Doppler optical coherence tomography onitors microvascular changes during photodynamic herapy in a Dunning prostate model under arying treatment conditions eau

ictor X. D. Yang ntario Cancer Institute niversity of Toronto epartment of Medical Biophysics oronto, Ontario M5G 2M9 anada and yerson University epartment of Physics oronto, Ontario M5B 2K3 anada and unnybrook Health Science Center maging Research oronto, Ontario M4N 3M5 Abstract. We measure the tumor vascular response to varying irradiance rates during photodynamic therapy PDT in a Dunning rat prostate model with interstitial Doppler optical coherence tomography IS-DOCT . Rats are given a photosensitizer drug, Photofrin, and the tumors are exposed to light 635 nm with irradiance rates ranging from 8 to 133 mW/cm2 for 25 min, corresponding to total irradiance of 12 to 200 J /cm2 measured at surface . The vascular index computed from IS-DOCT results shows the irradiance rate and total irradiance dependent microvascular shutdown in the tumor tissue during PDT. While faster rates of vascular shutdown were associated with increasing PDT irradiance rate and total irradiance, a threshold effect was observed as irradiance rates above 66 mW/cm2 surface , where no further increase in vascular shutdown rate was detected. The maximum post-treatment vascular shutdown 81% without immediate microcirculatory recovery was reached with the PDT condition of 33 mW/cm2 and 50 J /cm2. Control groups without Photofrin show no significant microvascular changes. Microvascular shutdown occurs at different rates and shows correlation with PDT total irradiance and irradiance rates. These dependencies may play an important role in PDT treatment planning, feedback control for treatment optimization, and post-treatment assessment. © 2007 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2744068