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Also known as photoradiation, phototherapy, or photochemotherapy, it is used to treat certain types of cancer.
It is based on the discovery that certain chemicals known as photosensitizing agents that can kill organisms when exposed to a particular type of light.
Photodynamic therapy kills cancer cells by using a fixed frequency laser light (a narrow, intense beam of light) in combination with a photosensitizing agent.
Photodynamic therapy is a treatment for various skin conditions .
Phototherapy requires a combination of a drug and the application of energy to create a chemical reaction that targets certain growths or skin conditions.
The drug is generally applied in a cream formulation and the energy is obtained from a strong light source.
Uses of photodynamic therapy
Photodynamic therapy is most often used to treat superficial skin cancers and solar keratoses ( sun spots ).
For skin cancers, a biopsy done in advance will usually have confirmed the diagnosis.
Photodynamic therapy is performed to treat:
- Skin cancer.
- Head and neck cancer.
- Gastrointestinal cancer, such as stomach cancer and gastrointestinal stromal tumors.
- Lung cancer.
Process
- The photosensitizing agent is injected into the bloodstream and absorbed by cells throughout the body. This agent stays in cancer cells longer than it does in normal cells.
- Cancer cells when treated are exposed to lasers and the photosensitizing agent produces an active form of oxygen, which kills cancer cells.
- The laser light used can be directed through an optical fiber (a very thin glass filament). Fiber optics are placed close to where the cancer is to deliver the right amount of light. Fiber optics 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.
- Exposure of the area requiring treatment to light must be carefully measured to occur when most of the photosensitizing agent has left the healthy cells, but is still present in the cancer cells.
Photodynamic therapy causes minimal damage to healthy tissue. However, because the laser light currently in use cannot pass through more than three centimeters of tissue (a little more than one and one-eighth of an inch).
It is used primarily to treat tumors on or just under the skin or on the inner lining of organs.
Photodynamic therapy offers patients a non-invasive cancer treatment option.
There is no pain during the procedure (although some patients with physical limitations may experience some discomfort when placed).
At the beginning of each session, the radiation therapist will place the treatment on the patient and set up the equipment according to the radiation oncologist’s instructions.
X-rays are taken to ensure the patient is in the proper treatment position. Once the patient is in position, the therapist will enter the adjoining control room.
From here, the patient is monitored during treatment on a television screen and via voice communication.
If the patient has any concerns, or feels ill or uncomfortable, this can be expressed to the radiation therapist using the microphone located in the treatment room.
Depending on the circumstances of the individual patient, a course of radiation therapy is usually conducted five days a week for several weeks.
Generally, it is done for about an hour each day, with an actual radiation therapy session lasting 15 to 30 minutes.
Patients are seen at least once a week by a radiation oncologist. During this appointment, the radiation oncologist assesses the patient’s response to treatment.
As needed, the amount of radiation delivered to the patient will be modified based on the radiation oncologist’s observations.
Blood tests and X-rays may also be ordered, to see how the patient’s body responds to treatment. If the tumor shrinks significantly, another application may be necessary.
This allows adjustments to the treatment to be made so that the treatment destroys the rest of the tumor and even more normal tissue is protected.
Photodynamic therapy in skin cancer
The common procedure for treating superficial skin cancer with photodynamic therapy is done by identifying and marking the lesion.
The surface is gently scraped to remove any scab present on the lesion. This is sometimes mildly painful and may even bleed.
Next, a special cream is applied to the lesion, after which it is covered with a dressing. Additional padding can be applied to ensure the bandage is opaque. This is left intact for three hours.
The bandage is removed and any residual cream from the injury is wiped off. A bright light source is then irradiated onto the lesion, which is kept 5 to 8 centimeters away from the skin for approximately 8 minutes.
The light is very bright and goggles should be worn. Subsequently, the lesion is cleaned and the dressing is placed again.
The dressing must be kept intact for at least 24 hours and the area of the injury protected from the incidence of sunlight.
Treatment for skin cancers is usually repeated again in one to three weeks.
Photodynamic therapy in the bronchi
There are several methods available to help destroy endobronchial (airway) cancers.
Photodynamic therapy is a unique form of airway treatment that uses light energy to activate a systemic drug delivered directly to the area.
A medicine called porfimer sodium is given by injection into a vein and laser light energy is applied to the airways two to three days later.
A chemical reaction occurs that causes the destruction of tumor cells that have absorbed the drug.
In a similar way, we proceed in the application of photodynamic therapy in the gastrointestinal system.
Contraindications
Photodynamic therapy is suitable only for certain skin conditions.
In regards to skin cancers, photodynamic therapy has been shown to provide an acceptable cure rate only for skin cancers, not for superficial melanoma.
People with strong sensitivity to light or photosensitive disorders such as lupus may not be suitable candidates for this form of treatment.
People suffering from claustrophobia may find dressings and close application of strong light difficult to bear.
Skin redness and scabbing develop after treatment and will require simple cleanings and dressing.
Side effects during the application of photodynamic therapy
During treatment, discomfort at the treatment site is very common. This can include burning, stinging, or tenderness.
Cold air blowing on the skin can ease discomfort. Treatment can be stopped if necessary to provide pain relief, such as a local anesthetic.
The discomfort usually ceases quickly when the light is turned off but can occasionally persist.
Some redness, swelling, and crusting of the skin is expected after the procedure, but will usually disappear after a few days.
Occasionally, there may be more severe swelling, blisters, or itching. In some cases, the skin may become lighter or darker.
Increased skin color usually fades over months, but decreased skin color can be permanent at times.
Rare side effects have been reported including anxiety, headaches, dizziness, migraines, thinning of the skin, widespread skin rashes, abnormal tear production, nausea, tiredness, flu-like symptoms, and skin infections.
Follow-up
Follow-up should be done with the dermatologist.
The treated area should be checked within a few weeks to ensure that the area is healing properly and that there is no residual or recurring long-term concern.
Regular check-ups are recommended to ensure that any new skin lesions are detected and treated.
