title: Assessment of planning target volume margin for a small number of vertebral metastatic lesions using image-guided intensity-modulated radiation therapy by helical tomotherapy.
abstract: OBJECTIVE
  To evaluate an appropriate planning target volume (PTV) margin in for one to three vertebral metastases using megavolt computed tomography (MVCT) images during the course of image-guided and stereotactic intensity-modulated radiotherapy (IGRT-IMRT) by use of helical tomotherapy.
  
  
  METHODS
  A total of 25 lesions in 24 patients with vertebral metastases who received IGRT-IMRT were analyzed. MVCT images were acquired before and after radiation therapy. Intra-fractional movement and PTV margin were calculated by comparing treatment planning images and these 310 MVCT images for right-left (RL), superior-inferior (SI), and anteroposterior (AP) dimensions. Five patients were treated by 35 Gy/5 fractions, 17 by 30 Gy/5 fractions, one by 25 Gy/5 fractions, and one by 60 Gy/30 fractions. A margin to compensate for these variations was calculated with the formula of vanHerk's equation.
  
  
  RESULTS
  The intra-fractional motion was 0.02 (-1.3 to 1.4) ± 0.34 mm in the RL direction, -0.09 (-1.8 to 0.28) ± 0.44 mm in the SI direction, and 0.20 (-1.8 to 1.8) ± 0.36 mm in the AP direction. The required PTV margin was 0.98 mm in the RL direction, 0.69 mm in the SI direction, and 1.26 mm in the AP direction. No patient showed a deviation greater than 2 mm.
  
  
  CONCLUSIONS
  The PTV margin in hypofractionated IGRT-IMRT, using helical tomotherapy for a few vertebral metastases, was 2 mm or less and our tentative PTV margin of 5 mm was sufficient and reducible.
authors.affiliation: Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Nishimura
authors.forename: Hideya
authors.initials: H
authors.lastname: Yamazaki
authors.forename: Kazuki
authors.initials: K
authors.lastname: Iwama
authors.forename: Tomoya
authors.initials: T
authors.lastname: Kotani
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Oota
authors.forename: Hironori
authors.initials: H
authors.lastname: Aibe
authors.forename: Satoaki
authors.initials: S
authors.lastname: Nakamura
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Ikeno
authors.forename: Ken
authors.initials: K
authors.lastname: Yoshida
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Isohashi
authors.forename: Haruumi
authors.initials: H
authors.lastname: Okabe
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013125:Spinal Neoplasms / Q000532:radiotherapy* / Q000556:secondary; D014057:Tomography, X-Ray Computed
keywords: PTV margin; Tomotherapy; image-guided IMRT; stereotactic body radiotherapy; vertebral body metastases