title: Gold seed fiducials in analysis of linear and rotational displacement of the prostate bed.
abstract: OBJECTIVE
  This study aimed to investigate the magnitude of interfraction prostate bed motion during radiotherapy using both the implanted gold seed fiducials and the soft tissue registration and to define reasonable planning target volume (PTV) margins for different localization methods.
  
  
  METHODS
  Thirteen prostatectomized prostate cancer patients, after implanting four gold seed fiducials into their prostate bed, were imaged daily using a pretreatment cone-beam computed tomography (CBCT). Linear and the rotational prostate bed motion (PBM) was measured for 466 CBCTs.
  
  
  RESULTS
  The linear PBM mean and standard deviation values in millimeters are 0.0 ± 0.5, 0.7 ± 2.1 and 0.8 ± 1.6 in the LR, SI and AP axes, respectively. In 20% of the fractions the rotation of the prostate bed in sagittal plane exceeds ±6° and in 5% it exceeds ±10° from the position on the planning CT. In the transversal and coronal planes 1% and 2% of it exceeds ±6°. The PTV margins are 2.4, 6.5 and 6.6mm in the LR, SI and AP axes, respectively, if imaging is performed for the first three treatment fractions.
  
  
  CONCLUSIONS
  The linear PBM is largest in the SI and AP axis, whereas the rotation is largest in the sagittal plane. Bone localization during the first three treatment fractions can reduce PTV margins by 52%, 18% and 10% in the LR, SI and AP axes, respectively, whereas in daily CBCT the use of the gold seed fiducials seems profitable.
authors: Helsinki University Central Hospital, Department of Oncology, Finland. Electronic address: elisa.alander@gmail.com.
authors: Elisa
authors: E
authors: Ålander
authors: Helsinki University Central Hospital, Department of Oncology, Finland.
authors: Harri
authors: H
authors: Visapää
authors: Helsinki University Central Hospital, Department of Oncology, Finland.
authors: Mauri
authors: M
authors: Kouri
authors: Helsinki University Central Hospital, Department of Oncology, Finland.
authors: Jani
authors: J
authors: Keyriläinen
authors: Helsinki University Central Hospital, Department of Oncology, Finland.
authors: Kauko
authors: K
authors: Saarilahti
authors: Helsinki University Central Hospital, Department of Oncology, Finland.
authors: Mikko
authors: M
authors: Tenhunen
mesh_terms: D000368:Aged; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods; D057918:Fiducial Markers; D006046:Gold; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D011467:Prostate / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods
chemical_list: D006046:Gold
keywords: Gold seed fiducials; Margin; Prostate bed motion; Prostate cancer; Rotation of the prostate bed