Dosimetric evaluation of breast radiotherapy treatments using magnetic valve expansion prostheses

Abstract

This work intends to verify the influence on the dose distribution that the expansive prosthesis (SILIMED/470), containing a magnetic valve, generates in postoperative radiotherapy treatments of patients who underwent mastectomy. The presence of this metal during radiotherapy difficulties the treatment planning stage, due to the artifacts generated by the magnet in the acquisition of computed tomography. Radiochromic films (Gafchromic EBT2) were used for planar detection inside the prosthesis, around the metal in a plastic phantom that simulates breast geometry filled with water, an insert in the center allowed the placement of the magnet and 2.5 mm thick acrylic layers for film positioning above and below the metal at different depths. The phantom was irradiated with a 3D planning performed in XiO software (CMS RTP) with no heterogeneity correction, using beams of 6 MV and 15MV from the Oncor linear accelerator (Siemens) with a dose of 2Gy. The film calibration methodology was performed, and the optical densities of the films were measured using a CQ-01 digital densitometer (MRA). In the internal region of the prosthesis, for irradiation with 6MV, an unexpected dose increases of 7.6% was obtained for all films and, just above the magnet, an increase of 14.4% was noted. For the 15 MV beam, the films around the magnet had a dose increase of 10.4% considering the planning value and at 10mm away from the metal, a decrease of 1.28% of the expected dose was observed.