Fluorescence imaging for photodynamic therapy of non-melanoma skin malignancies – A retrospective clinical study

Abstract

Background and objective: Photodynamic therapy (PDT) has been successfully used in clinical practice for decades; however, clinical outcome data are not always consistent resulting in a great necessity for real-time monitoring to predict the therapy outcome. Study design and methods: In a retrospective clinical study, 402 patients with non-melanoma skin malignancies were enrolled who underwent PDT treatment and fluorescence real-time imaging. The photosensitizer used was a chlorine e6 derivative (Fotoditazin^®); the tumors were irradiated with a 662 nm continuous wave diode laser with fiber delivery system and total fluence of up to 300 J/cm². The fluorescence imaging was performed using a commercially available system with a camera and bandpass filter in the range of 710–800 nm. Fluorescence contrast (FC) of the tumor (the ratio of the average fluorescence intensities in the tumor and the surrounding tissues) and its change during the PDT treatment (photobleaching, dFC) was measured. Then the correlation between the clinical outcome (tumor response and recurrence rate) and measured fluorescence parameters was evaluated. The follow-up period was 6–53 months (median, 28 months). Results: FC or dFC below their median values independently correspond to a significant increase in tumor recurrence rate (pFC, and not correlated with the photobleaching. Conclusion: Baseline FC and its change after PDT treatment may serve as a predictor of recurrence. This finding is a step towards individualized PDT cancer treatment.