title: [Evaluation of dosimetric variance in forward intensity modulated radiotherapy of the breast based on 4D CT and 3D CT during free breathing].
abstract: OBJECTIVE
  To explore the dosimetric variance in forward intensity modulated radiotherapy (IMRT) based on 4D CT and 3D CT after breast conserving surgery.
  
  
  METHODS
  Seventeen patients after breast conserving surgery underwent 3D CT simulation scans followed by respiration-synchronized 4D CT simulation scans at free breathing state. The treatment plan constructed using the end inspiration (EI) scan was then copied and applied to the end expiration (EE), and 3D scans and dose distribution were calculated separately. Dose-volume histograms (DVHs) parameters for the CTV, PTV, ipsilateral lung and heart were evaluated and compared.
  
  
  RESULTS
  The CTV volume difference was biggest between T0 and 3D CT, and the volume difference was 4.10 cm(3). Mean dose of PTV at EE was lower than that at EI (P = 0.019), but there were no statistically significant difference between 3D and EI, EE (all P > 0.05). The homogeneity index (HI) at EI, EE, 3D plans were 0.149, 0.159 and 0.164, respectively, and a significant difference was only between EI and EE (P = 0.039). The highest conformal index (CI) was at EI phase (P < 0.05), and there was no significant difference between EE and 3D (P = 0.758). The V(40) and V(50) of ipsilateral lung at EE phase were lower than that at EI (P < 0.05). There were no significant differences in all the indexes for heart (P > 0.05).
  
  
  CONCLUSIONS
  The breast deformation during respiration may be disregarded in whole breast IMRT. PTV dose distribution is significantly changed between EI and EE phases, and the differentiation of the lung high dose area between EI and EE phases may be induced by thorax expansion. 3D treatment planning is sufficient for whole breast forward IMRT, but 4D CT scans assisted by respiratory gating ensures more precise delivery of radiation dose.
authors.affiliation: Department of Radiation Oncology, Shandong Cancer Hospital & Institute, Jinan 250117, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Jian-bin
authors.initials: JB
authors.lastname: Li
authors.forename: Hong-guang
authors.initials: HG
authors.lastname: Hu
authors.forename: Tong-hai
authors.initials: TH
authors.lastname: Liu
authors.forename: Min
authors.initials: M
authors.lastname: Xu
authors.forename: Ting-yong
authors.initials: TY
authors.lastname: Fan
authors.forename: Qian
authors.initials: Q
authors.lastname: Shao
mesh_terms: D002288:Adenocarcinoma, Mucinous / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D000328:Adult; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery; D018270:Carcinoma, Ductal, Breast / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery; D019583:Dose Fractionation, Radiation; D005260:Female; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D015412:Mastectomy, Segmental; D008875:Middle Aged; D058958:Organs at Risk; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated; D012119:Respiration