Singlet Oxygen (1O2) Luminescence Dosimetry (SOLD) and fluorescence photobleaching are being investigated
as dosimetric tools for clinical PDT. Both have been applied during superficial ALA-PDT of normal skin and
skin cancers. The interpretation of fluorescence and SOLD data is complicated by the non-uniform distribution
and bleaching of PpIX and the absorption and scattering of light in the skin. The aim of the present work was
to tackle these challenges using Monte Carlo (MC) simulations. Skin was modeled as a three-layer semi-infinite
medium with uniform optical properties in each layer. The initial depth-dependent distribution of PpIX was an
exponential decay and, after the delivery of each treatment fluence increment, standard photochemical reaction
kinetics were used to update the distribution of sensitizer and reacted singlet oxygen. Oxygen depletion due to
photochemical consumption or vascular shutdown was also incorporated in the model. The adjoint method was
applied to calculate the PpIX fluorescence and 1270 nm singlet oxygen luminescence reaching the skin surface
in each time increment. The time-resolved evolution of the fluorescence and cumulative SOLD signals during
treatment were compared to the time-resolved volume-averaged distribution of reacted singlet oxygen in the
dermis layer for typical clinical PDT conditions. Approximate linear relationships were observed over most of
the treatment time.
Photodynamic therapy (PDT) can be targeted toward different subcellular localizations and it is widely believed different
subcellular targets vary in their sensitivity to photobiological damage. In this study, PDT-generated near-infrared singlet
oxygen (1O2) luminescence was measured along with cell viability under two different incubation protocols: 5-
aminolevulinic acid (ALA) endogenously-induced protoporphyrin IX (PpIX) and exogenous PpIX, at different
incubation times. Confocal fluorescence microscopy indicated that ALA-induced PpIX (2 h) localized in the
mitochondria, whereas exogenous PpIX (1 h) mainly localized to the plasma membrane. Cell viability was determined at
several time points during PDT treatments using colony-forming assays, and the surviving fraction correlated well with
cumulative 1O2 luminescence counts under both incubation protocols. Preliminary results indicate the plasma membrane
is less sensitive to PDT-generated 1O2 than the mitochondria.
Bioluminescence Imaging (BLI) has been employed as an imaging modality to identify and characterize
fundamental processes related to cancer development and response at cellular and molecular levels. This
technique is based on the reaction of luciferin with oxygen in the presence of luciferase and ATP. A major
concern in this technique is that tumors are generally hypoxic, either constitutively and/or as a result of
treatment, therefore the oxygen available for the bioluminescence reaction could possibly be reduced to
limiting levels, and thus leading to underestimation of the actual number of luciferase-labeled cells during in
vivo procedures. In this report, we present the initial in vitro results of the oxygen dependence of the
bioluminescence signal in rat gliosarcoma 9L cells tagged with the luciferase gene (9Lluc cells).
Bioluminescence photon emission from cells exposed to different oxygen tensions was detected by a sensitive
CCD camera upon exposure to luciferin. The results showed that bioluminescence signal decreased at
administered pO2 levels below about 5%, falling by approximately 50% at 0.2% pO2. Additional experiments
showed that changes in BLI was due to the cell inability to maintain normal levels of ATP during the hypoxic
period reducing the ATP concentration to limiting levels for BLI.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.