Influence of the internal metallic port in breast tissue expander on the electron beam dose distribution in post mastectomy radiation therapy: a Monte Carlo study

Introduction: Tissue Expanders (TE) with Internal Metallic Port (IMP) is one of the breast reconstruction methods. Irradiation of breast cancer in the presence of TE with IMP is sometimes necessary in the event of the recurrence of breast cancer. The electron beam dose distribution can be affected by the presence of inhomogeneities such as IMP in beam path. The purpose of this study was to determine the effect of IMP on the dose distribution. Methods: The effect of IMP on the dose distribution was calculated by general purpose Monte Carlo (MC) code MCNPX for 15 MV electron beam in breast phantom. Results: MC calculations showed that the presence of IMP leaded a Percentage Depth Dose (PDD) reduction in downstream of the IMP and the variation of maximum depth dose from 4.25 cm to 2.38 cm. The relative PDD reduction compared to PDD results without IMP were in ranges from 8% to 27%. The increased PDD, approximately 15% were observed in the vicinity of IMP. Conclusion and discussion: IMP leads to secondary electron production and dose enhancement in the vicinity of IMP. Due to this variation in dose distribution, the heterogeneity corrections should be used in treatment.

Keywords:

Monte Carlo , Tissue Expanders , Internal Metallic Port