Beam and tissue factors affecting Cherenkov image intensity for quantitative entrance and exit dosimetry on human tissue.

Abstract

This study's goal was to determine how Cherenkov radiation emission observed in radiotherapy is affected by predictable factors expected in patient imaging. Factors such as tissue optical properties, radiation beam properties, thickness of tissues, entrance/exit geometry, curved surface effects, curvature and imaging angles were investigated through Monte Carlo simulations. The largest physical cause of variation of the correlation ratio between of Cherenkov emission and dose was the entrance/exit geometry (˜50%). The largest human tissue effect was from different optical properties (˜45%). Beyond these, clinical beam energy varies the correlation ratio significantly (˜20% for X-ray beams), followed by curved surfaces (˜15% for X-ray beams and ˜8% for electron beams), and finally, the effect of field size (˜5% for X-ray beams). Other investigated factors which caused variations less than 5% were tissue thicknesses and source to surface distance. The effect of non-Lambertian emission was negligible for imaging angles smaller than 60 degrees. The spectrum of Cherenkov emission tends to blue-shift along the curved surface. A simple normalization approach based on the reflectance image was experimentally validated by imaging a range of tissue phantoms, as a first order correction for different tissue optical properties.