title: Do we need daily image-guided radiotherapy by megavoltage computed tomography in head and neck helical tomotherapy? The actual delivered dose to the spinal cord.
abstract: OBJECTIVE
  To quantify the actual delivered dose to the cervical spinal cord with different image-guided radiotherapy (IGRT) approaches during head and neck (HN) cancer helical tomotherapy.
  
  
  METHODS
  Twenty HN patients (HNpts) treated with bilateral nodal irradiation were analyzed. Daily megavoltage computed tomography MVCT) scans were performed for setup purposes. The maximum dose on the planning CT scan (plan-Dmax) and the magnitude and localization of the actual delivered Dmax (a-Dmax) were analyzed for four scenarios: daily image-guided radiotherapy (dIGRT), twice weekly IGRT (2×WkIGRT), once weekly IGRT (1×WkIGRT), and no IGRT at all (non-IGRT). The spinal cord was recontoured on 236 MVCTs for each scenario (total, 944 fractions), and the delivered dose was recalculated for each fraction (fx) separately.
  
  
  RESULTS
  Fifty-one percent of the analyzed fx for dIGRT, 56% of the analyzed fx for the 2×WkIGRT, 62% of the analyzed fx for the 1×WkIGRT, and 63% of the analyzed fx for the non-IGRT scenarios received a higher a-Dmax than the plan-Dmax. The median increase of dose in these fx was 3.3% more for dIGRT, 5.8% more for 2×WkIGRT, 10.0% more for 1×WkIGRT, and 9.5% more for non-IGRT than the plan-Dmax. The median spinal cord volumes receiving a higher dose than the plan-Dmax were 0.02 cm³ for dIGRT, 0.11 cm³ for 2×WkIGRT, 0.31 cm³ for 1×WkIGRT, and 0.22 cm³ for non-IGRT. Differences between the dIGRT and all other scenarios were statistically significant (p < 0.05).
  
  
  CONCLUSIONS
  Compared to the Dmax of the initial plan, daily IGRT had the smallest increase in dose. Furthermore, daily IGRT had the lowest proportion of fractions and the smallest volumes affected by a dose that was higher than the planned dose. For patients treated with doses close to the tolerance dose of the spinal cord, we recommend daily IGRT. For all other cases, twice weekly IGRT is sufficient.
authors.affiliation: Department of Radiation Oncology, Technische Universität München, Klinikum rechts der Isar, München, Germany. Marciana.Duma@lrz.tumuenchen.de
authors.forename: Marciana Nona
authors.initials: MN
authors.lastname: Duma
authors.forename: Severin
authors.initials: S
authors.lastname: Kampfer
authors.forename: Tibor
authors.initials: T
authors.lastname: Schuster
authors.forename: Nandana
authors.initials: N
authors.lastname: Aswathanarayana
authors.forename: Laura-Sophie
authors.initials: LS
authors.lastname: Fromm
authors.forename: Michael
authors.initials: M
authors.lastname: Molls
authors.forename: Nicolaus
authors.initials: N
authors.lastname: Andratschke
authors.forename: Hans
authors.initials: H
authors.lastname: Geinitz
mesh_terms: D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D015182:Lymphatic Irradiation / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D009333:Neck; D011880:Radiotherapy Planning, Computer-Assisted; D061106:Radiotherapy Setup Errors; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000528:radiation effects*; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014067:Tonsillar Neoplasms / Q000532:radiotherapy*; D035501:Uncertainty