Backscatter factors for diagnostic radiology (1-4 mm Al HVL).

Backscatter factors (BSF) in the diagnostic radiology quality range (1-4 mm Al) have been determined by ionisation chamber and TLD techniques. Ionisation chamber measurements are subject to systematic errors due to displacement of the scattering medium, although high precision allows the demonstration of the kVp dependence of BSF for a given first HVL. TLD techniques lead to a reduction of these systematic errors although the read-out procedures lead to lower precision than ionisation chamber measurements. Comparison of the TLD-based measurements with the data of Br. J. Radiol. Supplement 11 indicates good agreement (less than 2%) for HVLS greater than 2 mm Al and field sizes greater than 10 cm x 10 cm. Comparison with the work of other authors not covered by Supplement 11 indicates, in general, good agreement only where kVp-filter combinations are similar. The importance is stressed of taking into account the kVp-filter combination when defining the quality of an X-ray beam.