new agents.
It has no long-term side effects when used properly
It’s less invasive than surgery
It usually takes only a short time and is most often done as an outpatient
It can be targeted very precise
Unlike radiation, PDT can be repeated many times at the same site if needed
There’s little or no scarring after the site heals
It often costs less than other cancer treatments
Applications of PDT
PDT is used to treat cancers of the skin or those that are on, or near, the lining of internal organs. It can be used to treat cancers in the skin, the head and neck area, the lining of the mouth, the lining of the lung, the lining of the gullet (esophagus), the lining of the stomach and the lining of the bladder.
Nonmelanoma skin cancer and its precursors
Palliation of metastatic breast cancer to skin
Macular degeneration of the retina
Immunologic and inflammatory disorders
Cutaneous T cell lymphoma
Anal and vulva carcinoma
Neoplasias other than skin cancer
The ability of this treatment to hone in on dysplastic epithelial and endothelial cells while retaining viability of surrounding tissue is its key feature because this leads to specific tumor destruction with cosmesis and function of the target organ intact.