Figure 6.

Doses (CTDI_∞) in infinitely long cylindrical phantoms for PMMA and with the body bow tie filter are shown for different monoenergetic x-ray beams. The ability of the lower energy photons to penetrate to the center to contribute to dose decreases with diameter, as expected, however even the 30 keV beam is capable of delivering reasonable radiation dose levels to the edge location on the phantom. The higher energy x-ray beams produce more scattered radiation, and hence a “bump” in the dose coefficient is seen for diameters from 10 to 70 mm.