title: A beam-specific planning target volume (PTV) design for proton therapy to account for setup and range uncertainties.
abstract: OBJECTIVE
  To report a method for explicitly designing a planning target volume (PTV) for treatment planning and evaluation in heterogeneous media for passively scattered proton therapy and scanning beam proton therapy using single-field optimization (SFO).
  
  
  METHODS
  A beam-specific PTV (bsPTV) for proton beams was derived by ray-tracing and shifting ray lines to account for tissue misalignment in the presence of setup error or organ motion. Range uncertainties resulting from inaccuracies in computed tomography-based range estimation were calculated for proximal and distal surfaces of the target in the beam direction. The bsPTV was then constructed based on local heterogeneity. The bsPTV thus can be used directly as a planning target as if it were in photon therapy. To test the robustness of the bsPTV, we generated a single-field proton plan in a virtual phantom. Intentional setup and range errors were introduced. Dose coverage to the clinical target volume (CTV) under various simulation conditions was compared between plans designed based on the bsPTV and a conventional PTV.
  
  
  RESULTS
  The simulated treatment using the bsPTV design performed significantly better than the plan using the conventional PTV in maintaining dose coverage to the CTV. With conventional PTV plans, the minimum coverage to the CTV dropped from 99% to 67% in the presence of setup error, internal motion, and range uncertainty. However, plans using the bsPTV showed minimal drop of target coverage from 99% to 94%.
  
  
  CONCLUSIONS
  The conventional geometry-based PTV concept used in photon therapy does not work well for proton therapy. We investigated and validated a beam-specific PTV method for designing and evaluating proton plans.
authors.affiliation: Medical Physics Program, Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, TX, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Park
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: Adam D
authors.initials: AD
authors.lastname: Melancon
authors.forename: Lifei
authors.initials: L
authors.lastname: Zhang
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
mesh_terms: D000465:Algorithms; D006801:Humans; D009068:Movement; D061766:Proton Therapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors; D047368:Tumor Burden; D035501:Uncertainty; D011522:Protons
chemical_list: D011522:Protons