Marcapasso na radioterapia mamária: caracterização computacional das alterações dosimétricas

Abstract

Cancer is one of the leading causes of death worldwide, and breast cancer is the second most frequent type and the most common among women. Population aging and unhealthy lifestyle habits contribute to the development of cancer and cardiovascular diseases (CVD), which often make the implantation of a cardiac electronic device necessary. Thus, patients with breast cancer and an implanted pacemaker may undergo radiotherapy, which is one of the treatment modalities for breast cancer. It is well established that pacemakers contain radiation-sensitive components and, because they are composed of metallic structures, may generate radiation scattering when directly exposed to the primary treatment beam. Therefore, the present study aims to analyze the dosimetric influence of the pacemaker on dose coverage in the breast, as well as to determine the absorbed dose by the device under the scenarios investigated. The Monte Carlo code TOPAS was used to simulate a breast cancer radiotherapy scenario with tangential fields on a TrueBeam linear accelerator using a 6 MV photon beam. The TET2DICOM software was used to convert the female mesh-type anthropomorphic reference phantom (MRCP) from ICRP Publication 145 into a set of DICOM images for implementation in TOPAS. Dose–volume histograms were generated, and the main dose metrics were extracted using the 3D Slicer software. The results showed that the presence of the pacemaker has a negligible impact on dose delivery to the treatment target volume. The prescription dose, D95%, was slightly reduced from 47.64 to 47.44 Gy, while the mean absorbed dose to the breast remained unchanged. Collimating the pacemaker as a strategy to reduce the absorbed dose to the device decreased its dose from 26.04 to 1.58 Gy; however, it also reduced breast dose coverage (D95% = 17.56 Gy), making this approach of limited clinical effectiveness. Advanced techniques, such as pacemaker-sparing Volumetric Modulated Arc Therapy (VMAT), should be investigated in future studies.