Protoporphyrin IX photobleaching during the light irradiation phase of standard dermatological methyl-aminolevulinate photodynamic therapy

• Published in: Photodiagnosis and photodynamic therapy Vol. 7; no. 4; pp. 232 - 238
• Main Authors: Tyrrell, Jessica, Campbell, Sandra, Curnow, Alison, PhD
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-12-2010
• Subjects: Aged; Aged, 80 and over; Aminolevulinic Acid - analogs & derivatives; Aminolevulinic Acid - therapeutic use; Female; Fluence; Fluorescence diagnosis; Hematology, Oncology and Palliative Medicine; Humans; Internal Medicine; Male; Methyl-aminolevulinate (MAL); Photobleaching; Photochemotherapy; Photodynamic therapy (PDT); Photosensitizing Agents - therapeutic use; Precancerous Conditions - drug therapy; Protoporphyrin IX (PpIX); Protoporphyrins - therapeutic use; Skin Neoplasms - drug therapy; Fluorescence diagnosis; Methyl-aminolevulinate (MAL); Fluence; Photodynamic therapy (PDT); Photobleaching; Protoporphyrin IX (PpIX)
• ISSN: 1572-1000; 1873-1597
• DOI: 10.1016/j.pdpdt.2010.09.005

Summary Background Methyl-aminolevulinate photodynamic therapy (MAL-PDT) is a successful treatment for non-melanoma skin cancers in the UK. Monitoring the photobleaching of the photosensitiser, protoporphyrin IX (PpIX) during treatment has been demonstrated to indicate the efficacy of the treatment. This study investigated photobleaching during light irradiation. Methods A validated non-invasive fluorescence imaging system was utilised to monitor changes in PpIX fluorescence during light irradiation. Fifty patients were recruited to this study, with patients monitored before, during (forty patients at the half way stage and ten at regular intervals in the initial phase of treatment) and after light irradiation. Results Phased PpIX photobleaching was observed during light irradiation with a significantly greater change ( P < 0.001) in PpIX photobleaching during the first half of light treatment. Within the ten patients monitored periodically the phased photobleaching observed fitted a double exponential decay curve ( r2 = 0.99, P < 0.005) suggesting a rapid initial phase of reaction when the light treatment was commenced. Conclusions Photobleaching was observed to be maximal in the initial phases of treatment, however photobleaching of PpIX continued until the completion of light treatment indicating that current clinical protocols for MAL-PDT do not over-treat the lesion with light.