Room: Exhibit Hall | Forum 1
Purpose: To investigate the impact of transverse magnetic fields on the dose response of a commercial optically stimulated luminescent dosimeter (OSLD) for megavoltage x-ray beams.
Methods: A nanoDot OSLD was modeled using the EGSnrc/egs_chamber code. The nanoDot dose D(n)(a)(n)(o) was scored in the sensitive volume (Alâ‚‚Oâ‚ƒ) at a depth of maximum dose (d(m)(a)(x)) and depths of 5, 10 15, 20, and 25 cm in a solid water phantom at a source-axis-distance of 100 cm. The irradiation in transverse magnetic fields of 0, 0.35, 1, 1.5, and 3 T were set to a 10 Ã— 10 cmÂ² field for beam qualities Q of 4, 6, 10, and 18 MV photons. The dose to solid water D(s)(w) was also scored at the same point as the nanoDot. The nanoDot responses R(Q) and R(Q)(,)(B) without and with magnetic fields, respectively, were calculated from the ratio of (D(s)(w)/D(n)(a)(n)(o)) for 6 MV to Q. In addition, the influence of air-gaps on the nanDot response in the magnetic field was investigated by the Monte Carlo method.
Results: The R(Q)(,)(B) varied depending on magnetic field strengths and it was 2.5% higher for 1.5T and 3% lower for 3 T than for 0 T. The R(Q)(,)(B) reduced from 2.5% to 1.5% at 1.5 T and from 3% to 1% at 3 T in comparison with R(Q) as the photon beam energy increases. The nanoDot response was independent of depth excepting d(m)(a)(x). The air-gap located above the sensitive volume of nanoDot was responsible for the response reduction. In contract, the air-gap at the bottom was responsible for the response increase.
Conclusion: The nanoDot response for megavoltage x-ray beams was less than 2% without the magnetic field but it varied by 6% depending on transvers magnetic field strengths and the beam quality.