Three-dimensional radiation dosimetry with optical projection tomography

Here we present initial results on the study of the dosimetric properties of a normoxic N-Vinylpyrrolidone based polymer gel dosimeter using a newly developed optical projection tomography (OPT) system. The system employs a sensitive CCD camera, a rotation stage allowing full 360 deg rotation and a wide field homogeneous light source which transilluminates the gel sample. This setup is capable of producing high resolution images of the light attenuation map inside the sample's volume in three dimensions (3D). The experimental procedure involves the capturing of two-dimensional projection images of the polymer sample in rotation steps of 1 deg. Data analysis is performed by back projecting the photons using an inverse Radon transform resulting in the reconstruction of 3D images of the attenuation coefficient. The resulting 3D attenuation map of the irradiated volume can be directly correlated to the radiation dose imparted. The OPT system may operate in 'dry' conditions without the use of any refractive index matching fluids. The sensitivity and dynamic range offered by the methodology covers the range of radiotherapy doses in modern clinical practice.