Backscatter factor measurements for kilovoltage X-ray beams using thermoluminescent dosimeters (TLDs)

Backscatter factors (BSF) are used for calculation of absorbed dose in water from kilovoltage x-ray beams through the measurements using air-kerma based dosimetry protocols. The determination of backscatter factors has usually been performed using Monte Carlo calculations. The experimental measurement of BSFs requires that a dosimeter causes minimal perturbation to the x-ray fluence. In this work, we present the results of measuring BSFs using two different thermoluminescent dosimeters (TLDs). These were LiF:Mg,Ti (TLD100) and LiF:Mg,Cu,P (TLD100H) for x-ray beams with energies ranging from 75 to 300 kVp. We also calculated the BSFs for these x-ray beams using the EGSnrc Monte Carlo code and compared our results with published BSFs. With the exception of the 180 kVp x-ray beam (HVL 0.85 mm Cu), the BSFs measured with both materials agree to within 5% of the BSFs published in IPEMB and AAPM protocols and calculated by Monte Carlo simulations. From these results, we propose that BSFs can be readily determined using measurements with TLD100 and TLD100H chips for comparison with published BSFs. (C) 2011 Published by Elsevier Ltd.