slides
In Vivo Monitoring of Photodynamic Therapy: from lab to clinic
- Publication date
- 15 January 2010
- Publisher
- Photodynamic therapy (PDT) is an emerging clinical treatment modality, which utilizes
light, oxygen and a light sensitive drug (the photosensitizer), for curative and palliative
treatment of a variety of malignant and non-malignant conditions tumors. PDT is
frequently used in the clinic for treatment of superficial skin lesions by superficial
illumination of the lesion after the topical administration of a photosensitizer or its precursor.
However, PDT is also under investigation for treatment of larger tumors
volumes in regions such as the head and neck1,2 and the prostate3 by inserting opticfibers
in the tumor volume for the delivery of the treatment light.
The therapeutic effect in PDT is induced by the interaction between the tissue and
reactive oxygen radicals. These reactive oxygen radicals, predominantly singlet
oxygen, are formed by the interaction of photosensitizer, light (of an appropriate
wavelength) and oxygen in the tissue. The deposited PDT dose is the amount of light
that actually interacts with the photosensitizer that leads to formation of reactive
oxygen species responsible for inducing tissue response. Note that this is different
from the actual amount of light delivered to the tissue since not all of the light delivered
interacts with the photosensitizer scattering and absorption of the tissue. In addition,
based on the photosensitizer’s ability to form reactive oxygen species (ROS) only a
percentage of light that interacts with the photosensitizer lead to formation of ROS.
Also there is a difference between the actual delivered light dose and the intended
delivered light dose. Where the intended delivered light dose is set by the clinician to
be delivered. Only by measuring the amount of light in situ it is possible to determine
the actual delivered light dose. So although this intended light dose is kept the same in
individuals undergoing treatment, the actual delivered light dose and the deposited
PDT dose can vary due to biological variation and the dynamic interaction between
light, photosensitizer and oxygen in tissue. Inter individual variations in deposited PDTdose
yield variations in induced tissue response and treatment outcome. For this
reason it is necessary to determine and monitor the deposited PDT dose during
therapeutic illumination.