The effect of magnetic field on Linac based Stereotactic Radiosurgery dosimetric parameters

Abstract

Objective: MR-linac machines are being developed for image-guided radiation therapy but the magnetic field of such machines could affect dose distributions. The purpose of this work was to evaluate the effect of a magnetic field on linac beam dosimetric parameters including penumbra for circular cones used in radiosurgery. Methods: Monte Carlo simulation was conducted for a linac machine with circular cones at 6 MV beam. A homogenous magnetic field of 1.5 T was applied transversely and parallel to the radiation beam. Percentage depth dose (PDD) and beam profiles in a water phantom with and without the magnetic field were calculated. Results: The results have shown that when the magnetic field is applied transversely, the PDDs in the water phantom differ in the buildup region and distant part of PDD curves. The beam profiles at three different depths are all significantly different from those without the magnetic field. The penumbra is greater when a magnetic field has been applied. Conclusion: Linear accelerator-based SRT and SRS use small circular cones. The beam penumbra for these cones can change in the presence of a magnetic field. The perturbation of dose distribution has been also observed in a patient plan due to the presence of a magnetic field. The results of this study show that dose distributions in the presence of a magnetic field must be considered for MR-guided radiotherapy treatments.

Influence and optimization strategy of the magnetic field in 1.5 T MR-linac liver stereotactic radiotherapy

“…It will worsen the target dose's inhomogeneity and increase or decrease the interfacial dose under the concurrent influence of tissue inhomogeneity and ERE [ 23 ]. This conclusion is similar to that reported by Nedaie HA et al [ 24 ]. The results also show that in the treatment plans for liver cancer, the effect of a magnetic field on OARs is more stable than that on the target area.…”