Impact of transverse magnetic fields on dose response of a nanoDot OSLD in megavoltage photon beams.

PURPOSE

We investigated the impact of transverse magnetic fields on the dose response of a nanoDot optically stimulated luminescence dosimetry (OSLD) in megavoltage photon beams.

METHODS

The nanoDot OSLD response was calculated via Monte Carlo (MC) simulations. The responses R and R without and with the transverse magnetic fields of 0.35-3 T were analyzed as a function of depth at a 10 cm × 10 cm field for 4-18 MV photons in a solid water phantom. All responses were determined based on comparisons with the response under the reference conditions (depth of 10 cm and a 10 cm × 10 cm field) for 6 MV without the magnetic field. In addition, the influence of air-gaps on the nanoDot response in the magnetic field was estimated according to Burlin's general cavity theory.

RESULTS

The R as a function of depth for 4-18 MV ranged from 1.013 to 0.993, excepting the buildup region. The R increased from 2.8% to 1.5% at 1.5 T and decreased from 3.0% to 1.1% at 3 T in comparison with R as the photon energy increased. The depth dependence of R was less than 1%, excepting the buildup region. The top air-gap and the bottom air- gap were responsible for the response reduction and the response increase, respectively.

CONCLUSIONS

The response R varied depending on the magnetic field intensity, and the variation of R reduced as the photon beam energy increased. The air-gaps affected the dose deposition in the magnetic fields.