Study objective: To look at the effect of interstitial
photodynamic therapy (PDT) in normal lung parenchyma to assess its
potential for treating localized, peripheral lung tumors.
Design: Studies were performed on normal Wistar rats using
the photosensitizer meso-tetrahydroxyphenyl chlorine. Drug distribution
was measured by fluorescence microscopy on tissue sections. Light was
delivered to the lungs via a single fiber inserted percutaneously under
x-ray control and the PDT effect studied in animals killed at times up
to 6 months later.
Results: Fluorescence studies
showed that the drug was initially distributed throughout the lung, but
was later predominantly in the vasculature, bronchi, and macrophages.
PDT produced sharply defined zones of hemorrhagic necrosis up to 12 mm
in diameter that healed with regeneration of bronchial epithelium and
local fibrosis. Different histologic effects were seen between drug
light intervals of 1 and 3 days. Treatment was well tolerated, there
was a low incidence of pneumothorax, and as long as the fiber tip was
within the lung parenchyma, there was no damage to adjacent
Conclusion: Interstitial PDT produces zones
of necrosis in normal lung that heal safely by a percutaneous technique
without affecting adjacent areas of untreated lung. If the lesion size
can be increased by using multiple fibers, this could be a promising
new technique for treating localized, peripheral lung cancers in
patients who are unfit for surgery.
Abbreviations: CCD = charge coupled
device; H & E = hematoxylin-eosin; mTHPC = meso-tetrahydorxyphenyl
chlorin; PDT = photodynamic therapy