title: Patient-specific quantification of respiratory motion-induced dose uncertainty for step-and-shoot IMRT of lung cancer.
abstract: OBJECTIVE
  The objective of this study was to quantify respiratory motion-induced dose uncertainty at the planning stage for step-and-shoot intensity-modulated radiation therapy (IMRT) using an analytical technique.
  
  
  METHODS
  Ten patients with stage II∕III lung cancer who had undergone a planning four-dimensional (4D) computed tomographic scan and step-and-shoot IMRT planning were selected with a mix of motion and tumor size for this retrospective study. A step-and-shoot IMRT plan was generated for each patient. The maximum and minimum doses with respiratory motion were calculated for each plan, and the mean deviation from the 4D dose was calculated, taking delivery time, fractionation, and patient breathing cycle into consideration.
  
  
  RESULTS
  For all patients evaluated in this study, the mean deviation from the 4D dose in the planning target volume (PTV) was <2.5%, with a standard deviation <1.2%, and maximum point dose variation from the 4D dose was <6.2% in the PTV assuming delivery dose rate of 200 MU∕min and patient breathing cycle of 8 s. The motion-induced dose uncertainty is a function of motion, fractionation, MU (plan modulation), dose rate, and patient breathing cycle.
  
  
  CONCLUSIONS
  Respiratory motion-induced dose uncertainty varies from patient to patient. Therefore, it is important to evaluate the dose uncertainty on a patient-specific basis, which could be useful for plan evaluation and treatment strategy determination for selected patients.
authors: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors: Heng
authors: H
authors: Li
authors: Peter
authors: P
authors: Park
authors: Wei
authors: W
authors: Liu
authors: Jason
authors: J
authors: Matney
authors: Zhongxing
authors: Z
authors: Liao
authors: Peter
authors: P
authors: Balter
authors: Yupeng
authors: Y
authors: Li
authors: Xiaodong
authors: X
authors: Zhang
authors: Xiaoqiang
authors: X
authors: Li
authors: X Ronald
authors: XR
authors: Zhu
mesh_terms: D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology / Q000532:radiotherapy*; D009068:Movement; D057285:Precision Medicine; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies; D047368:Tumor Burden; D035501:Uncertainty