Cherenkov light emission from tissue undergoing radiation therapy is a complex function of the dose deposition and is reduced by the optical attenuation of the tissue. A diffusion theory based integral of the remitted light is presented, using the assumption that only Cherenkov photons from the first 8 mm of tissue are able to appreciably escape from the surface. This depth restriction falls within the linear build-up region for both electron and photon beams used in radiotherapy. The resulting expression for Cherenkov light fluence formulated here indicates that the outgoing intensity is dependent upon the quasi-linear dose build up gradient (k2) in the first 8 mm of tissue, is inversely proportional to the optical absorption (μa), and is relatively independent of the scattering coefficient (μs/ ). Numerical evaluation suggests that the diffuse component of Cherenkov light emission dominates over any unscattered photons, suggesting that the radiation build-up factor dominates what is imaged off the surface. This observation could allow for linear corrections to Cherenkov images with knowledge of tissue optical properties and for better interpretation of the origin of Cherenkov from tissue.