title: [Dosimetric impact of image-guided translational isocenter correction for 3-D conformal radiotherapy of the prostate].
abstract: OBJECTIVE
  Interfractional prostate motion during radiotherapy due to variation in rectal distension can have negative consequences. The authors investigated the dosimetric consequences of a linear translational position correction based on image guidance when a three-dimensional conformal treatment technique was used.
  
  
  METHODS
  Planning CTs of seven patients with empty and distended rectum were analyzed. A reference plan for the planning target volume (PTV) and the boost were calculated on the CT dataset with the empty rectum with a standard four-field technique. The treatment plan was transferred to the CT with the distended rectum for an uncorrected setup (referenced to bony anatomy) and a corrected setup after position correction of the isocenter. The dosimetric consequences were analyzed.
  
  
  RESULTS
  Organ motion decreased the coverage of the prostate by the 95% isodose during simulated single treatment fractions by up to -21.0 percentage points (%-p; boost plan) and by up to -14.9%-p for the seminal vesicles (PTV plan). The mean rectum dose increased by up to 18.3%-p (PTV plan). Linear translational correction (mean 6.4 +/- 3.4 mm, maximum 10.8 mm) increased the coverage of the prostate by the 95% isodose by up to 12.7%-p (boost plan), while the mean rectum dose was reduced by up to -8.9%-p (PTV plan). For the complete treatment a reduction of complication probability of the rectum of approximately 5%-p was calculated.
  
  
  CONCLUSIONS
  The use of an image guidance system with linear translational correction can improve radiation treatment accuracy for prostate cancer, if geometric changes are within certain limits.
authors.affiliation: Klinik für Strahlentherapie und Radioonkologie, Universitätsklinikum Mannheim, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Deutschland. hansjoerg.wertz@radonk.ma.uni-heidelberg.de
authors.forename: Hansjoerg
authors.initials: H
authors.lastname: Wertz
authors.forename: Frank
authors.initials: F
authors.lastname: Lohr
authors.forename: Barbara
authors.initials: B
authors.lastname: Dobler
authors.forename: Sabine
authors.initials: S
authors.lastname: Mai
authors.forename: Frederik
authors.initials: F
authors.lastname: Wenz
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed