title: Carotid sparing hypofractionated tomotherapy in early glottic cancers: Refining image guided IMRT to improve morbidity.
abstract: OBJECTIVE
  Carotid artery damage has been reported secondary to radiotherapy. We report the feasibility of implementing hypofractionated laryngeal irradiation using carotid sparing tomotherapy (HT) and analyze the image guidance (IG) policy.
  
  
  METHODS
  Five patients with early glottic cancer (EGC) had radiotherapy using 3D conformal technique (conf) while repeat treatment plans were produced with helical tomotherapy using carotid sparing techniques (cstomo). Inverse and forward planned dose volume histograms were analyzed. Three hundred and sixty four daily images of 14 patients having daily Megavoltage head and neck CT imaging prior to irradiation were analyzed to assess errors.
  
  
  RESULTS
  There was no significant difference in the maximum and mean dose to the PTV (P = 0.058, 0.66). The left / right carotid median doses were significantly less in the cstomo plans as compared to conf plans (P = 0.0001/ 0.026). Cstomo plans had significantly better PTV Conformity Index (CI) (P = 0.0006) with comparable Homogeneity Index. A CTV-PTV margin of 5.3, 4, 5.3 cm in the 3 axes were calculated using Van Herks formula. After average shifts from imaging for first 5 fractions (AS5) were applied to remaining fractions, the residual shifts in the calculated CTV-PTV margins reduced to 2.9, and 2.1 in the X, Y axes respectively allowing further adaptation of PTV margin from fraction 6.
  
  
  CONCLUSIONS
  Carotid sparing was possible using cstomo plans with significantly better conformity. Applying AS5 could enable us to reduce the PTV (3 mm) margin in X, Y axes for the remaining 15 fractions.
authors.affiliation: Department of Radiotherapy, Tata Medical Center, Kolkata, India.
authors.forename: Sanjoy
authors.initials: S
authors.lastname: Chatterjee
authors.forename: Sourav
authors.initials: S
authors.lastname: Guha
authors.forename: Sriram
authors.initials: S
authors.lastname: Prasath
authors.forename: Indranil
authors.initials: I
authors.lastname: Mallick
authors.forename: Rimpa
authors.initials: R
authors.lastname: Achari
mesh_terms: D004947:Esophagus / Q000528:radiation effects; D005931:Glottis / Q000473:pathology*; D006801:Humans; D007822:Laryngeal Neoplasms / Q000150:complications / Q000532:radiotherapy*; D009017:Morbidity; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects; D013116:Spinal Cord / Q000528:radiation effects