Photodynamic Therapy - Advantages and Limitations

Advantages and Limitations

PDT is considered to be both minimally invasive and minimally toxic, these advantages alone make PDT an attractive alternative. Being a non-toxic therapy, PDT has become common in China because traditionally the country doesn't favour toxic therapies.

Compared to radiotherapy, chemotherapy and surgical operation for the treatment of cancers, PDT is in almost all cases a much cheaper alternative. Furthermore, post-operative recovery after PDT is typically hours or days rather than weeks.

Unlike chemotherapy for cancer the effect of PDT can be localised and specificity of treatment is achieved in three ways:

• First, light is delivered only to tissues that a physician wishes to treat. In the absence of light, there is no activation of the photosensitizer and no cell killing.
• Second, photosensitizers may be administered in ways that restrict their mobility.
• Finally, photosensitizers may be chosen which are selectively absorbed at a greater rate by targeted cells.

An important factor in the successful use of PDT is that light is needed to activate photosensitizers. This factor, more than any other, limited the development of PDT because most wavelengths of light can not penetrate through more than one third of an inch (1 cm) of tissue using standard laser technology and low powered LED technology. Thus, limiting application of PDT to the treatment of tumours on or under the skin, or on the lining of some internal organs. One way around this limitation is to use hollow needles to get the light into deeper tissues. Another way involves new high-powered LED technology to achieve much greater depth of light penetration. Also, the development of photosensitizers which are excited at 750–900 nm, wavelengths of light to which the body is relatively transparent (see Near-infrared window in biological tissue), can achieve a greater depth of light penetration of up to 5 inches.