http://repub.eur.nl/res/aut/12274/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/10483/ 2006-06-27T00:00:00Z The interaction of light with tissue and its use for medical purposes has been under investigation for centuries. Since the early nineteen sixties, the development of novel optical technology and advances in laser design/technology allowed a wide range of innovative applications in many fields of medicine. For the majority of light applications in medicine the distribution of light within tissue is of fundamental importance. The light distribution is determined by the optical properties of the tissue; scattering and absorption. This thesis focuses on two applications of light in medicine, photodynamic therapy (PDT) and optical diagnostics. For each application the effect of differences in and changes of tissue optical properties are investigated. The distribution of light within tissue is of vital importance in PDT and is strongly dependent on the in vivo optical properties. In vivo differences and variations in optical properties are also critically important for optical diagnostics. The hypothesis presented is that the underlying cause of the current limitations in clinical PDT and low sensitivity in optical diagnosis are due to the heterogeneous and dynamic nature of tissue optical properties. This thesis tests this hypothesis by investigating the spatial distribution, inter patient differences, and temporal behaviour of in vivo optical properties by means of in vivo light measurement. http://repub.eur.nl/res/pub/8296/ 2004-01-01T00:00:00Z BACKGROUND: Photochemical and thermal methods are used for ablating Barrett's oesophagus (BO). The aim of this study was to compare 5-aminolevulinic acid induced photodynamic therapy (ALA-PDT) with argon plasma coagulation (APC) with respect to complete reversal of BO. METHODS: Patients with BO (32 no dysplasia and eight low grade dysplasia) were randomised to one of three treatments: (a) ALA-PDT as a single dose of 100 J/cm(2) at four hours (PDT100; n = 13); (b) ALA-PDT as a fractionated dose of 20 and 100 J/cm(2) at one and four hours, respectively (PDT20+100; n = 13); or (c) APC at a power setting of 65 W in two sessions (APC; n = 14). If complete elimination of BO was not achieved by the designated treatment, the remaining BO was treated by a maximum of two sessions of APC. RESULTS: Mean endoscopic reduction of BO at six weeks was 51% (range 20-100%) in the PDT100 group, 86% (range 0-100%) in the PDT20+100 group, and 93% (range 40-100%) in the APC group (PDT100 v PDT20+100, p<0.005; PDT100 v APC, p<0.005; and PDT20+100 v APC, NS) with histologically complete ablation in 1/13 (8%) patients in the PDT100 group, 4/12 (33%) in the PDT20+100 group, and 5/14 (36%) in the APC group (NS). Remaining BO was additionally treated with APC in 23/40 (58%) patients. Histological examination at 12 months revealed complete ablation in 9/11 (82%) patients in the PDT100 group, in 9/10 (90%) patients in the PDT20+100 group, and in 8/12 (67%) patients in the APC group (NS). At 12 months, no dysplasia was detected. Side effects (that is, pain (p<0.01), and nausea and vomiting (p<0.05)) and elevated liver transaminases (p<0.01) were more common after PDT than APC therapy. One patient died three days after treatment with PDT, presumably from cardiac arrhythmia. CONCLUSION: APC alone or ALA-PDT in combination with APC can lead to complete reversal of Barrett's epithelium in at least two thirds of patients when administered in multiple treatment sessions. As the goal of treatment should be complete reversal of Barrett's epithelium, we do not recommend these techniques for the prophylactic ablation of BO.