Using white light during photodynamic therapy: visualization only or treatment?
BACKGROUND
Photodynamic therapy (PDT) involves selective uptake and retention of a photosensitizer in a tumor, followed by irradiation with light (usually a 630 nm diode laser), initiating tumor necrosis through formation of oxidized products or singlet oxygen. Successful PDT of early cancers of the esophagus and of Barrett's esophagus with severe dysplasia has been reported. However, side effects (edema, stricture, etc.) and treatment failure have been observed. This study aims to evaluate the possible photodynamic effect induced by illumination from the endoscope on the PDT effect, since a photon emitted to see the lesion can potentially be a photon to treat it!


METHODS
Two fiber endoscopes (Olympus GIFPQ20 and Pentax FG34X) and one videoendoscope (Olympus GIFQ140) were evaluated. Output power, irradiance and emission spectrum were measured. Using the molar extinction coefficient of Photofrin and optical coefficients of the esophagus, the relative photodynamic reaction yield, determined as a function of depth, was compared with that obtained with a 630 nm diode laser.


RESULTS
The irradiance at 1 and 2 cm was, respectively, 18.4 and 4.6 mW/cm (Pentax FG34X), 10.6 and 2.65 mW/cm (Olympus GIFPQ20), and 2.7 and 3.2 mW/cm (Olympus GIFQ140). The highest irradiance could lead to a relative photodynamic reaction yield at the surface of the esophagus similar to (Olympus GIFPQ20) or greater than (Pentax FG34X) that obtained using a diode laser alone.


CONCLUSIONS
Our results could explain side effects sometimes observed when performing PDT. 'Endoscopic' illumination, however, could also represent an interesting alternative to the 630 nm diode laser. When using white light, superficial efficacy of PDT could be reinforced and transmural necrosis leading to perforation or stenoses reduced, since there is less red light in depth compared with a diode laser.
Mordon
Serge
S
INSERM IFR 114 bDepartment of Gastroenterology, Lille University Hospital, Lille, France. mordon@lille.inserm.fr
Maunoury
Vincent
V
D000042:Absorption; D017323:Dihematoporphyrin Ether / Q000737:chemistry; D004938:Esophageal Neoplasms / Q000188:drug therapy / Q000628:therapy*; D020701:Esophagoscopes; D005336:Fiber Optic Technology; D006801:Humans; D008027:Light; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000737:chemistry; D010789:Phototherapy; D012542:Scattering, Radiation; D014741:Video Recording
D017319:Photosensitizing Agents; D017323:Dihematoporphyrin Ether