title: Daily prostate volume and position monitoring using implanted gold markers and on-board imaging during radiotherapy.
abstract: OBJECTIVE
  This study aimed to evaluate prostate volume changes and prostate motions during radiotherapy.
  
  
  METHODS
  In 2010, twenty-five patients were treated for prostate cancer by external beam radiotherapy with implanted fiducial markers. Coordinates of three gold markers on kilovoltage images were calculated daily. Volume changes in target structure were observed through changes in intermarker distances. Differences in patient position between laser-tattoo alignment and gold marker localization were evaluated. Intrafraction motion was assessed by measuring marker displacement on kilovoltage images acquired before and after fraction delivery.
  
  
  RESULTS
  Prostate shrinkage was observed in 60% of patients. The average shrinkage was 7% of the prostate's initial volume. Corrections after laser-tattoo alignment remained mostly below 1 cm. The difference between marker centroid position on the actual images and the planning images was 2 +/- 1 mm on average. The extension of intrafraction movements was 7.6 +/- 0.2 mm on average.
  
  
  CONCLUSIONS
  In our retrospective study, the possibility for prostate volume changes during radiotherapy was revealed. Intrafraction movements turned out to be the limiting factor in safety margin reduction.
authors.affiliation: Department of Oncology and Radiotherapy, Charles University in Prague, Faculty of Medicine and University Hospital Hradec Králové, Czech Republic. kasaova@fnhk.cz
authors.forename: Linda
authors.initials: L
authors.lastname: Kasaová
authors.forename: Igor
authors.initials: I
authors.lastname: Sirák
authors.forename: Jan
authors.initials: J
authors.lastname: Jansa
authors.forename: Petr
authors.initials: P
authors.lastname: Paluska
authors.forename: Jirí
authors.initials: J
authors.lastname: Petera
mesh_terms: D057918:Fiducial Markers; D006046:Gold; D006801:Humans; D008297:Male; D009929:Organ Size / Q000528:radiation effects; D056888:Patient Positioning; D011467:Prostate / Q000000981:diagnostic imaging / Q000473:pathology* / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed
chemical_list: D006046:Gold