title: Prostate motion and isocenter adjustment from ultrasound-based localization during delivery of radiation therapy.
abstract: OBJECTIVE
  To study prostate motion from 4,154 ultrasound alignment fractions on 130 prostate patients treated with conformal radiotherapy or intensity-modulated radiation therapy at the University of Nebraska Medical Center.
  
  
  METHODS
  Each prostate patient was immobilized in a vacuum cradle. Daily treatment was verified by ultrasound scan after laser setup with skin marks and before radiation delivery by the same physician responsible for anatomic delineation during planning. Directional statistics were employed to test the significance of shift directions.
  
  
  RESULTS
  Polar histograms showed the prevalence of prostate motion in superior-posterior directions. The average direction was about 27 degrees from the superior axis. The average changes of prostate position in superior to inferior (SI), anterior-posterior (AP), and left to right (LR) directions and in radial distance were 0.25, -0.13, 0.03, and 0.92, cm respectively. Our data indicated that prostate motion was not patient specific, and its average magnitude remained virtually unchanged over time. Recommended planning target volume (PTV) margins for use without ultrasound localization were 0.90 cm in SI, 1.02 cm in AP, and 0.80 cm in LR directions.
  
  
  CONCLUSIONS
  Ultrasound localization revealed a predominance of prostate shift from planning position in the superior-posterior direction, with an average closer to the superior axis. The motion data provides recommended margins for PTV.
authors.affiliation: Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, NE 68198, USA. afung@unmc.edu
authors.forename: Albert Y C
authors.initials: AY
authors.lastname: Fung
authors.forename: Charles A
authors.initials: CA
authors.lastname: Enke
authors.forename: Komanduri M
authors.initials: KM
authors.lastname: Ayyangar
authors.forename: Natarajan V
authors.initials: NV
authors.lastname: Raman
authors.forename: Weining
authors.initials: W
authors.lastname: Zhen
authors.forename: Robert B
authors.initials: RB
authors.lastname: Thompson
authors.forename: Sicong
authors.initials: S
authors.lastname: Li
authors.forename: Ramasamy M
authors.initials: RM
authors.lastname: Nehru
authors.forename: Sushakumari
authors.initials: S
authors.lastname: Pillai
mesh_terms: D000465:Algorithms; D006801:Humans; D008297:Male; D009068:Movement; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal; D014463:Ultrasonography