title: Impact of heterogeneity-corrected dose calculation using a grid-based Boltzmann solver on breast and cervix cancer brachytherapy.
abstract: OBJECTIVE
  To analyze the impact of heterogeneity-corrected dose calculation on dosimetric quality parameters in gynecological and breast brachytherapy using Acuros, a grid-based Boltzmann equation solver (GBBS), and to evaluate the shielding effects of different cervix brachytherapy applicators.
  
  
  METHODS
  Calculations with TG-43 and Acuros were based on computed tomography (CT) retrospectively, for 10 cases of accelerated partial breast irradiation and 9 cervix cancer cases treated with tandem-ring applicators. Phantom CT-scans of different applicators (plastic and titanium) were acquired. For breast cases the V20Gyαβ3 to lung, the D0.1cm(3) , D1cm(3) , D2cm(3) to rib, the D0.1cm(3) , D1cm(3) , D10cm(3) to skin, and Dmax for all structures were reported. For cervix cases, the D0.1cm(3) , D2cm(3) to bladder, rectum and sigmoid, and the D50, D90, D98, V100 for the CTVHR were reported. For the phantom study, surrogates for target and organ at risk were created for a similar dose volume histogram (DVH) analysis. Absorbed dose and equivalent dose to 2 Gy fractionation (EQD2) were used for comparison.
  
  
  RESULTS
  Calculations with TG-43 overestimated the dose for all dosimetric indices investigated. For breast, a decrease of ~8% was found for D10cm(3) to the skin and 5% for D2cm(3) to rib, resulting in a difference ~ -1.5 Gy EQD2 for overall treatment. Smaller effects were found for cervix cases with the plastic applicator, with up to -2% (-0.2 Gy EQD2) per fraction for organs at risk and -0.5% (-0.3 Gy EQD2) per fraction for CTVHR. The shielding effect of the titanium applicator resulted in a decrease of 2% for D2cm(3) to the organ at risk versus 0.7% for plastic.
  
  
  CONCLUSIONS
  Lower doses were reported when calculating with Acuros compared to TG-43. Differences in dose parameters were larger in breast cases. A lower impact on clinical dose parameters was found for the cervix cases. Applicator material causes systematic shielding effects that can be taken into account.
authors.affiliation: Institut für Krankenhausphysik, Krankenhaus Hietzing, Vienna, Austria; Department of Radiotherapy, Comprehensive Cancer Center, Medical University of Vienna, Austria.
authors.forename: Julia
authors.initials: J
authors.lastname: Hofbauer
authors.affiliation: Department of Radiotherapy, Comprehensive Cancer Center, Medical University of Vienna, Austria; Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Kirisits
authors.affiliation: Department of Radiotherapy, Comprehensive Cancer Center, Medical University of Vienna, Austria.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Resch
authors.affiliation: Department of Radiation Oncology, Chinese Academy of Medical Sciences, Beijing, China.
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Radiotherapy, Comprehensive Cancer Center, Medical University of Vienna, Austria.
authors.forename: Alina
authors.initials: A
authors.lastname: Sturdza
authors.affiliation: Department of Radiotherapy, Comprehensive Cancer Center, Medical University of Vienna, Austria; Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Austria.
authors.forename: Richard
authors.initials: R
authors.lastname: Pötter
authors.affiliation: Department of Radiotherapy, Comprehensive Cancer Center, Medical University of Vienna, Austria; Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Austria.
authors.forename: Nicole
authors.initials: N
authors.lastname: Nesvacil
keywords: Acuros; brachytherapy; breast; cervix; dose calculation