Tissue heterogeneities as well as distinct metabolic status and cellular types within a tumor may results in a nonhomogenous
necrosis. The possibility of PDT surviving cells within a treated volume has relevant clinical significance.
The major aim of this study was to analyze, on normal rat liver, the cell viability and surviving after PDT. The porphyrin
was injected through the cava vein at concentration of 1.5 mg/Kg. The induced necrosis was qualitatively investigated
varying the used drug light interval (30 min, 1, 3, 6, 24 and 36 h) and total delivered dose (20, 50, 100, 150 and 200
J/cm2). A diode laser at 630 nm and irradiance of 150 mW/cm2 was employed. The exposed livers were removed after
the animals were killed by anesthesia overdose, 30 h after illumination. Slides were processed by HE analysis for the
determination of the overall aspects of the necrotic and non-treated liver. We observed necrosis of central vein and
presence of surviving cell around the portal triad within the necrotic volume, suggesting PDT-resistant regions of the
tissue. Possible hypothesis for the observation may be: the absence of photosensitizer; insufficient light dose (below
threshold); and distinct metabolic status in the portal triad microregions decreases oxygen availability to photodynamic
reaction. The cells surrounding portal triad presented a higher resistance even when 200 J/cm2 was applied. In contrast,
the cells closer to the central vein after 20 J/cm2 were already susceptible to the action of PDT. Different aspects of the
problem are presented.