title: MRI geometric distortion: Impact on tangential whole-breast IMRT.
abstract: The purpose of this study was to determine the impact of magnetic resonance imaging (MRI) geometric distortions when using MRI for target delineation and planning for whole-breast, intensity-modulated radiotherapy (IMRT). Residual system distortions and combined systematic and patient-induced distortions are considered. This retrospective study investigated 18 patients who underwent whole-breast external beam radiotherapy, where both CT and MRIs were acquired for treatment planning. Distortion phantoms were imaged on two MRI systems, dedicated to radiotherapy planning (a wide, closed-bore 3T and an open-bore 1T). Patient scans were acquired on the 3T system. To simulate MRI-based planning, distortion maps representing residual system distortions were generated via deformable registration between phantom CT and MRIs. Patient CT images and structures were altered to match the residual system distortion measured by the phantoms on each scanner. The patient CTs were also registered to the corresponding patient MRI scans, to assess patient and residual system effects. Tangential IMRT plans were generated and optimized on each resulting CT dataset, then propagated to the original patient CT space. The resulting dose distributions were then evaluated with respect to the standard clinically acceptable DVH and visual assessment criteria. Maximum residual systematic distortion was measured to be 7.9 mm (95%<4.7mm) and 11.9 mm (95%<4.6mm) for the 3T and 1T scanners, respectively, which did not result in clinically unacceptable plans. Eight of the plans accounting for patient and systematic distortions were deemed clinically unacceptable when assessed on the original CT. For these plans, the mean difference in PTV V95 (volume receiving 95% prescription dose) was 0.13±2.51% and -0.73±1.93% for right- and left-sided patients, respectively. Residual system distortions alone had minimal impact on the dosimetry for the two scanners investigated. The combination of MRI systematic and patient-related distortions can result in unacceptable dosimetry for whole-breast IMRT, a potential issue when considering MRI-only radiotherapy treatment planning. PACS number(s): 87.61.-c, 87.57.cp, 87.57.nj, 87.55.D.
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.|Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|Ingham Institute for Applied Medical Research, Liverpool Hospital, Sydney, NSW, Australia.
authors.forename: Amy
authors.initials: A
authors.lastname: Walker
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.|Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|Ingham Institute for Applied Medical Research, Liverpool Hospital, Sydney, NSW, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Metcalfe
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.|Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|Ingham Institute for Applied Medical Research, Liverpool Hospital, Sydney, NSW, Australia.|Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia.
authors.forename: Gary
authors.initials: G
authors.lastname: Liney
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|Ingham Institute for Applied Medical Research, Liverpool Hospital, Sydney, NSW, Australia.|South Western Clinical School, University of New South Wales, Sydney, NSW, Australia.
authors.forename: Vikneswary
authors.initials: V
authors.lastname: Batumalai
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.|Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|Ingham Institute for Applied Medical Research, Liverpool Hospital, Sydney, NSW, Australia.
authors.forename: Kylie
authors.initials: K
authors.lastname: Dundas
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, MI, USA.
authors.forename: Carri
authors.initials: C
authors.lastname: Glide-Hurst
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|South Western Clinical School, University of New South Wales, Sydney, NSW, Australia.|Collaboration for Cancer Outcomes Research and Evaluation, Liverpool Hospital, Liverpool, NSW, Australia.|School of Medicine, University of Western Sydney, Sydney, NSW, Australia.
authors.forename: Geoff P
authors.initials: GP
authors.lastname: Delaney
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|South Western Clinical School, University of New South Wales, Sydney, NSW, Australia.
authors.forename: Miriam
authors.initials: M
authors.lastname: Boxer
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|Ingham Institute for Applied Medical Research, Liverpool Hospital, Sydney, NSW, Australia.|South Western Clinical School, University of New South Wales, Sydney, NSW, Australia.|Collaboration for Cancer Outcomes Research and Evaluation, Liverpool Hospital, Liverpool, NSW, Australia.|School of Medicine, University of Western Sydney, Sydney, NSW, Australia.
authors.forename: Mei Ling
authors.initials: ML
authors.lastname: Yap
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation Computational Informatics, Australian E-Health Research Centre, Brisbane, Australia.
authors.forename: Jason
authors.initials: J
authors.lastname: Dowling
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation Computational Informatics, Australian E-Health Research Centre, Brisbane, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Rivest-Henault
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.|Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|Ingham Institute for Applied Medical Research, Liverpool Hospital, Sydney, NSW, Australia.
authors.forename: Elise
authors.initials: E
authors.lastname: Pogson
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.|Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.|Ingham Institute for Applied Medical Research, Liverpool Hospital, Sydney, NSW, Australia.|South Western Clinical School, University of New South Wales, Sydney, NSW, Australia.|Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia.
authors.forename: Lois
authors.initials: L
authors.lastname: Holloway
mesh_terms: D001943:Breast Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058958:Organs at Risk / Q000528:radiation effects; D019047:Phantoms, Imaging; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: breast IMRT; geometric distortion; magnetic resonance imaging