This work aims at characterizing how light propagates through bone in order to efficiently guide treatment of
osteosarcoma with photodynamic therapy (PDT). Optical properties of various bone tissues need to be characterized in
order to have a working model of light propagation in bone. Bone tissues of particular interest include cortical bone, red
and yellow marrow, cancellous bone, and bone cancers themselves. With adequate knowledge of optical properties of
osseous tissues, light dosimetry can determine how best to deliver adequate light to achieve phototoxic effects within
bone. An optical fiber source-collector pair is used for diffuse reflectance spectroscopic measurements in order to
determine the scattering and absorption properties of bone tissues. Native absorbers of interest at visible and near-IR
wavelengths include water and oxygenated and deoxygenated hemoglobin. A cylindrically symmetric Monte Carlo
model is then used, incorporating these results, in order to predict and guide the delivery of light within bone in order to
achieve the desired phototoxic effect in PDT.
Sarcoids are a locally invasive cutaneous fibroblastic neoplasia and are the most common skin tumor of equids. Myriad treatments are described in the literature including surgery, topical blistering agents, cryosurgery, immunotherapy, and intralesional chemotherapy. Recurrence or progression of the disease after treatment is common. Two years ago the authors began clinical trials investigating the feasibility of photodynamic therapy for the treatment of sarcoid tumors. The tumor or surgical margins were treated using topical or intra-lesional delta-aminolevulinic acid (ALA) as a photosensitizing agent. The ALA was left in situ for a period of time allowing buildup of protoporphyrin IX (the photosensitizer) prior to irradiation with a 635-nm diode laser. We have initial results in 10 patients with 18 lesions and have seen decrease in tumor size or complete remission in 13 of 18 lesions. Recurrence or progression has been noted in 7 lesions. Results of these trials and follow-up information on clinical patients will be presented for review.