title: Impact of intrafractional respiratory-induced prostate mobility on PTV size.
abstract: OBJECTIVE
  Daily image-guided radiation therapy significantly reduces setup errors, but it does not minimize intrafractional target mobility; respiratory-induced target motion is one of the reasons for this. Therefore, the main aim of this study was to evaluate the impact of respiratory-induced prostate motion on the clinical target volume (CTV) margins.
  
  
  METHODS
  The analysis comprised 50 videos stored in digital format and recorded in a group of 50 patients during image-guided radiation therapy for prostate cancer. Fluoroscopy time was 10 seconds. Respiratory motion of the prostate in the anterior-posterior and lateral direction was assessed on the basis of a fiducial marker (GoldAnchor) implanted into the prostate before the treatment planning procedure.
  
  
  RESULTS
  The average values and standard deviations of respiratory-induced prostate motion in the superior-inferior and left-right (lateral) directions were 2.6 ± 2.1 mm and 0.7 ± 0.7 mm, respectively. The CTV margins calculated according to the van Herk formula based on respiratory prostate motion were 8 mm in the superior-inferior direction and 2 mm in the lateral direction.
  
  
  CONCLUSIONS
  Respiratory-induced prostate mobility during radiotherapy is significant especially in the superior-inferior direction, and can thus induce a geographical error. This confirms the need for determining CTV margins for this type of respiratory-induced mobility.
authors.affiliation: Radiotherapy Department, Maria Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Gliwice - Poland.
authors.forename: Dawid
authors.initials: D
authors.lastname: Bodusz
authors.affiliation: Radiotherapy Department, Maria Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Gliwice - Poland.
authors.forename: Leszek
authors.initials: L
authors.lastname: Miszczyk
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D011467:Prostate; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods; D012119:Respiration