In vivo light dosimetry for motexafin lutetium‐mediated PDT of recurrent breast cancer

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Abstract
Background and Objectives To measure the fluence at tissue surface for patients in our Phase II clinical trial of motexafin lutetium (MLu)‐mediated chest wall photodynamic therapy for recurrent breast carcinoma and to compare it to the calculated irradiance. Study Design/Materials and Methods The spatial and time dependence of light fluence (rate) was monitored in vivo on the chest wall surface using isotropic detectors in five patients. Patients were given MLu either 4 mg/kg with light at 18 hours or 5 mg/kg with light at 24 hours using an irradiance of 150 J/cm2 at 730 nm, with an incident fluence rate of 75 mW/cm2. The ratio of fluence rate to the incident fluence rate was determined at the center of the treatment field. This ratio was used to estimate the effective attenuation coefficient, μeff. Results The mean and standard deviation of the ratio for all patients was 1.6 ± 0.2. The corresponding range of μeff was between 0.87 and 2.1 cm−1, assuming reduced scattering coefficient, μ′s = 4 cm−1. Conclusions A conversion factor was determined to convert the irradiance to fluence rate on the tissue surface. However, the fluence (or the ratio) on patient surface varied by 70% due to the heterogeneity of optical properties. This supports the use of real‐time in vivo dosimetry during photodynamic therapy. Lasers Surg. Med. 31:305–312, 2002.