Figure 3.
A, Gantry star shot image when the X-ray tube is rotated from the vertical to the horizontal position using 1-mm collimator. B, Image illustrates the 0.5-mm-diameter X-ray beam alignment with respect to the robot rotation axis. The beam intersects within ±0.20 mm at isocenter. C, Image shows microbeam square grid pattern from 0.5-mm-diameter collimator at isocenter (100 kV, 6 mA with 1 minute exposure) measured using Gafchromic film placed at 1 cm below isocenter. For 10 × 10 mm2 spatially fractionated radiation therapy (GRID), the rows are separated by 1 mm. The surface plot of relative optical density distribution of corresponding grid patterns is also shown.