title: Balloon-based adjuvant radiotherapy in breast cancer: comparison between (99m)Tc and HDR (192)Ir.
abstract: OBJECTIVE
  To perform a comparative dosimetric analysis, based on computer simulations, of temporary balloon implants with (99m)Tc and balloon brachytherapy with high-dose-rate (HDR) (192)Ir, as boosts to radiotherapy. We hypothesized that the two techniques would produce equivalent doses under pre-established conditions of activity and exposure time.
  
  
  METHODS
  Simulations of implants with (99m)Tc-filled and HDR (192)Ir-filled balloons were performed with the Siscodes/MCNP5, modeling in voxels a magnetic resonance imaging set related to a young female. Spatial dose rate distributions were determined. In the dosimetric analysis of the protocols, the exposure time and the level of activity required were specified.
  
  
  RESULTS
  The (99m)Tc balloon presented a weighted dose rate in the tumor bed of 0.428 cGy.h(-1).mCi(-1) and 0.190 cGyh(-1).mCi(-1) at the balloon surface and at 8-10 mm from the surface, respectively, compared with 0.499 and 0.150 cGyh(-1).mCi(-1), respectively, for the HDR (192)Ir balloon. An exposure time of 24 hours was required for the (99m)Tc balloon to produce a boost of 10.14 Gy with 1.0 Ci, whereas only 24 minutes with 10.0 Ci segments were required for the HDR (192)Ir balloon to produce a boost of 5.14 Gy at the same reference point, or 10.28 Gy in two 24-minutes fractions.
  
  
  CONCLUSIONS
  Temporary (99m)Tc balloon implantation is an attractive option for adjuvant radiotherapy in breast cancer, because of its availability, economic viability, and similar dosimetry in comparison with the use of HDR (192)Ir balloon implantation, which is the current standard in clinical practice.
authors.affiliation: Postdoctoral Fellow, Professor in the Department of Nuclear Engineering, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: Tarcísio Passos Ribeiro
authors.initials: TP
authors.lastname: de Campos
authors.affiliation: MD, Nuclear Medicine Physician, Doctoral Student in the Graduate Program in Nuclear Sciences and Techniques, Núcleo de Radiações Ionizantes (NRI) at the Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: Carla Flavia
authors.initials: CF
authors.lastname: de Lima
authors.affiliation: PhD, Docent at the Center for the History of Medicine, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: Ethel Mizrahy
authors.initials: EM
authors.lastname: Cuperschmid
keywords: 192Ir; 99mTc; Balloon; Balão; Braquiterapia de mama; Breast brachytherapy; Monte Carlo method; Método Monte Carlo; Radioterapia adjuvante; Radiotherapy dosage; Radiotherapy, adjuvant; Reforço de dose