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Kemppainen R, Suilamo S, Tuokkola T, Lindholm P, Deppe MH, Keyriläinen J. Magnetic resonance-only simulation and dose calculation in external beam radiation therapy: a feasibility study for pelvic cancers. Acta Oncol 2017; 56:792-798. [PMID: 28270011 DOI: 10.1080/0284186x.2017.1293290] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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. MATERIAL AND 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.
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Affiliation(s)
- Reko Kemppainen
- Philips MR Therapy, Vantaa, Finland
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
| | - Sami Suilamo
- Department of Medical Physics, Turku University Hospital, Turku, Finland
- Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Finland
| | - Terhi Tuokkola
- Turku PET-Centre, Turku University Hospital, Finland and University of Turku, Turku, Finland
| | - Paula Lindholm
- Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Finland
| | | | - Jani Keyriläinen
- Department of Medical Physics, Turku University Hospital, Turku, Finland
- Department of Oncology and Radiotherapy, Turku University Hospital, Turku, Finland
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Ginn JS, Agazaryan N, Cao M, Baharom U, Low DA, Yang Y, Gao Y, Hu P, Lee P, Lamb JM. Characterization of spatial distortion in a 0.35 T MRI-guided radiotherapy system. Phys Med Biol 2017; 62:4525-4540. [PMID: 28425431 DOI: 10.1088/1361-6560/aa6e1a] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Spatial distortion results in image deformation that can degrade accurate targeting and dose calculations in MRI-guided adaptive radiotherapy. The authors present a comprehensive assessment of a 0.35 T MRI-guided radiotherapy system's spatial distortion using two commercially-available phantoms with regularly spaced markers. Images of the spatial integrity phantoms were acquired using five clinical protocols on the MRI-guided radiotherapy machine with the radiotherapy gantry positioned at various angles. Software was developed to identify and localize all phantom markers using a template matching approach. Rotational and translational corrections were implemented to account for imperfect phantom alignment. Measurements were made to assess uncertainties arising from susceptibility artifacts, image noise, and phantom construction accuracy. For a clinical 3D imaging protocol with a 1.5 mm reconstructed slice thickness, 100% of spheres within a 50 mm radius of isocenter had a 3D deviation of 1 mm or less. Of the spheres within 100 mm of isocenter, 99.9% had a 3D deviation less than 1 mm. 94.8% and 100% of the spheres within 175 mm were found to be within 1 mm and 2 mm of the expected positions in 3D respectively. Maximum 3D distortions within 50 mm, 100 mm and 175 mm of isocenter were 0.76 mm, 1.15 mm and 1.88 mm respectively. Distortions present in images acquired using the real-time imaging sequence were less than 1 mm for 98.1% and 95.0% of the cylinders within 50 mm and 100 mm of isocenter. The corresponding maximum distortion in these regions was 1.10 mm and 1.67 mm. These results may be used to inform appropriate planning target volume (PTV) margins for 0.35 T MRI-guided radiotherapy. Observed levels of spatial distortion should be explicitly considered when using PTV margins of 3 mm or less or in the case of targets displaced from isocenter by more than 50 mm.
