title: Robust optimization in intensity-modulated proton therapy to account for anatomy changes in lung cancer patients.
abstract: OBJECTIVE
  Robust optimization for IMPT takes setup and range uncertainties into account during plan optimization. However, anatomical changes were not prospectively included. The purpose of this study was to examine robustness and dose variation due to setup uncertainty and anatomical change in IMPT of lung cancer.
  
  
  METHODS
  Plans were generated with multi-field optimization based on planning target volume (MFO-PTV) and worst-case robust optimization (MFO-RO) on simulation computed tomography scans (CT0) for nine patients. Robustness was evaluated on the CT0 by computing the standard deviation of DVH (SD-DVH). Dose variations calculated on weekly CTs were compared with SD-DVH. Equivalent uniform dose (EUD) change from the original plan on weekly dose was also calculated for both plans.
  
  
  RESULTS
  SD-DVH and dose variation on weekly CTs were both significantly lower in the MFO-RO plans than in the MFO-PTV plans for targets, lungs, and the esophagus (p<0.05). When comparing EUD for ITV between weekly and planned dose distributions, three patients and 28% of repeated CTs for MFO-RO plans, and six patients and 44% of repeated CTs for MFO-PTV plans, respectively, showed an EUD change of >5%.
  
  
  CONCLUSIONS
  RO in IMPT reduces the dose variation due to setup uncertainty and anatomy changes during treatment compared with PTV-based planning. However, dose variation could still be substantial; repeated imaging and adaptive planning as needed are highly recommended for IMPT of lung tumors.
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA. Electronic address: hengli@mdanderson.org.
authors.forename: Heng
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, Scottsdale, AZ, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Joe
authors.initials: J
authors.lastname: Chang
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Frank
authors.affiliation: Applied Research, Varian Medical Systems, Palo Alto, CA, USA.
authors.forename: Yupeng
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Falk
authors.initials: F
authors.lastname: Poenisch
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Gillin
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Ronald
authors.initials: R
authors.lastname: Zhu
mesh_terms: D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014057:Tomography, X-Ray Computed; D035501:Uncertainty
keywords: Adaptive planning; IMPT; Robust optimization; Robustness evaluation