Comparison of continuous and fractionated illumination during hexaminolaevulinate-photodynamic therapy

Objective: This experimental study aimed to compare continuous and fractionated illumination to optimize hexaminolaevulinate (HAL)-photodynamic therapy (PDT) in a rat tumour model with advanced ovarian cancer. Materials and methods: Intraperitoneal 10(6) NuTu-19 cells were injected in 36 female rats Fisher 344. Peritoneal carcinomatosis was obtained 26 days post-tumour induction. Four hours post-intraperitoneal HAL (Photocure ASA, Osto, Norway) injection, two schemes of PDT were performed at 30 mW cm(-2) on a 1 cm(2) area: fractionated illumination (n = 16) with a on-off cycle ("on": 2 min and "off": 1 min) until a fluence of 30 J cm(-2) was delivered, and continuous illumination (n = 20) with a fluence of 45 J cm-2. Laser light was generated using a 532 nm KTP laser (Laser Quantum, Stockport, UK). Biopsies were taken 24h after treatment. Semi-quantitative histology was performed. Necrosis vatue was determined-0: no necrosis to 4: full necrosis. Results: HAL-PDT was efficient in producing necrosis irrespective of the scheme (NV = 3.34 +/- 0.91). Tumour destruction was superior with fractionated illumination compared to continuous illumination (3.67 +/- 0.70 vs. 3.10 +/- 0.94) (p < 0.05). Conclusion: Fractionated illumination during photodynamic therapy was shown to improve tumour response. Fractionated illumination with short intervals should be considered for an effective PDT of advanced ovarian cancer. (C) 2008 Elsevier B.V. All rights reserved.