MEASURED SCATTERED X-RAY-ENERGY SPECTRA FOR SIMULATED IRRADIATION GEOMETRIES IN DIAGNOSTIC-RADIOLOGY

In this study, scattered x-ray distributions were produced by irradiat ing an anthropomorphic pelvis phantom under fluoroscopic conditions us ing incident beams generated at tube potentials between 61 kV(p) and 1 12 kV(p). Both overcouch and undercouch x-ray tube orientations were u sed when irradiating the phantom. The energy spectrum of the scattered x rays was measured with a germanium x-ray detector. Two measurement geometries were employed: (i) the detector placed at 90 degrees to the incident x-ray beam to determine the energy spectra incident on the t runk region of staff and (ii) the detector placed at 45 degrees to the x-ray beam, measuring spectra incident on the head and neck region. T he effect of irradiation area on the scattered spectra was also invest igated. Spectral distributions, along with mean energy and half-value layer (HVL) in mm Al, are presented for each spectrum. Energy spectra measured at 90 degrees to the incident x-ray beam were found to have H VLs approximately 10%-15% greater than the corresponding primary incid ent spectrum, for both overcouch and undercouch irradiations. The magn itude of the irradiation area had negligible effect on the mean energy and HVL of the spectra. (C) 1996 American Association of Physicists i n Medicine.