Determination of time-dependent protoporphyrin IX concentration for photodynamic therapy dosimetry in a mice colon tumor model using fluorescence spectroscopy.

Photodynamic therapy (PDT) is an effective treatment method for various types of invasive tumors. The efficiency of PDT treatment depends, to a great extent, on optimal dosimetry of light, the photosensitizer used, and on tissue oxygenation. Fluorescence spectroscopy can be employed for measurement of drug concentration in target tissue and can provide a basis for in vivo evaluation of treatment efficiency. We have developed an integrated system that can be used to determine photosensitizer concentration in vivo based on fluorescence measurements. In our study, we performed fluorescence measurements on colon tumors of Balb/c mice in which CT26 cells were injected subcutaneously in the right flank. 5-Aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) was used as the photosensitizer. ALA was administered intraperitoneally at a dose of 200 mg/kg and PpIX fluorescence profiles were followed up to 34 h after ALA administration. Maximum fluorescence intensity was found 8 h after ALA administration. Also, we determined the relationship between PpIX concentration in colon tumor tissue of Balb/c mice and its fluorescence intensity at the peak of the spectrum (635 nm). This was used to determine the PpIX content in the target tissue as a function of time after ALA administration.