title: [Intra-fractional set-up and organ motion errors in intensity-modulated radiation therapy for prostate cancer].
abstract: OBJECTIVE
  The aim of this study is to investigate various intra-fractional errors and to determine the appropriate planning target volume (PTV) margins in intensity modulated radiation therapy (IMRT) for prostate cancer.
  
  
  METHODS
  Ten patients with prostate cancer treated with IMRT between July 2009 and March 2010 were analyzed. PTV was created by adding 4 mm posterior and 7 mm anterior and lateral margins to the clinical target volume (CTV) including prostate and proximal seminal vesicles. Intra-fractional set-up and organ motion errors were measured using cone beam computed tomography (CBCT) images before and after each irradiation. Systematic and random errors were calculated by van Herk and Stroom's models.
  
  
  RESULTS
  Intra-fractional errors of set-up and organ motion were 0.70 ± 0.84 mm and 0.88 ± 0.95 mm in the left-right (L-R), 1.04 ± 0.98 mm and 1.69 ± 1.58 mm in the cranial-coudal (C-C), and 1.08 ± 1.01 mm and 1.91 ± 1.58 mm in the anterior-posterior (A-P) directions, respectively. The errors in the C-C and A-P were significantly larger than those in the L-R (p<0.01). The organ motion errors in the C-C and A-P were significantly larger than the set-up errors (p<0.01). The appropriate PTV margin estimated in this study was 4.73 mm.
  
  
  CONCLUSIONS
  Intra-fractional errors in all directions were less than 2 mm and required PTV margin in the study was similar to actual posterior margin in our routine practice. It is important to determine intra-fractional errors as well as inter-fractional errors to deliver successful IMRT for prostate cancers.
authors.affiliation: Department of Radiology, Gunma University Hospital.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kurosawa
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Hoshino
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Higuchi
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Ogano
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Kawamura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kato
authors.forename: Hidenori
authors.initials: H
authors.lastname: Otake
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakano
mesh_terms: D000368:Aged; D054893:Cone-Beam Computed Tomography; D006801:Humans; D007103:Immobilization; D008297:Male; D008875:Middle Aged; D009038:Motion; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*