Purpose: To investigate the response of a radiophotoluminescent glass dosimeter (RGD) under transverse magnetic fields using Monte Carlo (MC) calculations.
Methods: The RGD was modeled using the EGSnrc/egs_chamber code. In addition, the RGD with air-gap of 0.03 cm in the holder was also modeled on the assumption of the actual measurement. The RGD was positioned to receive the Lorentz force in short and long axis direction of RGD. The photon beams with beam qualities (Q) of 4, 6, 10, and 18 MV were irradiated field size of 10Ã—10 cm2. The dose in a sensitive volume of RGD (DRGD) and dose to a SW phantom (DSW) were calculated at 10 cm depth. The RGD response for Q was calculated as was obtained from the ratio of (DSW / DRGD) for 6 MV to Q without and with magnetic fields. The perturbation correction factor, PQ, for RGD was also calculated in accordance with Burlinâ€™s general cavity theory.
Results: The RGD response as a function of beam quality was within 3% for all energies. The air-gap of 0.03 cm above RGD decreased the RGD response up to 2% in 3.0 T, having larger effect on the RGD response in stronger magnetic field. The RGD response for the Lorentz force to the short axis was also less than 1% in all magnetic fields. Contrastively, the RGD response for the Lorentz force to the long axis varied by 6%. The PQ for the Lorentz force to the short axis was almost 0.96 for all energies and magnetic field strength, although for the Lorentz force to the long axis varied from 0.96 to 1.01.
Conclusion: The variation of RGD response for the Lorentz force to the short axis was smaller than those to the long axis. The RGD response is affected by air-gap in the holder.