title: Role of image-guided patient repositioning and online planning in localized prostate cancer IMRT.
abstract: OBJECTIVE
  To determine the expected benefit of image-guided online replanning over image-guided repositioning of localized prostate cancer intensity-modulated radiotherapy (IMRT).
  
  
  METHODS
  On 10 to 11 CT scans of each of 10 early-stage prostate cancer patients, the prostate, bladder and rectum are manually segmented. Using a 3-mm PTV margin expansion from the CTV, an IMRT plan is made on the first CT scan of each patient. Online repositioning is simulated by recalculating the IMRT plan from the initial CT scan on the subsequent CT scans of each patient. For online replanning, IMRT is replanned twice on all CT scans, using 0-mm and 3-mm margins. The doses from subsequent CT images of each patient are then deformed to the initial CT anatomy using a mesh-based thin-plate B-spline deformation method and are accumulated for DVH and isodose review.
  
  
  RESULTS
  Paired t-tests show that online replanning with 3-mm margins significantly increases the prostate volume receiving the prescribed dose over replanning with 0-mm margins (p-value 0.004); gives marginally better target coverage than repositioning with 3-mm margins(p-value 0.06-0.343), and reduces variations in target coverage over repositioning. Fractional volumes of rectum and bladder receiving 75%, 80%, 85%, 90%, and 95% (V75, V80, V85, V90, and V95) of the prescription dose are evaluated. V90 and V95 values for the rectum are 1.6% and 0.7 % for 3-mm margin replanning and 1% and 0.4 % for 0-mm margin replanning, with p-values of 0.010-0.011. No significant differences between repositioning and replanning with 3-mm margins are found for both the rectum and the bladder.
  
  
  CONCLUSIONS
  Image-guided replanning using 3-mm margins reduces target coverage variations, and maintains comparable rectum and bladder sparing to patient repositioning in localized prostate cancer IMRT. Marginal reductions in doses to rectum and bladder are possible when planning margins are eliminated in the online replanning scenario. However, further reduction in treatment planning margins is not recommended.
authors: University of Maryland School of Medicine, Baltimore, MD 21201, USA. flerma@umm.edu
authors: Fritz A
authors: FA
authors: Lerma
authors: Bei
authors: B
authors: Liu
authors: Zhendong
authors: Z
authors: Wang
authors: Byongyong
authors: B
authors: Yi
authors: Pradip
authors: P
authors: Amin
authors: Sandy
authors: S
authors: Liu
authors: Yuanming
authors: Y
authors: Feng
authors: Cedric X
authors: CX
authors: Yu
mesh_terms: D006801:Humans; D008297:Male; D009367:Neoplasm Staging; D009862:Online Systems; D056888:Patient Positioning / Q000379:methods*; D016684:Prone Position; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012307:Risk Factors; D016683:Supine Position; D016896:Treatment Outcome