title: Dose-volume and biological-model based comparison between helical tomotherapy and (inverse-planned) IMAT for prostate tumours.
abstract: OBJECTIVE
  Helical tomotherapy (HT) and intensity-modulated arc therapy (IMAT) are two arc-based approaches to the delivery of intensity-modulated radiotherapy (IMRT). Through plan comparisons we have investigated the potential of IMAT, both with constant (conventional or IMAT-C) and variable (non-conventional or IMAT-NC, a theoretical exercise) dose-rate, to serve as an alternative to helical tomotherapy.
  
  
  METHODS
  Six patients with prostate tumours treated by HT with a moderately hypo-fractionated protocol, involving a simultaneous integrated boost, were re-planned as IMAT treatments. A method for IMAT inverse-planning using a commercial module for static IMRT combined with a multi-leaf collimator (MLC) arc-sequencing was developed. IMAT plans were compared to HT plans in terms of dose statistics and radiobiological indices.
  
  
  RESULTS
  Concerning the planning target volume (PTV), the mean doses for all PTVs were similar for HT and IMAT-C plans with minimum dose, target coverage, equivalent uniform dose (EUD) and tumour control probability (TCP) values being generally higher for HT; maximum dose and degree of heterogeneity were instead higher for IMAT-C. In relation to organs at risk, mean doses and normal tissue complication probability (NTCP) values were similar between the two modalities, except for the penile bulb where IMAT was significantly better. Re-normalizing all plans to the same rectal toxicity (NTCP=5%), the HT modality yielded higher TCP than IMAT-C but there was no significant difference between HT and IMAT-NC. The integral dose with HT was higher than that for IMAT.
  
  
  CONCLUSIONS
  with regards to the plan analysis, the HT is superior to IMAT-C in terms of target coverage and dose homogeneity within the PTV. Introducing dose-rate variation during arc-rotation, not deliverable with current linac technology, the simulations result in comparable plan indices between (IMAT-NC) and HT.
authors.affiliation: Department of Medical Physics, S. Maria Nuova Hospital, Reggio Emilia, Italy. iori.mauro@asmn.re.it
authors.forename: Mauro
authors.initials: M
authors.lastname: Iori
authors.forename: Giovanni Mauro
authors.initials: GM
authors.lastname: Cattaneo
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Cagni
authors.forename: Claudio
authors.initials: C
authors.lastname: Fiorino
authors.forename: Gianni
authors.initials: G
authors.lastname: Borasi
authors.forename: Calandrino
authors.initials: C
authors.lastname: Riccardo
authors.forename: Cinzia
authors.initials: C
authors.lastname: Iotti
authors.forename: Ferruccio
authors.initials: F
authors.lastname: Fazio
authors.forename: Alan E
authors.initials: AE
authors.lastname: Nahum
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D015641:Radiography, Interventional / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D018709:Statistics, Nonparametric; D036542:Tomography, Spiral Computed