Light dosimetry in vivo

Area of Science:

• Biomedical Optics
• Photodynamic Therapy Dosimetry
• Tissue Optics

Background:

• In vivo light dosimetry is crucial for applications like photodynamic therapy (PDT).
• Accurate light distribution measurements in tissues depend on understanding optical properties and light transport models.
• Previous studies have focused on defining key optical quantities and measurement techniques.

Purpose of the Study:

• To define essential quantities for in vivo light dosimetry, including radiance and fluence rate.
• To review methods for estimating light distribution in tissues, from model calculations to direct measurements.
• To investigate the importance of detailed scattering function knowledge for accurate surface fluence rate calculations.

Main Methods:

• Discussion of tissue optical properties (absorption, scattering) and their measurement.
• Review of light transport models: diffusion theory, P3-approximation, and Monte Carlo simulations.
• Description of fiber-optic probe construction, calibration, and use for in vivo fluence rate measurements.

Main Results:

• Accurate calculation of fluence rate near the tissue surface requires detailed scattering function knowledge, particularly for forward scattering tissues.
• Deeper within the tissue, the product of scattering coefficient and (1-g) is sufficient for calculations.
• Minimally invasive absolute fluence rate measurements achieve 10-20% accuracy.
• In situ measurements are vital due to inter-patient and intra-patient variability in tissue optical properties and treatment-induced changes.

Conclusions:

• Precise in vivo light dosimetry, especially for PDT, necessitates accurate knowledge of tissue optical properties and in situ measurements.
• While fluence rate measurements are improving, photosensitizer dosimetry remains a developing area in PDT.
• Understanding light scattering is critical for accurate dosimetry, particularly at the tissue surface.