  Background: Promising results for mammary carcinoma treatment with
photodynamic therapy (PDT) presuppose a careful selection of irradiation light
wavelength. Methods: 4T1 tumors implanted in NOD-SCID mice were treated with
Metvix-PDT under 625 nm, 660 nm and their combination light, for a fixed
radiant exposure. The therapeutic outcome was assessed through Monte Carlo
based computational simulations along with a preliminary in vivo study, where
fluorescence, size and temperature measurements were conducted. Results: The
light source combination protocol presents great potential, since it results in
high cytotoxic products levels and reduced treatment times; while the in vivo
findings, regarding the harvested tumor mass, also support this hypothesis. The
irradiation with 625 nm beam alone presented better results for most of the in
vivo measured parameters. The mouse treated with only the 660 nm light source
had the highest un-photobleached photosensitizer (PS) signal, the lowest body
temperature, the heaviest harvested tumor and the lowest estimated
concentration of PDT cytotoxic products. Conclusions: The use of 625 nm
irradiation light matches the PS excitation band but is preferable only for
treatment of superficial tumors. For deeper laying masses, the simultaneous use
of longer wavelengths enhances the therapeutic outcome due to their increased
penetration depth.
