title: The effect of rib and lung heterogeneities on the computed dose to lung in Ir-192 high-dose-rate breast brachytherapy: Monte Carlo versus a treatment planning system.
abstract: OBJECTIVE
  This study investigates to what extent the dose received by lungs from a commercially available treatment planning system, Ir-192 high-dose-rate (HDR), in breast brachytherapy, is accurate, with the emphasis on tissue heterogeneities, and taking into account the presence of ribs, in dose delivery to the lung.
  
  
  METHODS
  A computed tomography (CT) scan of a breast was acquired and transferred to the 3-D treatment planning system and was also used to construct a patient-equivalent phantom. An implant involving 13 plastic catheters and 383 programmed source dwell positions were simulated, using the Monte Carlo N-Particle eXtended (MCNPX) code. The Monte Carlo calculations were compared with the corresponding commercial treatment planning system (TPS) in the form of percentage isodose and cumulative dose-volume histogram (DVH) in the breast, lungs, and ribs.
  
  
  RESULTS
  The comparison of the Monte Carlo results and the TPS calculations showed that a percentage of isodose greater than 75% in the breast, which was located rather close to the implant or away from the breast curvature surface and lung boundary, were in good agreement. TPS calculations overestimated the dose to the lung for lower isodose contours that were lying near the breast surface and the boundary of breast and lung and were relatively away from the implant.
  
  
  CONCLUSIONS
  Taking into account the ribs and entering the actual data for breasts, ribs, and lungs, revealed an average overestimation of the dose by a factor of 8% in the lung for TPS calculations. Therefore, the accuracy of the TPS results may be limited to regions near the implants where the treatment is planned, and is a more conservative approach for regions at boundaries with curvatures or tissues with a different material than that in the breast.
authors.affiliation: Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Hossein Salehi
authors.initials: HS
authors.lastname: Yazdi
authors.forename: Mojtaba
authors.initials: M
authors.lastname: Shamsaei
authors.forename: Ramin
authors.initials: R
authors.lastname: Jaberi
authors.forename: Hamid Reza
authors.initials: HR
authors.lastname: Shabani
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Allahverdi
authors.forename: Seyed Ali
authors.initials: SA
authors.lastname: Vaezzadeh
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000379:methods*; D001940:Breast / Q000528:radiation effects; D001943:Breast Neoplasms / Q000532:radiotherapy*; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D008168:Lung / Q000528:radiation effects; D008954:Models, Biological; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012272:Ribs / Q000528:radiation effects; D015898:Tomography Scanners, X-Ray Computed
chemical_list: D007496:Iridium Radioisotopes