Calculation of the backscatter factors for spectral beams in diagnostic radiology

Backscatter factors (BSFs) have been calculated for homogeneous slab phantoms of water, and the materials ICRU and PMMA. The BSFs have been calculated for X-ray spectral beams for Diagnostic Radiology, with focus to phantom distances of 50, 100, 150 cm, field sizes of 10 x 10, 20 x 20, 25 x 25 cm2. BSFs monoenergetic beams under mentioned conditions were computed through the Monte Carlo method using the ITS 3.0 program. BSFs for spectral beams were theoretically derived from those for monoenergetic radiation and the spectra data. The spectral distribution as a function of energy was calculated with the Birch and Marshall method. BSFs were obtained with statistical uncertainties of 1% and are in good agreement with results published by other authors (deviations less than 2%). These results complement the existing data for Diagnostic Radiology and are essential for calibration of dosimeters making measures of the entrance surface dose to patients, as required in recent international recommendations. (author)