RESUMO
Successful outcome of Photodynamic therapy (PDT) depends on accurate delivery of prescribed light dose. A quality assurance program is necessary to ensure that light dosimetry is correctly measured. We have instituted a QA program that include examination of long term calibration uncertainty of isotropic detectors for light fluence rate, power meter head intercomparison for laser power, stability of the light-emitting diode (LED) light source integrating sphere as a light fluence standard, laser output and calibration of in-vivo reflective fluorescence and absorption spectrometers. We examined the long term calibration uncertainty of isotropic detector sensitivity, defined as fluence rate per voltage. We calibrate the detector using the known calibrated light fluence rate of the LED light source built into an internally baffled 4â³ integrating sphere. LED light sources were examined using a 1mm diameter isotropic detector calibrated in a collimated beam. Wavelengths varying from 632nm to 690nm were used. The internal LED method gives an overall calibration accuracy of ±4%. Intercomparison among power meters was performed to determine the consistency of laser power and light fluence rate measured among different power meters. Power and fluence readings were measured and compared among detectors. A comparison of power and fluence reading among several power heads shows long term consistency for power and light fluence rate calibration to within 3% regardless of wavelength. The standard LED light source is used to calibrate the transmission difference between different channels for the diffuse reflective absorption and fluorescence contact probe as well as isotropic detectors used in PDT dose dosimeter.
RESUMO
BACKGROUND: Sunlight can activate photodynamic therapy (PDT), and this is a proven strategy to reduce pain caused byconventional PDT treatment, but assessment of this and other alternative low dose rate light sources, and their efficacy, has not been studied in an objective, controlled pre-clinical setting. This study used three objective assays to assess the efficacy of different PDT treatment regimens, using PpIX fluorescence as a photophysical measure, STAT3 cross-linking as a photochemical measure, and keratinocyte damage as a photobiological measure. METHODS: Nude mouse skin was used along with in vivo measures of photosensitizer fluorescence, keratinocyte nucleus damage from pathology, and STAT3 cross-linking from Western blot analysis. Light sources compared included a low fluence rate red LED panel, compact fluorescent bulbs, halogen bulbs and direct sunlight, as compared to traditional PDT delivery with conventional and fractionated high fluence rate red LED light delivery. RESULTS: Of the three biomarkers, two had strong correlation to the PpIX-weighted light dose, which is calculated as the product of the treatment light dose (J/cm2) and the normalized PpIX absorption spectra. Comparison of STAT3 cross-linking to PpIX-weighted light dose had an R=0.74, and comparison of keratinocyte nuclear damage R=0.70. There was little correlation to PpIX fluorescence. These assays indicate most of the low fluence rate treatment modalities were as effective as conventional PDT, while fractionated PDT showed the most damage. CONCLUSIONS: Daylight or artificial light PDT provides an alternative schedule for delivery of drug-light treatment, and this pre-clinical assay demonstrated that in vivo assays of damage could be used to objectively predict a clinical outcome in this altered delivery process.