title: Photodynamic therapy of Walker tumors by multiple laser irradiation.
abstract: OBJECTIVE
  Photodynamic therapy of Walker tumor after subcutaneous administration of 5-ALA solution using a multiple laser irradiation scheme was monitored by the fluorescence imaging technique to investigate the effectiveness of 5-ALA-PDT.
  
  
  BACKGROUND
  Photodynamic therapy (PDT) is a localized cancer treatment based on the selective uptake and retention of photosensitizer at the tumoral level and on the activation of the photosensitizer by a specific wavelength of light, aiming to induce cytotoxic reactions. As a new photosensitizer, the heme precursor 5- aminolevulinic acid has been introduced recently for photodynamic therapy of tumors and precancerous lesions of the skin. It has been shown that the efficacy of topical 5-ALA-PDT is limited for deeper skin tumor by the depth of 5-ALA penetration through the skin. Oral or systemic administration of ALA or the use of different irradiation schemes may improve tumor response to PDT.
  
  
  METHODS
  Laser irradiation parameters used in this study were lambda = 635 nm, P = 3 mW, t(exp) = 300 sec, and three sessions. The fluorescence was excitated by monochromatic light of 405 nm. The temporal behavior of PpIX fluorescence was studied by processing and analyzing the fluorescence images acquired just after applying 5-ALA, just before and just after three laser irradiations.
  
  
  RESULTS
  The results demonstrate that PpIX is highly selective for tumors areas and a re-accumulation of PpIX appears between laser irradiations. During laser irradiation, the PpIX fluorescence intensity decreases rapidly, reflecting the photodegradation of PpIX.
  
  
  CONCLUSIONS
  In conclusion, the use of a multiple laser irradiation scheme, for the activation of reaccumulation of Pp IX (with three steps) is effective for photodynamic therapy of Walker tumor.
authors.affiliation: National Institute for Optoelectronics, Bucharest, Romania.
authors.forename: Mihaela Antonina
authors.initials: MA
authors.lastname: Calin
authors.forename: Maria Iuliana
authors.initials: MI
authors.lastname: Gruia
authors.forename: Nicoleta
authors.initials: N
authors.lastname: Herascu
authors.forename: Toma
authors.initials: T
authors.lastname: Coman
mesh_terms: D000622:Aminolevulinic Acid / Q000494:pharmacology*; D000818:Animals; D002279:Carcinoma 256, Walker / Q000188:drug therapy* / Q000503:physiopathology / Q000532:radiotherapy; D009368:Neoplasm Transplantation; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011524:Protoporphyrins / Q000502:physiology* / Q000528:radiation effects; D051381:Rats
chemical_list: D017319:Photosensitizing Agents; D011524:Protoporphyrins; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX