title: Assessment of interfraction patient setup for head-and-neck cancer intensity modulated radiation therapy using multiple computed tomography-based image guidance.
abstract: OBJECTIVE
  Various image guidance systems are commonly used in conjunction with intensity modulated radiation therapy (IMRT) in head-and-neck cancer irradiation. The purpose of this study was to assess interfraction patient setup variations for 3 computed tomography (CT)-based on-board image guided radiation therapy (IGRT) modalities.
  
  
  METHODS
  A total of 3302 CT scans for 117 patients, including 53 patients receiving megavoltage cone-beam CT (MVCBCT), 29 receiving kilovoltage cone-beam CT (KVCBCT), and 35 receiving megavoltage fan-beam CT (MVFBCT), were retrospectively analyzed. The daily variations in the mediolateral (ML), craniocaudal (CC), and anteroposterior (AP) dimensions were measured. The clinical target volume-to-planned target volume (CTV-to-PTV) margins were calculated using 2.5Σ + 0.7 σ, where Σ and σ were systematic and random positioning errors, respectively. Various patient characteristics for the MVCBCT group, including weight, weight loss, tumor location, and initial body mass index, were analyzed to determine their possible correlation with daily patient setup.
  
  
  RESULTS
  The average interfraction displacements (± standard deviation) in the ML, CC, and AP directions were 0.5 ± 1.5, -0.3 ± 2.0, and 0.3 ± 1.7 mm (KVCBCT); 0.2 ± 1.9, -0.2 ± 2.4, and 0.0 ± 1.7 mm (MVFBCT); and 0.0 ± 1.8, 0.5 ± 1.7, and 0.8 ± 3.0 mm (MVCBCT). The day-to-day random errors for KVCBCT, MVFBCT, and MVCBCT were 1.4-1.6, 1.7, and 2.0-2.1 mm. The interobserver variations were 0.8, 1.1, and 0.7 mm (MVCBCT); 0.5, 0.4, and 0.8 mm (MVFBCT); and 0.5, 0.4, and 0.6 mm (KVCBCT) in the ML, CC, and AP directions, respectively. The maximal calculated uniform CTV-to-PTV margins were 5.6, 6.9, and 8.9 mm for KVCBCT, MVFBCT, and MVCBCT, respectively. For the evaluated patient characteristics, the calculated margins for different patient parameters appeared to differ; analysis of variance (ANOVA) and/or t test analysis found no statistically significant setup difference in any direction.
  
  
  CONCLUSIONS
  Daily random setup errors and CTV-to-PTV margins for treatment of head-and-neck cancer were affected by imaging quality. Our data indicated that larger margins were associated with MVFBCT and MVCBCT, compared with smaller margins for KVCBCT. IGRT modalities with better image quality are encouraged in clinical practice.
authors.affiliation: Department of Radiation Oncology, David of Geffen School of Medicine at UCLA, Los Angeles, California, USA. xqi@mednet.ucla.edu
authors.forename: X Sharon
authors.initials: XS
authors.lastname: Qi
authors.forename: Angie Y
authors.initials: AY
authors.lastname: Hu
authors.forename: Steve P
authors.initials: SP
authors.lastname: Lee
authors.forename: Percy
authors.initials: P
authors.lastname: Lee
authors.forename: John
authors.initials: J
authors.lastname: DeMarco
authors.forename: X Allen
authors.initials: XA
authors.lastname: Li
authors.forename: Michael L
authors.initials: ML
authors.lastname: Steinberg
authors.forename: Patrick
authors.initials: P
authors.lastname: Kupelian
authors.forename: Daniel
authors.initials: D
authors.lastname: Low
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005260:Female; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D061106:Radiotherapy Setup Errors / Q000517:prevention & control; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D047368:Tumor Burden; D055815:Young Adult