On-line dosimetry for photodynamic therapy: part I--incident irradiance versus space irradiance for human skin

One of the key components of photodynamic therapy dosimetry studies is the actual light dose delivered to the tissue at a targeted, therapeutic depth. The light dose delivered to the tissue is dependent upon the incident irradiance at the initial point of light application as well as the tissue optical properties. Since the parameters defining the light and therapeutic dose may vary between subjects and treatment sites as well as during treatment, it is advantageous to monitor the dosimetry during photodynamic therapy. The objective of this work is to develop methodologies and systems to enable on-line dosimetry. This initial study examines the relationship between incident irradiance and space irradiance for cutaneous areas in various humans. Space irradiance levels (mW/cm2) were measured on the skin surface of 30 subjects using isotropic fiber optic probes (0.8 mm) and were compared to incident irradiance levels. Space irradiance values were obtained from various anatomical locations on each subject during surface illumination (664 plus or minus 7 nm) using an incident irradiance of 100 mW/cm2. The results demonstrate ratios of space irradiance: incident irradiance from 1.49 to 2.35 for all cutaneous areas. Abnormal skin features, such as scars, birthmarks, moles, freckles, etc., on the arm demonstrated ratios ranging from 1.58 to 1.84. Variances observed within and between subjects demonstrate the need for accurate dosimetry monitoring during therapy. A larger study is planned to fully characterize space irradiance variations in normal skin as well as cutaneous lesions in additional subjects.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.