Pulsed versus continuous wave excitation mechanisms in photodynamic therapy of differently graded squamous cell carcinomas in tumor-implanted nude mice.

The effectiveness of photodynamic therapy (PDT) in vivo was compared between the pulsed excimer laser-pumped dye laser system (EDL) and the continuous wave (cw) argon laser-pumped dye laser system (ADL). Serial subcutaneous transplantation was used to implant thymus aplastic nude mice with different grades of malignancy of two human squamous cell carcinomas (SCCs). Forty-eight hours after i.v. injections of a hematoporphyrin derivative (Photosan 3), the animals were irradiated with either pulsed-EDL or cw-ADL laser light at a tumor depth of 4-5 mm. The irradiation data were chosen as follows: EDL and ADL wavelength 630 nm, total dose 150 J/cm2, irradiation time 27.78 min; EDL repetition rate 30 Hz, single pulse energy 3 mJ, pulse width 20 ns; ADL intensity 90 mW/cm2. The effects of PDT were studied either by long-term observation of the animals treated or by evaluation of hematoxylin-eosin and Ki-67 histological sections of tumors 48 h after treatment. The EDL system proved to be at least as efficient as the ADL system as judged by the number of complete remissions. This became particularly evident in the treatment of the lower-graded tumors, with a good response observed in both transplanted SCCs. However, the higher-graded tumors showed a better response to PDT.