Protoporphyrin IX fluorescence photobleaching increases with the use of fractionated irradiation in the esophagus.
Fluorescence measurements have been used to track the dosimetry of photodynamic therapy (PDT) for many years, and this approach can be especially important for treatments with aminolevulinic-acid-induced protoporphyrin IX (ALA-PpIX). PpIX photobleaches rapidly, and the bleaching is known to be oxygen dependent, and at the same time, fractionation or reduced irradiance treatments have been shown to significantly increase efficacy. Thus, in vivo measurement of either the bleaching rate and/or the total bleaching yield could be used to track the deposited dose in tissue and determine the optimal treatment plans. Fluorescence in rat esophagus and human Barrett's esophagus are measured during PDT in both continuous and fractionated light delivery treatment, and the bleaching is quantified. Reducing the optical irradiance from 50 to 25 mWcm did not significantly alter photobleaching in rat esophagus, but fractionation of the light at 1-min on and off intervals did increase photobleaching up to 10% more (p value=0.02) and up to 25% more in the human Barrett's tissue (p value<0.001). While two different tissues and two different dosimetry systems are used, the data support the overall hypothesis that light fractionation in ALA-PpIX PDT esophageal treatments should have a beneficial effect on the total treatment effect.
Pogue
Brian W
BW
Dartmouth College, Thayer School of Engineering, Hanover, New Hampshire 03755, USA. pogue@dartmouth.edu
Sheng
Chao
C
Benevides
Juan
J
Forcione
David
D
Puricelli
Bill
B
Nishioka
Norm
N
Hasan
Tayyaba
T
D000818:Animals; D001528:Behcet Syndrome / Q000188:drug therapy* / Q000378:metabolism*; D019583:Dose Fractionation, Radiation; D004305:Dose-Response Relationship, Drug; D004947:Esophagus / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D008657:Metabolic Clearance Rate / Q000187:drug effects; D038761:Photobleaching / Q000528:radiation effects; D011379:Prognosis; D011524:Protoporphyrins / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D011879:Radiotherapy Dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D013050:Spectrometry, Fluorescence / Q000379:methods*; D016896:Treatment Outcome
D011524:Protoporphyrins; C028025:protoporphyrin IX