title: Statistical assessment of proton treatment plans under setup and range uncertainties.
abstract: OBJECTIVE
  To evaluate a method for quantifying the effect of setup errors and range uncertainties on dose distribution and dose-volume histogram using statistical parameters; and to assess existing planning practice in selected treatment sites under setup and range uncertainties.
  
  
  METHODS
  Twenty passively scattered proton lung cancer plans, 10 prostate, and 1 brain cancer scanning-beam proton plan(s) were analyzed. To account for the dose under uncertainties, we performed a comprehensive simulation in which the dose was recalculated 600 times per given plan under the influence of random and systematic setup errors and proton range errors. On the basis of simulation results, we determined the probability of dose variations and calculated the expected values and standard deviations of dose-volume histograms. The uncertainties in dose were spatially visualized on the planning CT as a probability map of failure to target coverage or overdose of critical structures.
  
  
  RESULTS
  The expected value of target coverage under the uncertainties was consistently lower than that of the nominal value determined from the clinical target volume coverage without setup error or range uncertainty, with a mean difference of -1.1% (-0.9% for breath-hold), -0.3%, and -2.2% for lung, prostate, and a brain cases, respectively. The organs with most sensitive dose under uncertainties were esophagus and spinal cord for lung, rectum for prostate, and brain stem for brain cancer.
  
  
  CONCLUSIONS
  A clinically feasible robustness plan analysis tool based on direct dose calculation and statistical simulation has been developed. Both the expectation value and standard deviation are useful to evaluate the impact of uncertainties. The existing proton beam planning method used in this institution seems to be adequate in terms of target coverage. However, structures that are small in volume or located near the target area showed greater sensitivity to uncertainties.
authors.affiliation: Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Park
authors.forename: Joey P
authors.initials: JP
authors.lastname: Cheung
authors.forename: X Ronald
authors.initials: XR
authors.lastname: Zhu
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Lee
authors.forename: Narayan
authors.initials: N
authors.lastname: Sahoo
authors.forename: Susan L
authors.initials: SL
authors.lastname: Tucker
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Heng
authors.initials: H
authors.lastname: Li
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.forename: Laurence E
authors.initials: LE
authors.lastname: Court
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
mesh_terms: D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D001933:Brain Stem / Q000000981:diagnostic imaging / Q000528:radiation effects; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D004947:Esophagus / Q000000981:diagnostic imaging / Q000528:radiation effects; D005240:Feasibility Studies; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D061766:Proton Therapy / Q000379:methods / Q000706:statistics & numerical data*; D011836:Radiation Tolerance; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors / Q000706:statistics & numerical data*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D012189:Retrospective Studies; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000528:radiation effects; D035501:Uncertainty