The energy correction factor of LiF thermoluminescent dosemeters in megavoltage electron beams: Monte Carlo simulations and experiments.

The energy correction factor of LiF thermoluminescent dosemeters (TLDs) calibrated in Co-60 gamma-rays and used for measurements in megavoltage electron beams has been determined experimentally and theoretically using Monte Carlo simulations. The experiments show that the energy correction factor of 1 mm thick TLD-100 has an average for both rods and chips which varies from 1.036 +/- 1.3% (1 SD) for 4 MeV electron beams to 1.021 +/- 1.3% (1 SD) for 20 MeV electron beams for measurement performed at dmax in PMMA (Perspex). The results of the Monte Carlo simulations were within 0.6% of the experimental results and ranged from 1.041 +/- 0.9% (1 SD) for 2 MeV electrons to 1.028 +/- 0.8% (1 SD) for 20 MeV electron beams. There was no significant difference in the energy correction factors of LiF TLDs irradiated in PMMA or water by Monte Carlo simulation and experiments. Differences in the energy correction factors between rods and chips of the same thickness were negligible both in the experiments and in Monte Carlo calculation. When the diameter of the LiF TLD micro-rod was increased from 1 to 5 mm, the simulated energy correction factors increased by as much as 5% over this energy range. The energy correction factors changed by up to 4% for irradiation of TLD at depths other than at dmax for a 5 MeV mono-energetic electron beam.