title: Dosimetric benefits of robust treatment planning for intensity modulated proton therapy for base-of-skull cancers.
abstract: OBJECTIVE
  The clinical advantage of intensity modulated proton therapy (IMPT) may be diminished by range and patient setup uncertainties. We evaluated the effectiveness of robust optimization that incorporates uncertainties into the treatment planning optimization algorithm for treatment of base of skull cancers.
  
  
  METHODS
  We compared 2 IMPT planning methods for 10 patients with base of skull chordomas and chondrosarcomas: (1) conventional optimization, in which uncertainties are dealt with by creating a planning target volume (PTV); and (2) robust optimization, in which uncertainties are dealt with by optimizing individual spot weights without a PTV. We calculated root-mean-square deviation doses (RMSDs) for every voxel to generate RMSD volume histograms (RVHs). The area under the RVH curve was used for relative comparison of the 2 methods' plan robustness. Potential benefits of robust planning, in terms of target dose coverage and homogeneity and sparing of organs at risk (OARs) were evaluated using established clinical metrics. Then the plan evaluation metrics were averaged and compared with 2-sided paired t tests. The impact of tumor volume on the effectiveness of robust optimization was also analyzed.
  
  
  RESULTS
  Relative to conventionally optimized plans, robustly optimized plans were less sensitive for both targets and OARs. In the nominal scenario, robust and conventional optimization resulted in similar D95% doses (D95% clinical target volume [CTV]: 63.3 and 64.8 Gy relative biologic effectiveness [RBE]), P <.01]) and D5%-D95% (D5%-D95% CTV: 8.0 and 7.1 Gy[RBE], [P <.01); irradiation of OARs was less with robust optimization (brainstem V60: 0.076 vs 0.26 cm(3) [P <.01], left temporal lobe V70: 0.22 vs 0.41 cm(3), [P = .068], right temporal lobe V70: 0.016 vs 0.11 cm(3), [P = .096], left cochlea Dmean: 28.1 vs 30.1 Gy[RBE], [P = .023], right cochlea Dmean: 23.7 vs 25.2 Gy[RBE], [P = .059]). Results in the worst-case scenario were analogous.
  
  
  CONCLUSIONS
  Robust optimization is effective for creating clinically feasible IMPT plans for tumors of the base of skull.
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona. Electronic address: Liu.Wei@mayo.edu.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.affiliation: Department of Radiation Oncology, Emory University, Atlanta, Georgia.
authors.forename: Peter
authors.initials: P
authors.lastname: Park
authors.affiliation: School of Business Administration, Southwestern University of Finance and Economics, Chengdu, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Heng
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Xiaoqiang
authors.initials: X
authors.lastname: Li
authors.affiliation: Varian Medical Systems, Inc, Palo Alto, California.
authors.forename: Yupeng
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Richard
authors.initials: R
authors.lastname: Wu
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Narayan
authors.initials: N
authors.lastname: Sahoo
authors.affiliation: Scripps Proton Center, San Diego, California.
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: X Ronald
authors.initials: XR
authors.lastname: Zhu
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: David R
authors.initials: DR
authors.lastname: Grosshans
mesh_terms: D000465:Algorithms; D002813:Chondrosarcoma / Q000532:radiotherapy*; D002817:Chordoma / Q000532:radiotherapy*; D006801:Humans; D061766:Proton Therapy / Q000379:methods*; D011874:Radiometry / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012189:Retrospective Studies; D019292:Skull Base Neoplasms / Q000532:radiotherapy*