Timing of illumination is essential for effective and safe photodynamic therapy: a study in the normal rat oesophagus

Br J Cancer. 1999 Feb;79(5-6):825-30. doi: 10.1038/sj.bjc.6690132.


5-Aminolaevulinic acid (ALA)-induced, protoporphyrin IX (PpIX)-mediated photodynamic therapy (PDT) is an experimental treatment modality for (pre)malignant oesophageal lesions. This study aimed to optimize the time of illumination after ALA administration. Six groups of eight rats received 200 mg kg(-1) ALA orally, eight rats served as controls. Illumination was performed at 1, 2, 3, 4, 6 or 12 h after ALA administration with a 1-cm cylindrical diffuser placed in a balloon catheter (laser parameters: 633 nm, 25 J radiant energy, power output 100 mW). During illumination, fluorescence measurements and light dosimetry were performed. Animals were sacrificed at 48 h (n = 4) or 28 days (n = 4) after PDT. At day 28, an oesophagogram was performed. Largest PpIX fluorescence was found at 3 h after ALA administration. In vivo fluence rate was three times higher than the calculated incident fluence rate. At 48 h after PDT, major epithelial damage was found in all animals illuminated at 2 h, whereas less epithelial damage was found at 3-6 h and none at 1 and 12 h. In animals illuminated at 4, 6 and 12 h, but not at 2 h, oesophagograms showed severe dilatations and histology showed loss of Schwann cells. These results demonstrate that the choice of time interval between ALA administration and illumination is critical for achieving epithelial damage without oesophageal functional impairment. A short interval of 2-3 h seems to be most appropriate.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminolevulinic Acid / toxicity*
  • Animals
  • Edema
  • Esophagus / drug effects*
  • Esophagus / pathology
  • Esophagus / radiation effects
  • Light / adverse effects
  • Male
  • Mucous Membrane / drug effects
  • Mucous Membrane / pathology
  • Mucous Membrane / radiation effects
  • Muscle, Smooth / drug effects
  • Muscle, Smooth / pathology
  • Muscle, Smooth / radiation effects
  • Photochemotherapy / adverse effects
  • Photochemotherapy / methods*
  • Photosensitizing Agents / toxicity*
  • Protoporphyrins / toxicity*
  • Rats
  • Rats, Wistar
  • Spectrometry, Fluorescence
  • Time Factors


  • Photosensitizing Agents
  • Protoporphyrins
  • Aminolevulinic Acid
  • protoporphyrin IX