title: Intensity modulated arc therapy implementation in a three phase adaptive (18)F-FDG-PET voxel intensity-based planning strategy for head-and-neck cancer.
abstract: BACKGROUND
  This study investigates the implementation of a new intensity modulated arc therapy (IMAT) class solution in comparison to a 6-static beam step-and-shoot intensity modulated radiotherapy (s-IMRT) for three-phase adaptive (18)F-FDG-PET-voxel-based dose-painting-by-numbers (DPBN) for head-and-neck cancer.
  
  
  METHODS
  We developed (18)F-FDG-PET-voxel intensity-based IMAT employing multiple arcs and compared it to clinically used s-IMRT DPBN. Three IMAT plans using (18)F-FDG-PET/CT acquired before treatment (phase I), after 8 fractions (phase II) and CT acquired after 18 fractions (phase III) were generated for each of 10 patients treated with 3 s-IMRT plans based on the same image sets. Based on deformable image registration (ABAS, version 0.41, Elekta CMS Software, Maryland Heights, MO), doses of the 3 plans were summed on the pretreatment CT using validated in-house developed software. Dosimetric indices in targets and organs-at-risk (OARs), biologic conformity of treatment plans set at ≤5 %, treatment quality and efficiency were compared between IMAT and s-IMRT for the whole group and for individual patients.
  
  
  RESULTS
  Doses to most organs-at-risk (OARs) were significantly better in IMAT plans, while target levels were similar for both types of plans. On average, IMAT ipsilateral and contralateral parotid mean doses were 14.0 % (p = 0.001) and 12.7 % (p < 0.001) lower, respectively. Pharyngeal constrictors D50% levels were similar or reduced with up to 54.9 % for IMAT compared to s-IMRT for individual patient cases. IMAT significantly improved biologic conformity by 2.1 % for treatment phases I and II. 3D phantom measurements reported an agreement of ≥95 % for 3 % and 3 mm criteria for both treatment modalities. IMAT delivery time was significantly shortened on average by 41.1 %.
  
  
  CONCLUSIONS
  IMAT implementation significantly improved the biologic conformity as compared to s-IMRT in adaptive dose-escalated DPBN treatments. The better OAR sparing and faster delivery highly improved the treatment efficiency.
authors.affiliation: Department of Radiotherapy, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium. dieter.berwouts@ugent.be.|Department of Nuclear Medicine, Ghent University Hospital, Ghent, Belgium. dieter.berwouts@ugent.be.
authors.forename: Dieter
authors.initials: D
authors.lastname: Berwouts
authors.affiliation: Department of Radiotherapy, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Luiza Ana Maria
authors.initials: LA
authors.lastname: Olteanu
authors.affiliation: Ghent University, Ghent, Belgium.
authors.forename: Bruno
authors.initials: B
authors.lastname: Speleers
authors.affiliation: Department of Radiotherapy, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Duprez
authors.affiliation: Ghent University, Ghent, Belgium.|Zürich University Hospital, Zürich, Switzerland.
authors.forename: Indira
authors.initials: I
authors.lastname: Madani
authors.affiliation: Department of Radiotherapy, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Tom
authors.initials: T
authors.lastname: Vercauteren
authors.affiliation: Department of Radiotherapy, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.|Ghent University, Ghent, Belgium.
authors.forename: Wilfried
authors.initials: W
authors.lastname: De Neve
authors.affiliation: Ghent University, Ghent, Belgium.
authors.forename: Werner
authors.initials: W
authors.lastname: De Gersem
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D019788:Fluorodeoxyglucose F18; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008875:Middle Aged; D058958:Organs at Risk; D000072078:Positron Emission Tomography Computed Tomography; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: Adaptive intensity modulated arc therapy; Dose-painting; Head-and-neck cancer; Intensity modulated radiotherapy