title: Modifying the planning target volume to optimize the dose distribution in dynamic conformal arc therapy for large metastatic brain tumors.
abstract: OBJECTIVE
  When treating large metastatic brain tumors with stereotactic radiotherapy (SRT), high dose conformity to target is difficult to achieve. Employing a modified planning target volume (mPTV) instead of the original PTV may be one way to improve the dose distribution in linear accelerator-based SRT using a dynamic conformal technique. In this study, we quantitatively analyzed the impact of a mPTV on dose distribution.
  
  
  METHODS
  Twenty-four tumors with a maximum diameter of >2 cm were collected. For each tumor, two plans were created: one used a mPTV and the other did not. The mPTV was produced by shrinking or enlarging the original PTV according to the dose distribution in the original plan. The dose conformity was evaluated and compared between the plans using a two-sided paired t test.
  
  
  RESULTS
  The conformity index defined by the Radiation Therapy Oncology Group was 1.34 ± 0.10 and 1.41 ± 0.13, and Paddick's conformity index was 0.75 ± 0.05 and 0.71 ± 0.06, for the plans with and without a mPTV, respectively. All of these improvements were statistically significant (P < 0.05).
  
  
  CONCLUSIONS
  The use of a mPTV can improve target conformity when planning SRT for large metastatic brain tumors.
authors.affiliation: Department of Radiation Oncology, Kobe City Medical Center General Hospital, 2-1-1 Minatojima-Minamimachi Chuo-ku, Kobe, 6500047, Japan. oguken@kuhp.kyoto-u.ac.jp.
authors.forename: Kengo
authors.initials: K
authors.lastname: Ogura
authors.affiliation: Department of Radiation Oncology, Kobe City Medical Center General Hospital, 2-1-1 Minatojima-Minamimachi Chuo-ku, Kobe, 6500047, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kosaka
authors.affiliation: Department of Radiation Oncology, Kobe City Medical Center General Hospital, 2-1-1 Minatojima-Minamimachi Chuo-ku, Kobe, 6500047, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Imagumbai
authors.affiliation: Department of Radiation Oncology, Kobe City Medical Center General Hospital, 2-1-1 Minatojima-Minamimachi Chuo-ku, Kobe, 6500047, Japan.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Ueki
authors.affiliation: Department of Radiation Oncology, Kobe City Medical Center General Hospital, 2-1-1 Minatojima-Minamimachi Chuo-ku, Kobe, 6500047, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Narukami
authors.affiliation: Department of Radiation Oncology, Kobe City Medical Center General Hospital, 2-1-1 Minatojima-Minamimachi Chuo-ku, Kobe, 6500047, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Hattori
authors.affiliation: Department of Radiation Oncology, Kobe City Medical Center General Hospital, 2-1-1 Minatojima-Minamimachi Chuo-ku, Kobe, 6500047, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Kokubo
mesh_terms: D001932:Brain Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D006801:Humans; D008279:Magnetic Resonance Imaging; D009362:Neoplasm Metastasis; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D014057:Tomography, X-Ray Computed
keywords: Dynamic conformal arc radiotherapy; Metastatic brain tumors; Modified planning target volume (mPTV); Stereotactic radiotherapy (SRT)