title: Relative plan robustness of step-and-shoot vs rotational intensity-modulated radiotherapy on repeat computed tomographic simulation for weight loss in head and neck cancer.
abstract: BACKGROUND
  Interfractional anatomical alterations may have a differential effect on the dose delivered by step-and-shoot intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). The increased degrees of freedom afforded by rotational delivery may increase plan robustness (measured by change in target volume coverage and doses to organs at risk [OARs]). However, this has not been evaluated for head and neck cancer.
  
  
  METHODS
  A total of 10 patients who required repeat computed tomography (CT) simulation and replanning during head and neck IMRT were included. Step-and-shoot IMRT and VMAT plans were generated from the original planning scan. The initial and second CT simulation scans were fused and targets/OAR contours transferred, reviewed, and modified. The plans were applied to the second CT scan and doses recalculated without repeat optimization. Differences between step-and-shoot IMRT and VMAT for change in target volume coverage and doses to OARs between first and second CT scans were compared by Wilcoxon signed rank test.
  
  
  RESULTS
  There were clinically relevant dosimetric changes between the first and the second CT scans for both the techniques (reduction in mean D95% for PTV2 and PTV3, Dmin for CTV2 and CTV3, and increased mean doses to the parotid glands). However, there were no significant differences between step-and-shoot IMRT and VMAT for change in any target coverage parameter (including D95% for PTV2 and PTV3 and Dmin for CTV2 and CTV3) or dose to any OARs (including parotid glands) between the first and the second CT scans.
  
  
  CONCLUSIONS
  For patients with head and neck cancer who required replanning mainly due to weight loss, there were no significant differences in plan robustness between step-and-shoot IMRT and VMAT. This information is useful with increased clinical adoption of VMAT.
authors.affiliation: Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK; The University of Manchester, Manchester Academic Health Science Centre, Institute of Cancer Sciences, Manchester, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Thomson
authors.affiliation: The University of Manchester, Manchester Academic Health Science Centre, Institute of Cancer Sciences, Manchester, UK; Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK.
authors.forename: William J
authors.initials: WJ
authors.lastname: Beasley
authors.affiliation: Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK.
authors.forename: Kate
authors.initials: K
authors.lastname: Garcez
authors.affiliation: Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK.
authors.forename: Lip W
authors.initials: LW
authors.lastname: Lee
authors.affiliation: Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Sykes
authors.affiliation: The University of Manchester, Manchester Academic Health Science Centre, Institute of Cancer Sciences, Manchester, UK; Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK.
authors.forename: Carl G
authors.initials: CG
authors.lastname: Rowbottom
authors.affiliation: Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK; The University of Manchester, Manchester Academic Health Science Centre, Institute of Cancer Sciences, Manchester, UK. Electronic address: nick.slevin@christie.nhs.uk.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Slevin
mesh_terms: D000368:Aged; D005260:Female; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden; D015431:Weight Loss
keywords: Adaptive; IMRT; Replanning; Robustness; VMAT