Predicting the therapeutic outcome of photodynamic therapy (PDT) requires knowledge of the changes in photosensitizer concentration during the treatment. To investigate this, in vitro experiments were performed in which CT26 cells derivated from colon carcinoma tumor of BALB/c mice were injected subcutaneously in the right flank of mice. 5-aminolaevulinic acid is injected intraperitoneally at a dose of 500 mg kg-1, and the fluorescence intensity in each tissue sample excised from tumor was measured with a spectrofluorometer at 2 and 3 hour after administration. Maximum fluorescence intensity of the tissue homogenates was detected at 600 nm. Results yield the possibility to determine the variation of induced PpIX in tumor by measuring fluorescence intensity and based on standard curve, which is useful for dosimetry in photodynamic therapy.

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