INTRAPERITONEAL PHOTODYNAMIC THERAPY - COMPARISON OF RED AND GREEN LIGHT-DISTRIBUTION AND TOXICITY

The aim of this study was to compare red (652 nm) and green (514 nm) l ight for photodynamic therapy (PDT) of the peritoneal cavity with emph asis on light distribution and toxicity. Red-Light PDT was limited by intestinal toxicity and it was hypothesized that less penetrating gree n light would allow higher light doses to be used in the peritoneal ca vity, Female non-tumor-bearing rats were photosensitized with mTHPC (m eta-tetrahydroxyphenylchlorin, Foscan(R)) intravenously or intraperito neally and the peritoneum was illuminated using a minimally invasive t echnique. For both red and green Light, the time of illumination was v aried to give the required dose, Light fluence rate was measured in si tu at multiple sites within the abdominal cavity. The toxicity experim ents were carried out with a total of 160 J incident red or 640 J inci dent green light and a drug dose of 0.15 mg/kg Foscan(R), For red ligh t a mean fluence rate of 55.2 +/- 38.5 mW cm(-2) was measured, with a peak fluence rate of 128 mW cm(-2) on the intestines. For green Light the mean and peak fluence rates were 8.2 +/- 9.0 (i.e, including zero fluence rate measurements) and 28 mW cm(-2), respectively, Intestines were most vulnerable to red light illumination. The intravenous inject ion route resulted in increased toxicity for red light, but for green light there were no major differences between intravenous and intraper itoneal routes, The 4 h interval between drug and illumination resulte d in very little toxicity for both wavelengths, We conclude that for i ntraperitoneal PDT green light allows higher light doses than red ligh t, but the light distribution over the peritoneum is much less favorab le and may not be suitable for whole peritoneal illumination using a m inimal-access technique.