title: Prostate bed motion during intensity-modulated radiotherapy treatment.
abstract: OBJECTIVE
  Conformal radiation therapy in the postprostatectomy setting requires accurate setup and localization of the prostatic fossa. In this series, we report prostate bed localization and motion characteristics, using data collected from implanted radiofrequency transponders.
  
  
  METHODS
  The Calypso four-dimensional localization system uses three implanted radiofrequency transponders for daily target localization and real-time tracking throughout a course of radiation therapy. We reviewed the localization and tracking reports for 20 patients who received ultrasonography-guided placement of Calypso transponders within the prostate bed prior to a course of intensity-modulated radiation therapy at Fox Chase Cancer Center.
  
  
  RESULTS
  At localization, prostate bed displacement relative to bony anatomy exceeded 5 mm in 9% of fractions in the anterior-posterior (A-P) direction and 21% of fractions in the superior-inferior (S-I) direction. The three-dimensional vector length from skin marks to Calypso alignment exceeded 1 cm in 24% of all 652 fractions with available setup data. During treatment, the target exceeded the 5-mm tracking limit for at least 30 sec in 11% of all fractions, generally in the A-P or S-I direction. In the A-P direction, target motion was twice as likely to move posteriorly, toward the rectum, than anteriorly. Fifteen percent of all treatments were interrupted for repositioning, and 70% of patients were repositioned at least once during their treatment course.
  
  
  CONCLUSIONS
  Set-up errors and motion of the prostatic fossa during radiotherapy are nontrivial, leading to potential undertreatment of target and excess normal tissue toxicity if not taken into account during treatment planning. Localization and real-time tracking of the prostate bed via implanted Calypso transponders can be used to improve the accuracy of plan delivery.
authors.affiliation: Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania, USA.
authors.forename: Tracy
authors.initials: T
authors.lastname: Klayton
authors.forename: Robert
authors.initials: R
authors.lastname: Price
authors.forename: Mark K
authors.initials: MK
authors.lastname: Buyyounouski
authors.forename: Mark
authors.initials: M
authors.lastname: Sobczak
authors.forename: Richard
authors.initials: R
authors.lastname: Greenberg
authors.forename: Jinsheng
authors.initials: J
authors.lastname: Li
authors.forename: Lanea
authors.initials: L
authors.lastname: Keller
authors.forename: Dennis
authors.initials: D
authors.lastname: Sopka
authors.forename: Alexander
authors.initials: A
authors.lastname: Kutikov
authors.forename: Eric M
authors.initials: EM
authors.lastname: Horwitz
mesh_terms: D000368:Aged; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D019583:Dose Fractionation, Radiation; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D009068:Movement; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy* / Q000601:surgery; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors / Q000517:prevention & control; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D016879:Salvage Therapy / Q000379:methods