title: Impact of respiratory motion on worst-case scenario optimized intensity modulated proton therapy for lung cancers.
abstract: OBJECTIVE
  We compared conventionally optimized intensity modulated proton therapy (IMPT) treatment plans against worst-case scenario optimized treatment plans for lung cancer. The comparison of the 2 IMPT optimization strategies focused on the resulting plans' ability to retain dose objectives under the influence of patient setup, inherent proton range uncertainty, and dose perturbation caused by respiratory motion.
  
  
  METHODS
  For each of the 9 lung cancer cases, 2 treatment plans were created that accounted for treatment uncertainties in 2 different ways. The first used the conventional method: delivery of prescribed dose to the planning target volume that is geometrically expanded from the internal target volume (ITV). The second used a worst-case scenario optimization scheme that addressed setup and range uncertainties through beamlet optimization. The plan optimality and plan robustness were calculated and compared. Furthermore, the effects on dose distributions of changes in patient anatomy attributable to respiratory motion were investigated for both strategies by comparing the corresponding plan evaluation metrics at the end-inspiration and end-expiration phase and absolute differences between these phases. The mean plan evaluation metrics of the 2 groups were compared with 2-sided paired Student t tests.
  
  
  RESULTS
  Without respiratory motion considered, we affirmed that worst-case scenario optimization is superior to planning target volume-based conventional optimization in terms of plan robustness and optimality. With respiratory motion considered, worst-case scenario optimization still achieved more robust dose distributions to respiratory motion for targets and comparable or even better plan optimality (D95% ITV, 96.6% vs 96.1% [P = .26]; D5%- D95% ITV, 10.0% vs 12.3% [P = .082]; D1% spinal cord, 31.8% vs 36.5% [P = .035]).
  
  
  CONCLUSIONS
  Worst-case scenario optimization led to superior solutions for lung IMPT. Despite the fact that worst-case scenario optimization did not explicitly account for respiratory motion, it produced motion-resistant treatment plans. However, further research is needed to incorporate respiratory motion into IMPT robust optimization.
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona; Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas. Electronic address: Liu.Wei@mayo.edu.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.affiliation: Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: Steven E
authors.initials: SE
authors.lastname: Schild
authors.affiliation: School of Business Administration, Southwestern University of Finance and Economics, Chengdu, Sichuan, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Heng
authors.initials: H
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 Oncology, Emory University, Atlanta, Georgia.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Park
authors.affiliation: Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Xiaoqiang
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: Joshua
authors.initials: J
authors.lastname: Stoker
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: Jiajian
authors.initials: J
authors.lastname: Shen
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: Sameer
authors.initials: S
authors.lastname: Keole
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: Aman
authors.initials: A
authors.lastname: Anand
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: Mirek
authors.initials: M
authors.lastname: Fatyga
authors.affiliation: Scripps Proton Center, San Diego, California.
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.affiliation: Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Narayan
authors.initials: N
authors.lastname: Sahoo
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: Sujay
authors.initials: S
authors.lastname: Vora
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: William
authors.initials: W
authors.lastname: Wong
authors.affiliation: Department of Radiation Physics, 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, Mayo Clinic Arizona, Phoenix, Arizona.
authors.forename: Martin
authors.initials: M
authors.lastname: Bues
authors.affiliation: Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
mesh_terms: D006801:Humans; D008175:Lung Neoplasms / Q000503:physiopathology* / Q000532:radiotherapy*; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015656:Respiratory Mechanics / Q000502:physiology*; D012189:Retrospective Studies