title: Effect of body mass index on shifts in ultrasound-based image-guided intensity-modulated radiation therapy for abdominal malignancies.
abstract: OBJECTIVE
  We investigated whether corrective shifts determined by daily ultrasound-based image-guidance correlate with body mass index (BMI) of patients treated with image-guided intensity-modulated radiation therapy (IG-IMRT) for abdominal malignancies. The utility of daily image-guidance, particularly for patients with BMI>25.0, is examined.
  
  
  METHODS
  Total 3162 ultrasound-directed shifts were performed in 86 patients. Direction and magnitude of shifts were correlated with pretreatment BMI. Bivariate statistical analysis and analysis of set-up correction data were performed using systematic and random error calculations.
  
  
  RESULTS
  Total 2040 daily alignments were performed. Average 3D vector of set-up correction for all patients was 12.1mm/fraction. Directional and absolute shifts and 3D vector length were significantly different between BMI cohorts. 3D displacement averaged 4.9 mm/fraction and 6.8mm/fraction for BMI < or = 25.0 and BMI>25.0, respectively. Systematic error in all axes and 3D vector was significantly greater for BMI>25.0. Differences in random error were not statistically significant.
  
  
  CONCLUSIONS
  Set-up corrections derived from daily ultrasound-based IG-IMRT of abdominal tumors correlated with BMI. Daily image-guidance may improve precision of IMRT delivery with benefits assessed for the entire population, particularly patients with increased habitus. Requisite PTV margins suggested in the absence of daily image-guidance are significantly greater in patients with BMI>25.0.
authors.affiliation: Department of Radiation Oncology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.
authors.forename: Mehee
authors.initials: M
authors.lastname: Choi
authors.forename: Clifton D
authors.initials: CD
authors.lastname: Fuller
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Wang
authors.forename: Ather
authors.initials: A
authors.lastname: Siddiqi
authors.forename: Adrian
authors.initials: A
authors.lastname: Wong
authors.forename: Charles R
authors.initials: CR
authors.lastname: Thomas
authors.forename: Martin
authors.initials: M
authors.lastname: Fuss
mesh_terms: D015992:Body Mass Index; D019583:Dose Fractionation, Radiation; D005260:Female; D005706:Gallbladder Neoplasms; D006801:Humans; D021621:Imaging, Three-Dimensional; D016018:Least-Squares Analysis; D008297:Male; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional