Phantom geometry, coordinate system, and beam directions.
Schematic of nozzle geometry.
Fluoroscopic images of gold markers in pelvic phantom (100 kV, 80 mAs, 4 ms (AP), 120 kV, 80 mAs, 4 ms (LR)). The arrows show 1.5-mm markers; other dots are 2-mm markers. Two coiled markers with a diameter of 1.5 mm are also shown for comparison.
The marker positions investigated. Rectangles show PTV region and its side length is L = 3.6–4.8 cm. ξ = 1.5 cm, η = 1.0 cm.
TCP curve for α/β values of 1.5, 3, and 10 Gy (RBE) for homogeneous dose distribution.
Depth dose distribution along the central beam axis for gold markers with a diameter of 2 mm (left) and 1.5 mm (right). Three plots for one lateral field with marker positions (A), (C), and (E) in Fig. 4(a) are shown with the reference (without marker). The dose values at the marker positions (arrows) have no effect on TCP evaluation. In the plots, these values are removed and the endpoints are linearly interpolated. Note that the peak-to-plateau ratio is rather high because the profile is taken along the central axis of the pencil beam as well as the source to axis distance is rather small in our nozzle.
Plane dose distribution for one (a), two opposite (b), and three fields (c) along the central beam axis for gold markers with a diameter of 2 mm placed at the IC. Rectangular regions and black dots show the PTV and gold marker, respectively.
Simulation setup for beam widths verifications in a phantom composed of water and gold plate. (a) 180 MeV and (b) 132 MeV beam enters the water phantom, passes through the gold plate of 2 mm thickness, and stops at 20 and 11 cm depth, respectively.
Radiobiological parameters used in this study.
Summary of minimum dose in CTVave (D min) and the minimum value of R TCP among CTVmin, CTVave, and CTVmax (R V TCP) for each α/β value and for each marker size, position, and number of fields.
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