title: Influence of interfraction motion on margins for radiotherapy of gastric cancer.
abstract: OBJECTIVE
  The aim of this study was to evaluate interfraction uncertainties using kilovoltage (kV) radiographs for patients with gastric cancer during chemoradiotherapy and to calculate the planning target volume (PTV) margins.
  
  
  METHODS
  1284 measurements of set-up errors were analysed for treated patients. The measurements of craniocaudal (axis y), laterolateral (axis x) and anteroposterior (axis z) shifts in kV radiographs were performed. Interfraction clinical target volume (CTV)-PTV margins for all directions were calculated using the van Herk formula.
  
  
  RESULTS
  The main shift for the y-axis was 0.7 mm [standard deviation (SD), ±7.6], for the x-axis was 0.4 mm (SD, ±3.7) and for the z-axis was 0.6 mm (SD, ±3.5). The CTV-PTV margin in the x, y and z directions was 8.3, 15.5 and 8.0 mm, respectively. We observed that the interfractional motion for patients increased approximately 0.0034 cm along the x direction with each subsequent fraction, whereas a 0.0058-cm reduction in length along the y-axis was observed. No time effects for the z direction were noticed.
  
  
  CONCLUSIONS
  According to our experience, a PTV margin of 9 mm along the x-axis, 16 mm along the y-axis and 8 mm along the z direction should be considered in the absence of image-guided radiotherapy.
  
  
  CONCLUSIONS
  This knowledge concerning PTV set-up margins could be particularly useful for centres without a kV on-board imaging system.
authors: 1 Department of Radiotherapy, Maria Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice, Poland.
authors: A
authors: A
authors: Namysł-Kaletka
authors: J
authors: J
authors: Wydmanski
authors: A
authors: A
authors: Tukiendorf
authors: D
authors: D
authors: Bodusz
authors: W
authors: W
authors: Leszczynski
authors: R
authors: R
authors: Kawczynski
authors: K
authors: K
authors: Grabinska
authors: P
authors: P
authors: Polanowski
mesh_terms: D059248:Chemoradiotherapy; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008297:Male; D009038:Motion; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D061089:Radiotherapy, Image-Guided; D013274:Stomach Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*