title: A study on the dosimetric accuracy of treatment planning for stereotactic body radiation therapy of lung cancer using average and maximum intensity projection images.
abstract: OBJECTIVE
  To assess the accuracy of current stereotactic body radiation therapy (SBRT) lung treatment planning methodologies on irregular breathing patterns, we have performed a systematic dosimetric evaluation in phantoms by utilizing maximum intensity projection (MIP) and average (AVG) images generated from four dimensional computed tomography (4DCT).
  
  
  METHODS
  A custom built programmable lung phantom was used to simulate tumor motions due to various breathing patterns of patients. 4DCT scans were obtained in helical mode, and reconstructed AVG and MIP datasets were imported into the Pinnacle 8.0 h treatment planning system. SBRT plans were generated and executed, and delivered doses were measured by radiochromic film for analysis.
  
  
  RESULTS
  For targets moving regularly or irregularly within a small range (7.0+/-1.8 mm, n=6), we observed good agreement between the measured and computed dose distributions. However, for targets moving irregularly with a larger range (20.8+/-2.6 mm, n=4), the measured isodose lines were found to be shifted relative to the planned distribution, resulting in an under-dosing (over 10%) in a portion of the PTV. We further observed that the discrepancy between planned and measured dose distribution is due to the inaccurate representation of irregular target motion in the MIP images generated from 4DCT.
  
  
  CONCLUSIONS
  Caution should be used when planning from 4DCT images in the presence of large and irregular target motion. The inaccuracy inherent in 4DCT MIP and AVG images can be mitigated through the application of methodologies to reduce respiratory motion, such as abdominal compression, and through the use of volumetric image guidance (e.g., cone beam CT-CBCT) to assure precise targeting with minimal shifts.
authors.affiliation: Department Radiation Oncology, The University of Texas Southwestern Medical Center, Dallas, TX 75390-9183, USA.
authors.forename: Long
authors.initials: L
authors.lastname: Huang
authors.forename: Kwangyoul
authors.initials: K
authors.lastname: Park
authors.forename: Thomas
authors.initials: T
authors.lastname: Boike
authors.forename: Pam
authors.initials: P
authors.lastname: Lee
authors.forename: Lech
authors.initials: L
authors.lastname: Papiez
authors.forename: Timothy
authors.initials: T
authors.lastname: Solberg
authors.forename: Chuxiong
authors.initials: C
authors.lastname: Ding
authors.forename: Robert D
authors.initials: RD
authors.lastname: Timmerman
mesh_terms: D004307:Dose-Response Relationship, Radiation; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D008954:Models, Biological; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D055425:Respiratory-Gated Imaging Techniques; D012680:Sensitivity and Specificity