The OCTOPUS-ONE
TM
research laser CT scanner developed and manufactured by MGS Research, Inc. (Madison, CT) has been evaluated.
The scanner is designed for imaging BANG

polymer gels for the measurement of 3D-dose distributions. The scanner operates in a translaterotate configuration with a single scanning laser beam. Filtered backprojection is used to reconstruct projection data in each plane. The OD reconstruction algorithms were tested using mathematically defined OD distributions and found to be correctly reconstructed within 0.5%.
The mechanical and optical setup, projection centering on the axis of rotation, linearity, spatial resolution, and the reconstruction algorithm were tested. The scanner light detector response was linear with respect to light intensity. The laser’s horizontal and vertical full width at half maximums were 0.6 and 0.8 mm, respectively. Dose calibration tests of the gel were performed using a 9-field (2 x 2 cm
2
each) dose pattern irradiated with dose levels from 0 to 186 cGy, calibrated using radiochromic film, and the calibration curve was applied to a gel irradiated with a 5 x 5 cm
2
6 MV field. The gel-derived dose distribution agreed well with the radiochromic film measurement to within a normalization of
1.15. After renormalization, the multidimensional dose comparison tool
γ
was
γ
< 1.3 using 5% and 1.5 mm criteria. The optical CT scanner shows potential to provide accurate 3D dosimetry, but more validation is required to determine the cause of existing discrepancies. This work was supported in part by NIH R01 CA84409 and by MGS Inc.