title: Impact of heterogeneity-based dose calculation using a deterministic grid-based Boltzmann equation solver for intracavitary brachytherapy.
abstract: OBJECTIVE
  To investigate the dosimetric impact of the heterogeneity dose calculation Acuros (Transpire Inc., Gig Harbor, WA), a grid-based Boltzmann equation solver (GBBS), for brachytherapy in a cohort of cervical cancer patients.
  
  
  METHODS
  The impact of heterogeneities was retrospectively assessed in treatment plans for 26 patients who had previously received (192)Ir intracavitary brachytherapy for cervical cancer with computed tomography (CT)/magnetic resonance-compatible tandems and unshielded colpostats. The GBBS models sources, patient boundaries, applicators, and tissue heterogeneities. Multiple GBBS calculations were performed with and without solid model applicator, with and without overriding the patient contour to 1 g/cm(3) muscle, and with and without overriding contrast materials to muscle or 2.25 g/cm(3) bone. Impact of source and boundary modeling, applicator, tissue heterogeneities, and sensitivity of CT-to-material mapping of contrast were derived from the multiple calculations. American Association of Physicists in Medicine Task Group 43 (TG-43) guidelines and the GBBS were compared for the following clinical dosimetric parameters: Manchester points A and B, International Commission on Radiation Units and Measurements (ICRU) report 38 rectal and bladder points, three and nine o'clock, and (D2cm3) to the bladder, rectum, and sigmoid.
  
  
  RESULTS
  Points A and B, D(2) cm(3) bladder, ICRU bladder, and three and nine o'clock were within 5% of TG-43 for all GBBS calculations. The source and boundary and applicator account for most of the differences between the GBBS and TG-43 guidelines. The D(2cm3) rectum (n = 3), D(2cm3) sigmoid (n = 1), and ICRU rectum (n = 6) had differences of >5% from TG-43 for the worst case incorrect mapping of contrast to bone. Clinical dosimetric parameters were within 5% of TG-43 when rectal and balloon contrast were mapped to bone and radiopaque packing was not overridden.
  
  
  CONCLUSIONS
  The GBBS has minimal impact on clinical parameters for this cohort of patients with unshielded applicators. The incorrect mapping of rectal and balloon contrast does not have a significant impact on clinical parameters. Rectal parameters may be sensitive to the mapping of radiopaque packing.
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Justin K
authors.initials: JK
authors.lastname: Mikell
authors.forename: Ann H
authors.initials: AH
authors.lastname: Klopp
authors.forename: Graciela M N
authors.initials: GM
authors.lastname: Gonzalez
authors.forename: Kelly D
authors.initials: KD
authors.lastname: Kisling
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Price
authors.forename: Paula A
authors.initials: PA
authors.lastname: Berner
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Eifel
authors.forename: Firas
authors.initials: F
authors.lastname: Mourtada
mesh_terms: D001842:Bone and Bones / Q000000981:diagnostic imaging; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D015331:Cohort Studies; D012809:Colon, Sigmoid / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D009132:Muscles / Q000000981:diagnostic imaging; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D012984:Software; D001743:Urinary Bladder / Q000000981:diagnostic imaging; D014546:Urinary Catheterization / Q000295:instrumentation; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*
chemical_list: D007496:Iridium Radioisotopes