title: Evaluation and mitigation of the interplay effects of intensity modulated proton therapy for lung cancer in a clinical setting.
abstract: OBJECTIVE
  The primary aim of this study was to evaluate the impact of the interplay effects of intensity modulated proton therapy (IMPT) plans for lung cancer in the clinical setting. The secondary aim was to explore the technique of isolayered rescanning to mitigate these interplay effects.
  
  
  METHODS
  A single-fraction 4-dimensional (4D) dynamic dose without considering rescanning (1FX dynamic dose) was used as a metric to determine the magnitude of dosimetric degradation caused by 4D interplay effects. The 1FX dynamic dose was calculated by simulating the machine delivery processes of proton spot scanning on a moving patient, described by 4D computed tomography during IMPT delivery. The dose contributed from an individual spot was fully calculated on the respiratory phase that corresponded to the life span of that spot, and the final dose was accumulated to a reference computed tomography phase by use of deformable image registration. The 1FX dynamic dose was compared with the 4D composite dose. Seven patients with various tumor volumes and motions were selected for study.
  
  
  RESULTS
  The clinical target volume (CTV) prescription coverage for the 7 patients was 95.04%, 95.38%, 95.39%, 95.24%, 95.65%, 95.90%, and 95.53% when calculated with the 4D composite dose and 89.30%, 94.70%, 85.47%, 94.09%, 79.69%, 91.20%, and 94.19% when calculated with the 1FX dynamic dose. For these 7 patients, the CTV coverage calculated by use of a single-fraction dynamic dose was 95.52%, 95.32%, 96.36%, 95.28%, 94.32%, 95.53%, and 95.78%, with a maximum monitor unit limit value of 0.005. In other words, by increasing the number of delivered spots in each fraction, the degradation of CTV coverage improved up to 14.6%.
  
  
  CONCLUSIONS
  A single-fraction 4D dynamic dose without rescanning was validated as a surrogate to evaluate the interplay effects of IMPT for lung cancer in the clinical setting. The interplay effects potentially can be mitigated by increasing the amount of isolayered rescanning in each fraction delivery.
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; Department of Industrial Engineering, The University of Houston, Houston, Texas.
authors.forename: Laleh
authors.initials: L
authors.lastname: Kardar
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; Applied Research, Varian Medical Systems, 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: Xiaoqiang
authors.initials: X
authors.lastname: Li
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; Department of Industrial Engineering, The University of Houston, Houston, Texas.
authors.forename: Wenhua
authors.initials: W
authors.lastname: Cao
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Joe Y
authors.initials: JY
authors.lastname: Chang
authors.affiliation: Department of Industrial Engineering, The University of Houston, Houston, Texas.
authors.forename: Li
authors.initials: L
authors.lastname: Liao
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Ronald X
authors.initials: RX
authors.lastname: Zhu
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: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Michael
authors.initials: M
authors.lastname: Gillin
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: James D
authors.initials: JD
authors.lastname: Cox
authors.affiliation: Department of Industrial Engineering, The University of Houston, Houston, Texas.
authors.forename: Gino
authors.initials: G
authors.lastname: Lim
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas. Electronic address: xizhang@mdanderson.org.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhang
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000503:physiopathology / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000503:physiopathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D015656:Respiratory Mechanics; D011522:Protons
chemical_list: D011522:Protons