Measurement of backscatter factors for low energy radiotherapy (0.1-2.0 mm Al HVL) using thermoluminescence dosimetry.

Significant discrepancies of up to 10% exist between backscatter factors (BSF) recommended in a recent IAEA dosimetry Code of Practice (1987) compared with those published in Br. J. Radiol. Supplement 17 (1983), for the x-ray quality range 0.1-2.0 mm Al HVL. In an attempt to resolve this discrepancy, BSFs have been measured using thermoluminescence dosimetry (TLD) with small lithium borate chips, in order to minimise displacement effects associated with the use of larger volume ionisation chambers. Although subject to uncertainties inherent in the TLD calibration and readout process, the results indicate that the BJR (1983) data overestimate BSFs in this quality range. Broad agreement with the IAEA data is indicated, for the limited number of x-ray qualities and field sizes used.