Room: Davidson Ballroom B
Purpose: To develop and validate a mathematical deconvolution formulation to solve for dose deposition in a superficial region and Cerenkov photon emission from a phantom material under external beam irradiation.
Methods: An integral equation was derived to represent a Cerenkov photon image acquired by a camera for an incident high-energy photon beam using convolution kernels. Subsequently, we obtained an equation relating the planar dose at a depth to a Cerenkov photon image using the well-known relationship between the incident beam fluence and the dose distribution in a medium. These equations contained two convolution kernels called the Cerenkov scatter function (CSF) and the Dose scatter function (DSF). The DSF is well characterized in literature, however the CSF is novel and pertains only to Cerenkov light transport. Solutions for the CSF and DSF were generated using GAMOS, a Geant4-based Monte Carlo software. The theoretical formulation was experimentally evaluated by using an optical phantom irradiated with high energy photon beams. The solution for planar dose delivered to the phantom was obtained from Cerenkov photon images taken during irradiation using an iterative deconvolution method with the CSF and DSF.
Results: The intensity of the deconvolved Cerenkov photon images showed linear dependence on the dose rate and the photon beam energy. The relative intensity showed a field size dependence similar to the beam output factor. Deconvolved Cerenkov images showed improvement in dose profiles compared with the raw image data. In particular, deconvolution significantly improved the agreement in the high dose gradient region, such as in the penumbra. Two-dimensional dose distributions of the deconvolved Cerenkov images agreed well with the reference distributions.
Conclusion: The deconvolution method improved the overall accuracy of using Cerenkov photon images taken during external beam radiation to solve for superficial dose deposition.