Photodynamic therapy or PDT is a treatment in which patients are given a drug that becomes activated under a specific wavelength of light, reacting with oxygen in the body to emit free radicals, which act as molecular bullets, killing surrounding cells and tissues. Various forms of PDT have been used successfully to treat a diverse range of cancers, as well as several benign diseases.
Drug Targeting
For PDT to be maximally effective and induce minimal side effects, the light reactive drug needs to be targeted to abnormal or cancerous tissues. Skin administration is sometimes the preferred route if the target tissue is superficial. Doctors administering PDT often make use of the body's capacity to concentrate drugs in specific organs or tissues. For example, aminolaevulinic acid is concentrated in mucosal membranes, and is therefore used in PDT for patients with abnormal cells in these regions, according to a June 2005 article published in "Technology in Cancer Research and Treatment."
Light Sensitivity
Longer wavelengths of light such as red light penetrate further into the body than blue light, which is a shorter wavelength. For this reason, blue light sensitive PDT drugs are less effective for treatment of abnormal cells deep within the body. Surgeons can circumvent this problem in some cases by making a surgical insertion and inserting a tool that contains a camera and emits a specific wavelength of light proximal to the target tissue, according to an August 2008 article published in "Technology in Cancer Research and Treatment."
Advantages
The main advantage of PDT is that treatment can be highly localized, because light is focused upon the target tissue, leading to a rapid drug reaction that only kills the targeted cells. Many techniques including some types of chemotherapy and surgery cause damage to collagen and elastin proteins which make up connective tissue, leading to scarring. Most PDT techniques do not affect these molecules, reducing the chance of scarring considerably, according to Macmillan Cancer Support.
Limitations
Coordinating PDT can be a complex and difficult task, because the direction and depth of tissue penetration by the light needs to be precise. Target tissues need to carry a lot of oxygen, because the activity of PDT drugs is dependent on this molecule. Many tumors have low levels of oxygen, due to a weak blood supply, rendering these tissues less suitable for PDT, according to a July 2008 article published in "Medical Research Reviews."
Side Effects
The type of drug, site of treatment and time between drug administration and light targeting leads to a range of variable side effects for these different types of PDT. A common side effect for many forms of PDT is skin light sensitivity following drug administration, according to a June 2005 article published in "Technology in Cancer Research and Treatment."
References
- "Technology in Cancer Research and Treatment"; A Review of Progress in Clinical Photodynamic Therapy; Z. Huang; June 2005
- "Technology in Cancer Research and Treatment"; Photodynamic Therapy for Treatment of Solid Tumors-Potential and Technical Challenges; Z. Huang, et al.; June 2008
- Macmillan Cancer Support: Photodynamic Therapy (PDT)
- "Medical Research Reviews"; Combination of Photodynamic Therapy and Immunomodulation: Current Status and Future Trends; Y. Quiang, et al.; July 2008
