The bolus effect of magnetic fields in superficial skin tumor brachytherapy: a simulation approach

Abstract Skin cancers have become a serious public health issue and there is a need to enhance the effectiveness of existing treatment methods and to develop new prevention and treatment therapies. In recent years, superficial brachytherapy method have been developed as an alternative to such conventional treatments as external radiotherapy and surgery for treating superficial skin tumors. Integrating a magnetic field can make the superficial skin tumor brachytherapy more effective and safer. This study investigates the effects of longitudinal and transverse magnetic fields on the dose distributions of skin patch sources labeled with radionuclides 90 Y, 188 Re, 166 Ho, and 32 P, using the GEANT4-based GAMOS Monte Carlo (MC) simulation program. The simulation results showed that the longitudinal magnetic field had no significant effect on the dose distributions of the four skin patch sources while the transverse magnetic field had a substantial impact. Acting as a bolus, the transverse magnetic field increased the dose in layers close to the surface of the tissue phantom while causing significant dose reductions in deeper layers. Compared to a transverse magnetic field of 0.0 T, the percentages of dose increase at a depth of 0.2 mm from the surface of the tissue phantom for magnetic field values of 1.0 T, 2.0 T, and 3.0 T were respectively: 90 Y (3.9%, 12.4%, 20.3%), 188 Re (2.7%, 8.9%, 15.5%), 166 Ho (2.1%, 7.4%, 13.9%), and 32 P (1.9%, 6.4%, 12.5%). On the other hand, the transverse magnetic field reduced the dose at a depth of 3.0 mm from the surface of the tissue phantom by 76.9% for 90 Y, 81.6% for 188 Re, and by 86.1% and 88% for 166 Ho and 32 P, respectively. These results indicate that the dose can be confined within the desired target volume with a transverse magnetic field of appropriate magnitude.