Effect of transverse magnetic field on dose distributions of yttrium 90 skin patch source

The total dose absorbed on the tumor cell from the skin patch sources used in clinical superficial brachytherapy should be limited within the target tumor volume in order to minimize the potential side effects. Average range of the beta particles within tissue may exceed the thickness of a superficial skin tumor beyond the target tumor volume, causing side effects by damaging the deeper located healthy tissue and the bone underneath the tumor. It is desired to minimize the possible side effects by selecting a short-range radionuclide. Administering the treatment under an external magnetic field is another option for reducing side effects. To achieve this, in this study, the percentage deep dose (PDD) and transverse dose profile (TDP) distributions of the skin patch source labeled with Yttrium 90 (90Y) using the GEANT4-based GAMOS Monte Carlo code were examined before and after applying magnetic field, and it was evaluated  whether it was possible to limit the dose within a certain volume or not. Simulation results showed that, along with the application of a transverse magnetic field, the dose values increased by 7.2% and 3.1% respectively at 0.25 mm and 1.0 mm depths whereas it decreased by 9.4%, 25.0%, 41.8% and 57.6%, at 2.0 mm, 3.0 mm, 4.0 mm and 5.0 mm depths respectively on the central axis from the surface of the tissue phantom with respect to the 0 T values of the field.  In case of a superficial skin tumor with a thickness of 3.0 mm from the skin surface, the amount of dose accumulated in the tumor volume for 0 T value of the transverse magnetic field was 89% of the total dose, while it increased to 98% at the intensity of 1.5 T, and the dose received by the healthy tissue under the tumor decreased by 10.1%.