title: Rotational IMRT techniques compared to fixed gantry IMRT and tomotherapy: multi-institutional planning study for head-and-neck cases.
abstract: BACKGROUND
  Recent developments enable to deliver rotational IMRT with standard C-arm gantry based linear accelerators. This upcoming treatment technique was benchmarked in a multi-center treatment planning study against static gantry IMRT and rotational IMRT based on a ring gantry for a complex parotid gland sparing head-and-neck technique.
  
  
  METHODS
  Treatment plans were created for 10 patients with head-and-neck tumours (oropharynx, hypopharynx, larynx) using the following treatment planning systems (TPS) for rotational IMRT: Monaco (ELEKTA VMAT solution), Eclipse (Varian RapidArc solution) and HiArt for the helical tomotherapy (Tomotherapy). Planning of static gantry IMRT was performed with KonRad, Pinnacle and Panther DAO based on step&shoot IMRT delivery and Eclipse for sliding window IMRT. The prescribed doses for the high dose PTVs were 65.1Gy or 60.9Gy and for the low dose PTVs 55.8Gy or 52.5Gy dependend on resection status. Plan evaluation was based on target coverage, conformity and homogeneity, DVHs of OARs and the volume of normal tissue receiving more than 5Gy (V5Gy). Additionally, the cumulative monitor units (MUs) and treatment times of the different technologies were compared. All evaluation parameters were averaged over all 10 patients for each technique and planning modality.
  
  
  RESULTS
  Depending on IMRT technique and TPS, the mean CI values of all patients ranged from 1.17 to 2.82; and mean HI values varied from 0.05 to 0.10. The mean values of the median doses of the spared parotid were 26.5Gy for RapidArc and 23Gy for VMAT, 14.1Gy for Tomo. For fixed gantry techniques 21Gy was achieved for step&shoot+KonRad, 17.0Gy for step&shoot+Panther DAO, 23.3Gy for step&shoot+Pinnacle and 18.6Gy for sliding window.V5Gy values were lowest for the sliding window IMRT technique (3499 ccm) and largest for RapidArc (5480 ccm). The lowest mean MU value of 408 was achieved by Panther DAO, compared to 1140 for sliding window IMRT.
  
  
  CONCLUSIONS
  All IMRT delivery technologies with their associated TPS provide plans with satisfying target coverage while at the same time respecting the defined OAR criteria. Sliding window IMRT, RapidArc and Tomo techniques resulted in better target dose homogeneity compared to VMAT and step&shoot IMRT. Rotational IMRT based on C-arm linacs and Tomotherapy seem to be advantageous with respect to OAR sparing and treatment delivery efficiency, at the cost of higher dose delivered to normal tissues. The overall treatment plan quality using Tomo seems to be better than the other TPS technology combinations.
authors.affiliation: Department of Radiation Oncology, University of Jena, Jena, Germany. tilo.wiezorek@med.uni-jena.de
authors.forename: Tilo
authors.initials: T
authors.lastname: Wiezorek
authors.forename: Tim
authors.initials: T
authors.lastname: Brachwitz
authors.forename: Dietmar
authors.initials: D
authors.lastname: Georg
authors.forename: Eyck
authors.initials: E
authors.lastname: Blank
authors.forename: Irina
authors.initials: I
authors.lastname: Fotina
authors.forename: Gregor
authors.initials: G
authors.lastname: Habl
authors.forename: Matthias
authors.initials: M
authors.lastname: Kretschmer
authors.forename: Gerd
authors.initials: G
authors.lastname: Lutters
authors.forename: Henning
authors.initials: H
authors.lastname: Salz
authors.forename: Kai
authors.initials: K
authors.lastname: Schubert
authors.forename: Daniela
authors.initials: D
authors.lastname: Wagner
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Wendt
mesh_terms: D000465:Algorithms; D002277:Carcinoma / Q000532:radiotherapy*; D004867:Equipment Design; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D058958:Organs at Risk / Q000528:radiation effects; D010315:Particle Accelerators / Q000295:instrumentation; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D012399:Rotation