title: Observation of intrafraction prostate displacement through the course of conventionally fractionated radiotherapy for prostate cancer.
abstract: OBJECTIVE
  Intrafraction prostate displacement (IFPD) through the course of conventionally fractionated radiotherapy was observed by real-time tracking.
  
  
  METHODS
  IFPD was observed by using a CyberKnife real-time tracking system over 39 serial fractions in two patients. Stereoscopic X-ray images tracking the implanted fiducial markers were obtained with mean intervals of 58 s. In preparation for treatment, urination was performed routinely 1 h before treatment and rectal gas was evacuated if necessary. Patients were immobilized by a thermoplastic body shell.
  
  
  RESULTS
  The maximal absolute values of IFPD in all 78 fractions were 7.9, 2.1, and 11.5 mm in cranio-caudal (CC), left-right (LR), and antero-posterior (AP) direction, respectively. Only in 5 % of fractions (4/78 fractions), the maximal absolute values of IFPD were 5.0 mm or larger. In these fractions, large IFPD was temporary or persistent. IFPD of ≥3 mm was detected in only ~2-3 % of all obtained tracking images.
  
  
  CONCLUSIONS
  Daily maximal IFPD changed day by day. Although maximal IFPD was more than 10 mm, IFPD of ≥3 mm was observed in a comparatively small proportion of treatment time. Through the course of conventionally fractionated radiotherapy, fractions with IFPD of ≥5 mm were infrequent.
authors: Department of Radiology, Saiseikai-Imabari Hospital, 7-1-6 Kitamura, Imabari, Ehime, 799-1592, Japan, yahamamot@gmail.com.
authors: Yasushi
authors: Y
authors: Hamamoto
authors: Hiroki
authors: H
authors: Inata
authors: Noritaka
authors: N
authors: Sodeoka
authors: Shigeki
authors: S
authors: Nakayama
authors: Shintaro
authors: S
authors: Tsuruoka
authors: Hideki
authors: H
authors: Takeda
authors: Toshiharu
authors: T
authors: Manabe
authors: Teruhito
authors: T
authors: Mochizuki
authors: Masakichi
authors: M
authors: Umeda
mesh_terms: D000368:Aged; D019583:Dose Fractionation, Radiation; D057918:Fiducial Markers; D006801:Humans; D007103:Immobilization; D008297:Male; D009367:Neoplasm Staging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D065287:Robotic Surgical Procedures; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome