title: Intrafraction prostate translations and rotations during hypofractionated robotic radiation surgery: dosimetric impact of correction strategies and margins.
abstract: OBJECTIVE
  To investigate the dosimetric impact of intrafraction prostate motion and the effect of robot correction strategies for hypofractionated CyberKnife treatments with a simultaneously integrated boost.
  
  
  METHODS
  A total of 548 real-time prostate motion tracks from 17 patients were available for dosimetric simulations of CyberKnife treatments, in which various correction strategies were included. Fixed time intervals between imaging/correction (15, 60, 180, and 360 seconds) were simulated, as well as adaptive timing (ie, the time interval reduced from 60 to 15 seconds in case prostate motion exceeded 3 mm or 2° in consecutive images). The simulated extent of robot corrections was also varied: no corrections, translational corrections only, and translational corrections combined with rotational corrections up to 5°, 10°, and perfect rotational correction. The correction strategies were evaluated for treatment plans with a 0-mm or 3-mm margin around the clinical target volume (CTV). We recorded CTV coverage (V100%) and dose-volume parameters of the peripheral zone (boost), rectum, bladder, and urethra.
  
  
  RESULTS
  Planned dose parameters were increasingly preserved with larger extents of robot corrections. A time interval between corrections of 60 to 180 seconds provided optimal preservation of CTV coverage. To achieve 98% CTV coverage in 98% of the treatments, translational and rotational corrections up to 10° were required for the 0-mm margin plans, whereas translational and rotational corrections up to 5° were required for the 3-mm margin plans. Rectum and bladder were spared considerably better in the 0-mm margin plans. Adaptive timing did not improve delivered dose.
  
  
  CONCLUSIONS
  Intrafraction prostate motion substantially affected the delivered dose but was compensated for effectively by robot corrections using a time interval of 60 to 180 seconds. A 0-mm margin required larger extents of additional rotational corrections than a 3-mm margin but resulted in lower doses to rectum and bladder.
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands. Electronic address: s.vandewater@erasmusmc.nl.
authors.forename: Steven
authors.initials: S
authors.lastname: van de Water
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands; Alma Mater Studiorum, Department of Physics and Astronomy, Bologna University, Bologna, Italy.
authors.forename: Lorella
authors.initials: L
authors.lastname: Valli
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands.
authors.forename: Shafak
authors.initials: S
authors.lastname: Aluwini
authors.affiliation: Alma Mater Studiorum, Department of Physics and Astronomy, Bologna University, Bologna, Italy.
authors.forename: Nico
authors.initials: N
authors.lastname: Lanconelli
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands.
authors.forename: Ben
authors.initials: B
authors.lastname: Heijmen
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands.
authors.forename: Mischa
authors.initials: M
authors.lastname: Hoogeman
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D019583:Dose Fractionation, Radiation; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008297:Male; D009068:Movement; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000532:radiotherapy* / Q000601:surgery*; D011874:Radiometry / Q000379:methods*; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum / Q000528:radiation effects; D012371:Robotics; D013997:Time Factors; D001743:Urinary Bladder / Q000528:radiation effects