Technical Note: A fast laser‐based optical‐CT scanner for three‐dimensional radiation dosimetry

Abstract

To introduce a novel laser-based optical-CT scanner for the readout of three-dimensional (3D) radiation dosimeters. The scanner employs a diode laser, a cylindrical lens, a motorized linear rail, a rotation stage, and a charge-coupled device camera. The scanner operates in a translate-rotate fashion and may be set up in two configurations depending on the orientation of the cylindrical lens. The attenuation coefficient versus dose response was determined for a normoxic N-vinylpyrrolidone based polymer gel dosimeter. Cylindrical dosimeters, 2 cm diameter, were homogenously irradiated to known doses up to 60 Gy using a 6 MV linear accelerator. For a test irradiation, a 5 cm diameter dosimeter was irradiated along its cylindrical axis using a rectangular 1 cm x 1 cm irradiation beam. The dose readout of this scanner was compared to the corresponding readout of a common wide illumination and area detector optical-CT scanner. The attenuation coefficient versus dose response of the laser-based system was found to be linear up to 60 Gy (r2 = 0.997) compared to the wide field illumination based optical-CT scanner, which exhibits linearity up to 32 Gy (r2 = 0.996). The noise in the reconstructed attenuation coefficient maps was +/- 7.2 x 10(-2) mm(-1) versus +/- 9.5 x 10(-3) mm(-1) for the laser-based system and the wide field illumination system, respectively. We have developed a novel laser-based optical-CT scanner, which is capable of generating fast 3D dosimetric data using a scattering polymer gel dosimeter. Our data demonstrate that the dose readout of this scanner preserves the advantage of existing laser-based optical-CT scanners in providing measurements, which are minimally affected by scattered light. For accurate reconstruction of the attenuation coefficients, noise reduction techniques need to be applied.