The title of the PhD Dissertation is: Dosimetry and Real-Time Monitoring of Phototherapy Procedures
Committee:
Anna Yaroslavsky, Ph.D., Professor, Director - Advanced Biophotonics Laboratory, Department of Physics & Applied Physics, University of Massachusetts Lowell
Erno Sajo, Ph.D., Professor, Director – Medical Physics, Department of Physics & Applied Physics, University of Massachusetts Lowell
Cecil Joseph, Ph.D., Assistant Teaching Professor, Department of Physics & Applied Physics, University of Massachusetts Lowell
Title: Dosimetry and Real-Time Monitoring of Phototherapy Procedures
Abstract:
This collection of works presents a universal treatment protocol for oral mucositis using extraoral photobiomodulation therapy (PBMT). The dissertation also investigates the use of reflectance for real-time optical temperature measurements. Without a dosimetric plan, phototherapy can either under-treat (fail to provide the efficacious dose) or over-treat (excessive heating of surrounding tissue). It is important, then, to establish a protocol prior to its performance in the clinic, and to monitor progress during the procedure. The first published work in this collection validates the Monte Carlo method used to develop an extraoral PBMT treatment protocol. Four subjects were recruited for this study. Magnetic Resonance Imaging (MRI) scans were acquired of each subject’s cheek. Tissues found were identified, and their thicknesses measured. This anatomical information was used to construct a model for the Monte Carlo simulations. In vivo transmittance measurements were performed through each subject’s cheek for comparison. Simulation results were found to differ by at most 12% to the measured transmittance. This quantifies the accuracy of this Monte Carlo method, validating its use to prepare a universal treatment for extraoral PBMT. The second publication proposes a universal treatment protocol for oral mucositis using extraoral PBMT. The Monte Carlo method from the first publication was used to determine the distribution of 850 nm light through four possible treatment sites. Anatomical data from archival MRI and optical properties from the literature were used as a model. Results indicate that the total tissue thickness had the greatest effect on fluence rates at the oral mucosa. Fluence rates varied due to large anatomical differences between patients. The universal protocol was established using median treatment times. It was found that an efficacious dose between 1 J/cm2 and 6 J/cm2 can be delivered within 15 minutes for all four sites. The third and last publication presents a method for measuring tissue temperature in real time from reflectance spectra. Reflectance spectra of ex vivo skin samples were acquired. Samples were illuminated in a 4 mm diameter spot size using a halogen lamp. Remitted light was collected by a fiber optic, which was positioned at angles 10°, 20°, and 30° relative to the sample’s normal. Collected light in the 900-1650 nm range was analyzed using a grating spectrometer. Measurements were made as samples were heated to and maintained at temperatures between 20 °C and 60 °C. Reflectance minima corresponding to water absorption peaks experienced blue shifts as sample temperatures increased. These blue shifts were greatest for the absorption peak near 1450 nm. Differences found between fiber optic angles were not statistically significant. However, greater mean shifts were found using smaller fiber optic angles. The first two papers develop and determine the accuracy of a universal treatment protocol for extraoral PBMT using Monte Carlo simulations. The last paper gives a potential method for measuring tissue temperature in real time using reflectance measurements. Together, this collection of works provides methods to help ensure a proper dose is provided both before and during phototherapy procedures.