Development of an alternative light source to lasers for photodynamic therapy: 1. Comparative in vitro dose response characteristics

The relative performances of a prototype lamp, a pulsed laser and a continous wave laser, were compared for photodynamic therapy (PDT). Recent advances in short are technology and lamp miniaturization coupled with improvements in the effciency, of optical filter coatings have led to the design and construction of a table-top light source prototype; the first viable and cost-effective alternative to a laser, particularly in the field of PDT. The device can deliver over 1 W directly or 0.5W via a light guide within a 30 nm band centred at any wavelength from the ultra-violet to the near infra-red at fluence rates of over 1 W cm−2, in excess of that required for PDT. Its relative biological effectiveness (RBE), in vitro, has been proven alongside two PDT laser systems, an argon pumped dye laser and a copper vapour pumped dye laser.These first in vitro tests showed an efficiency of haematoporphyrin derivative, (HPD) induced cellular photoinactivation close to that of the argon/dye laser (RBE 100%), with a mean RBE for the lamp of 87±3% (p<0.05). The lamp proved to be superior, to that of the copper/dye laser system with an RBE of up to 150% at fluence rates above 50 m W cm−2. Transient photobleaching of the photosensitizer was the probable cause for the relative ineffectiveness of the copper/dye laser for PDT at high fluence rates.