title: Dosimetric comparison between helical tomotherapy and volumetric modulated arc-therapy for non-anaplastic thyroid cancer treatment.
abstract: BACKGROUND
  To evaluate and compare dosimetric parameters of volumetric modulated arctherapy (VMAT) and helical tomotherapy (HT) for non-anaplastic thyroid cancer adjuvant radiotherapy.
  
  
  METHODS
  Twelve patients with non-anaplastic thyroid cancer at high risk of local relapse received adjuvant external beam radiotherapy with curative intent in our institution, using a two-dose level prescription with a simultaneous integrated boost approach. Each patient was re-planned by the same physicist twice using both VMAT and HT. Several dosimetric quality indexes were used: target coverage index (proportion of the target volume covered by the reference isodose), healthy tissue conformity index (proportion of the reference isodose volume including the target volume), conformation number (combining both previous indexes), Dice Similarity Coefficient (DSC), and homogeneity index ((D2%-D98%)/prescribed dose). Dose-volume histogram statistics were also compared.
  
  
  RESULTS
  HT provided statistically better target coverage index and homogeneity index for low risk PTV in comparison with VMAT (respectively 0.99 vs. 0.97 (p=0.008) and 0.22 vs. 0.25 (p=0.016)). However, HT provided poorer results for healthy tissue conformity index, conformation number and DSC with low risk and high risk PTV. As regards organs at risk sparing, by comparison with VMAT, HT statistically decreased the D2% to medullary canal (25.3 Gy vs. 32.6 Gy (p=0.003)). Besides, HT allowed a slight sparing dose for the controlateral parotid (Dmean: 4.3 Gy vs. 6.6 Gy (p=0.032)) and for the controlateral sub-maxillary gland (Dmean: 29.1 Gy vs. 33.1 Gy (p=0.041)).
  
  
  CONCLUSIONS
  Both VMAT and HT techniques for adjuvant treatment of non-anaplastic thyroid cancer provide globally attractive treatment plans with slight dosimetric differences. However, helical tomotherapy clearly provides a benefit in term of medullary canal sparing.
authors.affiliation: Department of Radiation Oncology, Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse, Oncopôle - 1, avenue Irène Joliot Curie, 31059, Toulouse, France. jonathan.khalifa@hotmail.fr.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Khalifa
authors.affiliation: Department of Medical Physics, Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse, Oncopôle - 1, avenue Irène Joliot Curie, 31059, Toulouse, France. vieillevigne.laure@iuct-oncopole.fr.
authors.forename: Laure
authors.initials: L
authors.lastname: Vieillevigne
authors.affiliation: Department of Radiation Oncology, Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse, Oncopôle - 1, avenue Irène Joliot Curie, 31059, Toulouse, France. boyrie.sabrina@iuct-oncopole.fr.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Boyrie
authors.affiliation: Department of Biostatistics, Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse, Oncopôle - 1, avenue Irène Joliot Curie, 31059, Toulouse, France. ouali.monia@iuct-oncopole.fr.
authors.forename: Monia
authors.initials: M
authors.lastname: Ouali
authors.affiliation: Department of Biostatistics, Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse, Oncopôle - 1, avenue Irène Joliot Curie, 31059, Toulouse, France. filleron.thomas@iuct-oncopole.fr.
authors.forename: Thomas
authors.initials: T
authors.lastname: Filleron
authors.affiliation: Department of Radiation Oncology, Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse, Oncopôle - 1, avenue Irène Joliot Curie, 31059, Toulouse, France. rives.michel@iuct-oncopole.fr.
authors.forename: Michel
authors.initials: M
authors.lastname: Rives
authors.affiliation: Department of Radiation Oncology, Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse, Oncopôle - 1, avenue Irène Joliot Curie, 31059, Toulouse, France. laprie.anne@iuct-oncopole.fr.|Université Toulouse III Paul Sabatier, Toulouse, F-31000, France. laprie.anne@iuct-oncopole.fr.|INSERM, UMR825, Toulouse, 24 F-31059, France. laprie.anne@iuct-oncopole.fr.
authors.forename: Anne
authors.initials: A
authors.lastname: Laprie
mesh_terms: D006801:Humans; D058958:Organs at Risk; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013964:Thyroid Neoplasms / Q000532:radiotherapy*