Monitoring of photobleaching in photodynamic therapy using fluorescence spectroscopy

Photodynamic therapy (PDT) utilizing aminolevulinic acid (ALA) as a photosensitiser has been used to ablate premalignant/malignant skin conditions including superficial basal cell carcinoma (BCC) with acceptable cosmetic outcome. Clinicians continue however to face difficulties in determining the exact dose that is sufficient to achieve a complete healing from the condition where the experience of the clinician remains the only determinant factor. This inaccuracy sometimes leads to undertreating these lesions. Here, we have clinically evaluated the use of fluorescence imaging system as monitor of protoporphyrin IX (PpIX) photobleaching in patients with BCC and compares this to the clinical outcome. Four readings were acquired from each patient (n=14) "pre-PDT", "peri-PDT" (333secs), "peri-PDT" (660secs) and post-PDT. It was found that red fluorescence values decreased markedly during PDT, and considered to be significant when compared to pre-PDT (P = 0.0018) and post- PDT (P = 0.0025). The red fluorescence value in pre-PDT was found to be higher in BCC of cheek and scalp (where the response rate, RR = 100%) in comparison to the temple (RR = 75%) and nose (RR = 33%). By comparison, the post- PDT red fluorescence values in cheek and scalp were lower than that of the temple and nose, respectively; this may be a useful indicative of the response rate of tissue to therapy.