title: Monte Carlo modeling of in vivo protoporphyrin IX fluorescence and singlet oxygen production during photodynamic therapy for patients presenting with superficial basal cell carcinomas.
abstract: We present protoporphyrin IX (PpIX) fluorescence measurements acquired from patients presenting with superficial basal cell carcinoma during photodynamic therapy (PDT) treatment, facilitating in vivo photobleaching to be monitored. Monte Carlo (MC) simulations, taking into account photobleaching, are performed on a three-dimensional cube grid, which represents the treatment geometry. Consequently, it is possible to determine the spatial and temporal changes to the origin of collected fluorescence and generated singlet oxygen. From our clinical results, an in vivo photobleaching dose constant, β of 5-aminolaevulinic acid-induced PpIX fluorescence is found to be 14 ± 1 J/cm(2). Results from our MC simulations suggest that an increase from our typical administered treatment light dose of 75-150 J/cm(2) could increase the effective PDT treatment initially achieved at a depth of 2.7-3.3 mm in the tumor, respectively. Moreover, this increase reduces the surface PpIX fluorescence from 0.00012 to 0.000003 of the maximum value recorded before treatment. The recommendation of administrating a larger light dose, which advocates an increase in the treatment time after surface PpIX fluorescence has diminished, remains valid for different sets of optical properties and therefore should have a beneficial outcome on the total treatment effect.
authors.affiliation: University of St. Andrews, School of Physics and Astronomy, North Haugh, St Andrews, Fife KY16 9SS, United Kingdom.
authors.forename: Ronan M
authors.initials: RM
authors.lastname: Valentine
authors.forename: C Tom A
authors.initials: CT
authors.lastname: Brown
authors.forename: Harry
authors.initials: H
authors.lastname: Moseley
authors.forename: Sally
authors.initials: S
authors.lastname: Ibbotson
authors.forename: Kenny
authors.initials: K
authors.lastname: Wood
mesh_terms: D000622:Aminolevulinic Acid / Q000493:pharmacokinetics / Q000494:pharmacology*; D002280:Basal Cell Carcinoma / Q000188:drug therapy* / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D038761:Photobleaching; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000032:analysis / Q000493:pharmacokinetics / Q000494:pharmacology; D011524:Protoporphyrins / Q000032:analysis* / Q000493:pharmacokinetics; D026082:Singlet Oxygen / Q000032:analysis* / Q000378:metabolism; D012878:Skin Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D017319:Photosensitizing Agents; D011524:Protoporphyrins; D026082:Singlet Oxygen; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX