Diagram of the gated MV CBCT system. The radiation beam of the LINAC is stopped when either the “Synchronization circuit” or the “Gating computer” asserts the beam hold-off line.
Axial slices of the MV CBCT scans of the contrast detail phantom for (a) nongated data acquisition, , (b) continuous rotation-gated acquisition, gaps, respiratory cycle and duty cycle 33%, , and (c) gated rotation-continuous acquisition, same respiratory cycle and duty factor, . Numbers in (a) are the electron densities of the inserts, relative to background (solid water).
Contrast-to-noise ratios (CNRs) of the inserts of the contrast detail phantom in Fig. 2 for the nongated acquisition, continuous rotation-gated acquisition, and gated rotation-continuous acquisition schemes.
Axial sections from the MV CBCT scans of the thoracic phantom. (a) Nongated data acquisition. (b) Continuous rotation-gated acquisition, gaps. (c) Gated rotation-continuous acquisition. Total beam-on time is approximately for all scans. The objects indicated by arrows are used to simulate the tumors although the difference or 10% contrast between these objects and the surrounding lung is much smaller than the difference for actual lung tumors.
Coronal sections from the MV CBCT scans of the thoracic phan tom. (a) Nongated data acquisition. (b) Continuous rotation-gated acquisition, gaps. (c) Gated rotation-continuous acquisition. Total beam-on time is approximately for all scans. The arrows indicate tumor-like objects, as explained in Fig. 4.
Axial sections of a lung cancer patient. (a) Simulation CT scan. (b) MV CBCT continuous rotation-gated acquisition. (c) MV CBCT gated rotation-continuous acquisition. Total beam-on time is approximately for b and c. The arrow points to the target on the simulation CT scan and the MV CBCT scan. (d) The gated lateral port film of the same patient, where the target is difficult to identify.
Reconstructed coronal sections of a lung cancer patient using nongated (a) diagnostic CT and (b) MV CBCT. Significant motion artifacts are present in both scans. (c) A gated scan of another lung cancer patient using MV CBCT. Motion artifacts are reduced and the diaphragm is clearly identified.
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