title: A criterion for the reliable use of MRI-only radiotherapy.
abstract: BACKGROUND
  MRI-only radiotherapy will eliminate the systematic registration errors introduced when transferring MRI information to the CT. However, challenges concerning the missing information on electron density, necessary for dose calculation and patient setup on bony anatomy are introduced. This study presents a possible statistical approach to evaluate, if deviations based on MRI-only radiotherapy as compared to the CT based radiotherapy are acceptable.
  
  
  METHODS
  18 head-and-neck, 21 prostate, 10 vesica and 8 pelvic patients were included in the study. Data from each patient contained a CT and a T2-weighted MRI scan, a structure set and a clinically approved CT based treatment plan, which was re-calculated with identical parameters on the density corrected MRI scans. A statistical analysis including a 95% confidence interval was performed in clinically relevant DVH points.
  
  
  RESULTS
  The mean differences in the investigated DVH points were in the order of 1.5% for the PTV and up to 4.2% for organs at risk. In addition, a proposed criterion of 2% dose difference in the PTV coverage for 95% of the patients was fulfilled for all diagnostic groups for a bulk segmented MRI in the DVH points, D(median) and D2%, while only head-and-neck and prostate further fulfilled the criterion in D98%.
  
  
  CONCLUSIONS
  Here, we suggested a method for establishing a reliable use of MRI-only radiotherapy. A population-based study comparing CT based dose calculations with those obtained on a suggested segmentation of MRI should be initiated and acceptable deviations in clinically relevant DVH points should be established. Such a population-based approach could form a part of the clinical commissioning of MRI-only radiotherapy.
authors.affiliation: Department of Oncology, Radiotherapy Research Unit (52AA), Herlev Hospital, University of Copenhagen, Herlev, Denmark. marie.elgaard@gmail.com.
authors.forename: Marie E
authors.initials: ME
authors.lastname: Korsholm
authors.forename: Line W
authors.initials: LW
authors.lastname: Waring
authors.forename: Jens M
authors.initials: JM
authors.lastname: Edmund
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006258:Head and Neck Neoplasms / Q000175:diagnosis / Q000453:epidemiology / Q000532:radiotherapy; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D010386:Pelvic Neoplasms / Q000175:diagnosis / Q000453:epidemiology / Q000532:radiotherapy; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000453:epidemiology / Q000532:radiotherapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D061089:Radiotherapy, Image-Guided / Q000379:methods* / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D001749:Urinary Bladder Neoplasms / Q000175:diagnosis / Q000453:epidemiology / Q000532:radiotherapy