title: Helical tomotherapy versus single-arc intensity-modulated arc therapy: a collaborative dosimetric comparison between two institutions.
abstract: OBJECTIVE
  Both helical tomotherapy (HT) and single-arc intensity-modulated arc therapy (IMAT) deliver radiation using rotational beams with multileaf collimators. We report a dual-institution study comparing dosimetric aspects of these two modalities.
  
  
  METHODS
  Eight patients each were selected from the University of Maryland (UMM) and the University of Wisconsin Cancer Center Riverview (UWR), for a total of 16 cases. Four cancer sites including brain, head and neck (HN), lung, and prostate were selected. Single-arc IMAT plans were generated at UMM using Varian RapidArc (RA), and HT plans were generated at UWR using Hi-Art II TomoTherapy. All 16 cases were planned based on the identical anatomic contours, prescriptions, and planning objectives. All plans were swapped for analysis at the same time after final approval. Dose indices for targets and critical organs were compared based on dose-volume histograms, the beam-on time, monitor units, and estimated leakage dose. After the disclosure of comparison results, replanning was done for both techniques to minimize diversity in optimization focus from different operators.
  
  
  RESULTS
  For the 16 cases compared, the average beam-on time was 1.4 minutes for RA and 4.8 minutes for HT plans. HT provided better target dose homogeneity (7.6% for RA and 4.2% for HT) with a lower maximum dose (110% for RA and 105% for HT). Dose conformation numbers were comparable, with RA being superior to HT (0.67 vs. 0.60). The doses to normal tissues using these two techniques were comparable, with HT showing lower doses for more critical structures. After planning comparison results were exchanged, both techniques demonstrated improvements in dose distributions or treatment delivery times.
  
  
  CONCLUSIONS
  Both techniques created highly conformal plans that met or exceeded the planning goals. The delivery time and total monitor units were lower in RA than in HT plans, whereas HT provided higher target dose uniformity.
authors.affiliation: Department of Human Oncology and Medical Physics, University of Wisconsin-Madison, Madison, WI, USA. rong@humonc.wisc.edu
authors.forename: Yi
authors.initials: Y
authors.lastname: Rong
authors.forename: Grace
authors.initials: G
authors.lastname: Tang
authors.forename: James S
authors.initials: JS
authors.lastname: Welsh
authors.forename: Majid M
authors.initials: MM
authors.lastname: Mohiuddin
authors.forename: Bhudatt
authors.initials: B
authors.lastname: Paliwal
authors.forename: Cedric X
authors.initials: CX
authors.lastname: Yu
mesh_terms: D000465:Algorithms; D001932:Brain Neoplasms / Q000532:radiotherapy*; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007373:Interinstitutional Relations; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D008396:Maryland; D058958:Organs at Risk; D010315:Particle Accelerators; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014922:Wisconsin