Razi Journal of Medical Sciences

    Background: The important issue in the application of Photodynamic Therapy (PDT), as one of the fundamental basis of new treatment for cancerous lesions, is optimal dosimetry. In this context, it is necessary to obtain enough information about the drug concentration within the target tissue. On the other hand, the fact that

ALA itself is not a photosensitizer and causes the production of Protoporphyrin IX (PpIX) in target tissue, determining the amount of PpIX produced in the target tissue is important for PDT dosimetry. Thus, in this study fluorometry and fluorescence spectroscopy have been investigated to determine the concentration of PpIX within the target tissue.

Methods: This study was carried out in vivo on CT26 cell line of Balb/c mouse. In this context, first by subcutaneous injection of 10⁶ CT26 cells into right side of 18 Balb/c mice (6-8 weeks old, weighting 20-28 gr), colon carcinoma tumors were induced. Then, tissue concentration of PpIX was determined by using two methods: fluorometry and fluorescence spectroscopy. Statistical analysis of data, after ensuring normal distribution of data in the 95% confidence, was conducted using student’s t-test in SPSS V.12 software.

Results: Based on the results, appropriate PpIX fluorescence excitation wavelength is 407 nm. Also, 8 hours after injection of

ALA, PpIX accumulation reaches its maximum and then the process of drug discharge begins. Thus if there is no problem to keep the patient in the dark room, the best time for radiation of treatment laser is 8 hours after ALA injection. On the other hand, in both methods by measuring the fluorescence spectrum of tissue and based on the standard curve determined for PpIX, the concentration of PpIX within the tumor tissue was determined.

Conclusion: Considering the importance of determining the amount of drug accumulated within the tissue, both in clinical applications of PDT and modeling of PDT dosimetry which is a step in order to optimize this therapy, both methods fluorometry and fluorescence spectroscopy are effective. However fluorescence spectroscopy, as being noninvasive and allowing real time measurement, is preferd to fluorometry.