title: Proton therapy for prostate cancer treatment employing online image guidance and an action level threshold.
abstract: OBJECTIVE
  The ability to determine the accuracy of the final prostate position within a determined action level threshold for image-guided proton therapy is unclear.
  
  
  METHODS
  Three thousand one hundred ten images for 20 consecutive patients treated in 1 of our 3 proton prostate protocols from February to May of 2007 were analyzed. Daily kV images and patient repositioning were performed employing an action-level threshold (ALT) of > or = 2.5 mm for each beam. Isocentric orthogonal x-rays were obtained, and prostate position was defined via 3 gold markers for each patient in the 3 axes.
  
  
  RESULTS
  To achieve and confirm our action level threshold, an average of 2 x-rays sets (median 2; range, 0-4) was taken daily for each patient. Based on our ALT, we made no corrections in 8.7% (range, 0%-54%), 1 correction in 82% (41%-98%), and 2 to 3 corrections in 9% (0-27%). No patient needed 4 or more corrections. All patients were treated with a confirmed error of < 2.5 mm for every beam delivered. After all corrections, the mean and standard deviations were: anterior-posterior (z): 0.003 +/- 0.094 cm; superior-inferior (y): 0.028 +/- 0.073 cm; and right-left (x) -0.013 +/- 0.08 cm.
  
  
  CONCLUSIONS
  It is feasible to limit all final prostate positions to less than 2.5 mm employing an action level image-guided radiation therapy (IGRT) process. The residual errors after corrections were very small.
authors.affiliation: University of Florida Proton Therapy Institute, Jacksonville, FL 32206, USA. c2002@ufl.edu
authors.forename: Carlos
authors.initials: C
authors.lastname: Vargas
authors.forename: Aaron
authors.initials: A
authors.lastname: Falchook
authors.forename: Daniel
authors.initials: D
authors.lastname: Indelicato
authors.forename: Anamaria
authors.initials: A
authors.lastname: Yeung
authors.forename: Randall
authors.initials: R
authors.lastname: Henderson
authors.forename: Kenneth
authors.initials: K
authors.lastname: Olivier
authors.forename: Sameer
authors.initials: S
authors.lastname: Keole
authors.forename: Christopher
authors.initials: C
authors.lastname: Williams
authors.forename: Zuofeng
authors.initials: Z
authors.lastname: Li
authors.forename: Jatinder
authors.initials: J
authors.lastname: Palta
mesh_terms: D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009367:Neoplasm Staging; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D011882:Radiotherapy, High-Energy