Dosimetric verification of MammoSite treatment plans using Monte Carlo simulations and measurements with a 2D ionization chamber array

The surgical removal of a breast tumour is often followed by postoperative irradiation of the surrounding tissue with a radioactive source (brachytherapy). When performing the MammoSite procedure, a spherical silicone balloon is inserted and filled with a NaCl solution. In a period of about five days in several sessions an iridium-192 source with high activity travels through a catheter into the balloon (afterloading) to irradiate the tumour cells remaining in the cavity. In this study, dose distributions of a MammoSite applicator are investigated based on measurements with a 2D detector array, Monte Carlo simulations and calculations with BrachyVision. The focus is set on the 2D detector array and its possible application in the verification process in 3D brachytherapy treatment planning. The measured dose distributions conform well to the doses of BrachyVision with deviations of less than 5% within the clinically relevant field range. The deviations of the measured and calculated distributions from the simulation results are below 3%. The 2D detector array allows a new verification method for MammoSite treatment plans with sufficient accuracy. Future verifications can be performed without additional Monte Carlo simulations.