Rustgi S N, Rodgers J E
Department of Radiation Medicine, Georgetown University Hospital, Washington, D.C. 20007.
Med Phys. 1987 Sep-Oct;14(5):884-8. doi: 10.1118/1.596018.
The magnitude of the bremsstrahlung component in the 6-18 MeV electron beams from a Varian Clinac 18 accelerator was measured directly using a 0.16 T magnetic field to deflect the electron beams. The central axis depth ionization curves were measured at 130- and 197-cm source-surface distances in a Therados RFA-3 water phantom with and without the magnet being placed between the 4 X 4 cm2 electron cone and the water phantom. Results obtained clearly demonstrate that the bremsstrahlung component is primarily (greater than 90%) generated in the electron scattering-foil/collimation system and not in the water phantom. The x-ray central axis depth ionization curves exhibit buildup and attenuation regions characteristic of megavoltage x-ray beams. Ionization profiles of the x-ray component, measured in a plane perpendicular to the central axis, were also examined. Analysis of bremsstrahlung production as a function of photon collimation jaw opening shows a strong dependence, especially for the smaller openings.
