title: Magnetic resonance-only simulation and dose calculation in external beam radiation therapy: a feasibility study for pelvic cancers.
abstract: BACKGROUND
  The clinical feasibility of using pseudo-computed tomography (pCT) images derived from magnetic resonance (MR) images for external bean radiation therapy (EBRT) planning for prostate cancer patients has been well demonstrated. This paper investigates the feasibility of applying an MR-derived, pCT planning approach to additional types of cancer in the pelvis.
  
  
  METHODS
  Fifteen patients (five prostate cancer patients, five rectal cancer patients, and five gynecological cancer patients) receiving EBRT at Turku University Hospital (Turku, Finland) were included in the study. Images from an MRCAT (Magnetic Resonance for Calculating ATtenuation, Philips, Vantaa, Finland) pCT method were generated as a part of a clinical MR-simulation procedure. Dose calculation accuracy was assessed by comparing the pCT-based calculation with a CT-based calculation. In addition, the degree of geometric accuracy was studied.
  
  
  RESULTS
  The median relative difference of PTV mean dose between CT and pCT images was within 0.8% for all tumor types. When assessing the tumor site-specific accuracy, the median [range] relative dose differences to the PTV mean were 0.7 [-0.11;1.05]% for the prostate cases, 0.3 [-0.25;0.57]% for the rectal cases, and 0.09 [-0.69;0.25]% for the gynecological cancer cases. System-induced geometric distortion was measured to be less than 1 mm for all PTV volumes and the effect on the PTV median dose was less than 0.1%.
  
  
  CONCLUSIONS
  According to the comparison, using pCT for clinical EBRT planning and dose calculation in the three investigated types of pelvic cancers is feasible. Further studies are required to demonstrate the applicability to a larger cohort of patients.
authors.affiliation: a Philips MR Therapy , Vantaa , Finland.|b Department of Neuroscience and Biomedical Engineering , Aalto University School of Science , Espoo , Finland.
authors.forename: Reko
authors.initials: R
authors.lastname: Kemppainen
authors.affiliation: c Department of Medical Physics , Turku University Hospital , Turku , Finland.|d Department of Oncology and Radiotherapy , Turku University Hospital , Turku , Finland.
authors.forename: Sami
authors.initials: S
authors.lastname: Suilamo
authors.affiliation: e Turku PET-Centre, Turku University Hospital, Finland and University of Turku , Turku , Finland.
authors.forename: Terhi
authors.initials: T
authors.lastname: Tuokkola
authors.affiliation: d Department of Oncology and Radiotherapy , Turku University Hospital , Turku , Finland.
authors.forename: Paula
authors.initials: P
authors.lastname: Lindholm
authors.affiliation: a Philips MR Therapy , Vantaa , Finland.
authors.forename: Martin H
authors.initials: MH
authors.lastname: Deppe
authors.affiliation: c Department of Medical Physics , Turku University Hospital , Turku , Finland.|d Department of Oncology and Radiotherapy , Turku University Hospital , Turku , Finland.
authors.forename: Jani
authors.initials: J
authors.lastname: Keyriläinen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005240:Feasibility Studies; D005260:Female; D005833:Genital Neoplasms, Female / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D058958:Organs at Risk / Q000528:radiation effects; D010386:Pelvic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012004:Rectal Neoplasms / Q000473:pathology / Q000532:radiotherapy*