Monte Carlo evaluations of the absorbed dose and quality dependence of Al2O3 in radiotherapy photon beams.

Purpose: The purpose of this work was to evaluate the absorbed dose to Al₂O₃ dosimeter at various depths of water phantom in radiotherapy photon beams by Monte Carlo simulation and evaluate the beam quality dependence. Methods: The simulations were done using EGSnrc. The cylindrical Al₂O₃ dosimeter ([uppercase_phi_synonym]4 mm×1 mm) was placed at the central axis of the water phantom ([uppercase_phi_synonym]16 cm×16 cm) at depths between 0.5 and 8 cm. The incident beams included monoenergetic photon beams ranging from 1 to 18 MeV, ⁶⁰Co γ beams, Varian 6 MV beams using phase space files based on a full simulation of the linac, and Varian beams between 4 and 24 MV using Mohan’s spectra. The absorbed dose to the dosimeter and the water at the corresponding position in the absence of the dosimeter, as well as absorbed dose ratio factor f_md, was calculated. Results: The results show that f_md depends obviously on the photon energy at the shallow depths. However, as the depth increases, the change in f_md becomes small, beyond the buildup region, the maximum discrepancy of f_md to the average value is not more than 1%. Conclusions: These simulation results confirm the use of Al₂O₃ dosimeter in radiotherapy photon beams and clearly indicate that more attention should be paid when using such a dosimeter in the buildup region of high-energy radiotherapy photon beams. [ABSTRACT FROM AUTHOR]