According to the Centers for Disease Control and Prevention (CDC), lung cancer is the third most common cancer in the United States. And, because the lungs can’t be seen or felt, detecting and treating the disease can prove extremely challenging. Thankfully there is hope with photodynamic therapy. Abhishek Biswas, MD, FACP, PPG – Pulmonology, answers our questions and helps explain how specialists with PPG – Pulmonary and Critical Care may utilize this innovative therapy to treat lung cancer and pulmonary lung diseases.
What is photodynamic therapy?
Photodynamic therapy (PDT) is a two-stage treatment that combines light energy with a drug (photosensitizer) designed to destroy cancerous and precancerous cells after controlled light activation. Photosensitizers are chemicals that are activated by a specific wavelength of light energy, usually from a laser. The photosensitizer is nontoxic until activated by light. However, after light activation, the photosensitizer becomes toxic to the targeted tissue. [1] Parkview’s interventional pulmonologists utilize this treatment by shining light energy on cancerous tissue through a bronchoscopy, causing inflammation within the diseased tissue and death of the cancer cells.
How does photodynamic therapy work?
PDT with a photosensitizer is a two-step process. The first step requires an injection of the drug. It is administered as a single slow intravenous injection over 3-5 minutes on the first day. Step two involves exposing any cancerous tissue to the laser light application, which usually occurs on the third day. Light energy at a specific wavelength then activates the drug to an excited state. This 48-hour process allows selective retention of the photosensitizer within the tumor and clearance from other organs.
Further transfer of this energy to surrounding cancer tissue causes reactive cell destruction. The activated photosensitizer agent also induces vasoconstriction and vascular obstruction, causing tumor cells to die. Continual cell death continues for a few days after exposure to light therapy, which is why the effects of this treatment occur over a few days after light exposure.
What conditions, illnesses or diseases does this type of therapy treat?
While photodynamic therapy is used to treat a variety of conditions, the following diseases benefit from this form of treatment:
- Early-stage central airway lung cancer (helping avoid the need for extensive surgery or radiation)
- Restoration of obstructed airways due to advanced lung cancer (providing symptomatic relief)
What are some of the advantages of PDT?
A significant advantage of PDT therapy stems from the deeper penetration of energy through the bronchus wall compared to other modalities. The anti-tumor effect of PDT persists for days after applying light, whereas other modalities like laser or electrothermal energy have immediate but short-lived results.
What are some of the limitations of PDT?
PDT is utilized only in cases where light energy is accurately applied. Some cancers may not be amenable to this therapy due to their location. Additionally, this is a slow modality, so it takes a few days to take effect. Therefore, this treatment may not be helpful for severely symptomatic patients who need urgent interventions to open their obstructed airways.
What can someone expect after the procedure?
Most patients can expect some coughing following the procedure, which usually settles down in a few days. However, patients will remain photosensitive for several weeks and must protect themselves from bright light until the photosensitizing agent gets expelled from their bodies. This process can take between 3-4 weeks to complete. We provide our patients with gloves, sunglasses and wide-brimmed hats to protect them throughout this period.
How does PDT compare to other modalities or forms of therapy within the field?
In some cases, PDT may allow us to avoid surgery for certain early-stage lung cancers. And, while surgery remains the treatment of choice for all operable lung cancers, PDT helps open another avenue for treatment for those with compromised lung functions and may not have been a candidate in the past.
References
[1] Mayo Clinic
