title: Intra-fraction motion of the prostate during treatment with helical tomotherapy.
abstract: OBJECTIVE
  To measure the geometric uncertainty resulting from intra-fraction motion and intra-observer image matching, for patients having image-guided prostate radiotherapy on TomoTherapy.
  
  
  METHODS
  All patients had already been selected for prostate radiotherapy on TomoTherapy, with daily MV-CT imaging. The study involved performing an additional MV-CT image at the end of treatment, on 5 occasions during the course of 37 treatments. 54 patients were recruited to the study. A new formula was derived to calculate the PTV margin for intra-fraction motion.
  
  
  RESULTS
  The mean values of the intra-fraction differences were 0.0mm, 0.5mm, 0.5mm and 0.0° for LR, SI, AP and roll, respectively. The corresponding standard deviations were 1.1mm, 0.8mm, 0.8mm and 0.6° for systematic uncertainties (Σ), 1.3mm, 2.0mm, 2.2mm and 0.3° for random uncertainties (σ). This intra-fraction motion requires margins of 2.2mm in LR, 2.1mm in SI and 2.1mm in AP directions. Inclusion of estimates of the effect of rotations and matching errors increases these margins to approximately 4mm in LR and 5mm in SI and AP directions.
  
  
  CONCLUSIONS
  A new margin recipe has been developed to calculate margins for intra-fraction motion. This recipe is applicable to any measurement technique that is based on the difference between images taken before and after treatment.
authors.affiliation: Department of Medical Physics, Addenbrooke's Hospital, Cambridge, UK. Electronic address: simon.thomas@addenbrookes.nhs.uk.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Thomas
authors.forename: Mark
authors.initials: M
authors.lastname: Ashburner
authors.forename: George Samuel J
authors.initials: GS
authors.lastname: Tudor
authors.forename: Jo
authors.initials: J
authors.lastname: Treeby
authors.forename: June
authors.initials: J
authors.lastname: Dean
authors.forename: Donna
authors.initials: D
authors.lastname: Routsis
authors.forename: Yvonne L
authors.initials: YL
authors.lastname: Rimmer
authors.forename: Simon G
authors.initials: SG
authors.lastname: Russell
authors.forename: Neil G
authors.initials: NG
authors.lastname: Burnet
mesh_terms: D006801:Humans; D008297:Male; D009038:Motion; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods
keywords: Intra-fraction; Margin recipe; Tomotherapy