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Affiliation(s)
- John S Ginn
- Department of Radiation Oncology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, United States of America
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Schmidt MA, Wells EJ, Davison K, Riddell AM, Welsh L, Saran F. Stereotactic radiosurgery planning of vestibular schwannomas: Is MRI at 3 Tesla geometrically accurate? Med Phys 2017; 44:375-381. [PMID: 28019663 PMCID: PMC5965671 DOI: 10.1002/mp.12068] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Accepted: 12/14/2016] [Indexed: 11/24/2022] Open
Abstract
Purpose MRI is a mandatory requirement to accurately plan Stereotactic Radiosurgery (SRS) for Vestibular Schwannomas. However, MRI may be distorted due not only to inhomogeneity of the static magnetic field and gradients but also due to susceptibility‐induced effects, which are more prominent at higher magnetic fields. We assess geometrical distortions around air spaces and consider MRI protocol requirements for SRS planning at 3 T. Methods Hardware‐related distortion and the effect of incorrect shimming were investigated with structured test objects. The magnetic field was mapped over the head on five volunteers to assess susceptibility‐related distortion in the naso‐oro‐pharyngeal cavities (NOPC) and around the internal ear canal (IAC). Results Hardware‐related geometric displacements were found to be less than 0.45 mm within the head volume, after distortion correction. Shimming errors can lead to displacements of up to 4 mm, but errors of this magnitude are unlikely to arise in practice. Susceptibility‐related field inhomogeneity was under 3.4 ppm, 2.8 ppm, and 2.7 ppm for the head, NOPC region and IAC region, respectively. For the SRS planning protocol (890 Hz/pixel, approximately 1 mm3 isotropic), susceptibility‐related displacements were less than 0.5 mm (head), and 0.4 mm (IAC and NOPC). Large displacements are possible in MRI examinations undertaken with lower receiver bandwidth values, commonly used in clinical MRI. Higher receiver bandwidth makes the protocol less vulnerable to sub‐optimal shimming. The shimming volume and the CT‐MR co‐registration must be considered jointly. Conclusion Geometric displacements can be kept under 1 mm in the vicinity of air spaces within the head at 3 T with appropriate setting of the receiver bandwidth, correct shimming and employing distortion correction.
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Affiliation(s)
- M A Schmidt
- The Institute of Cancer Research, CR-UK & EPSRC Cancer Imaging Centre, The Royal Marsden NHS Foundation Trust, Sutton, UK
| | - E J Wells
- Medical Physics, Royal Marsden NHS Foundation Trust, London, UK
| | - K Davison
- Radiology Department, Royal Marsden NHS Foundation Trust, London, UK
| | - A M Riddell
- Radiology Department, Royal Marsden NHS Foundation Trust, London, UK
| | - L Welsh
- Neuro-Oncology Unit, Royal Marsden NHS Foundation Trust, London, UK
| | - F Saran
- Neuro-Oncology Unit, Royal Marsden NHS Foundation Trust, London, UK
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Keuschnigg P, Kellner D, Fritscher K, Zechner A, Mayer U, Huber P, Sedlmayer F, Deutschmann H, Steininger P. Nine-degrees-of-freedom flexmap for a cone-beam computed tomography imaging device with independently movable source and detector. Med Phys 2017; 44:132-142. [DOI: 10.1002/mp.12033] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Revised: 11/14/2016] [Accepted: 11/22/2016] [Indexed: 11/09/2022] Open
Affiliation(s)
- Peter Keuschnigg
- Institute for Research and Development on Advanced Radiation Technologies (radART); Paracelsus Medical University; Salzburg Austria
| | - Daniel Kellner
- Institute for Research and Development on Advanced Radiation Technologies (radART); Paracelsus Medical University; Salzburg Austria
- medPhoton GmbH; Salzburg Austria
| | - Karl Fritscher
- medPhoton GmbH; Salzburg Austria
- Division for Biomedical Image Analysis, Department for Biomedical Informatics and Mechatronics; University for Health Sciences, Medical Informatics and Technology (UMIT); Hall in Tyrol Austria
| | | | - Ulrich Mayer
- Institute for Research and Development on Advanced Radiation Technologies (radART); Paracelsus Medical University; Salzburg Austria
- medPhoton GmbH; Salzburg Austria
| | - Philipp Huber
- Institute for Research and Development on Advanced Radiation Technologies (radART); Paracelsus Medical University; Salzburg Austria
| | - Felix Sedlmayer
- Institute for Research and Development on Advanced Radiation Technologies (radART); Paracelsus Medical University; Salzburg Austria
- University Clinic for Radiotherapy and Radio-Oncology, Paracelsus Medical University; Salzburg Austria
| | - Heinz Deutschmann
- Institute for Research and Development on Advanced Radiation Technologies (radART); Paracelsus Medical University; Salzburg Austria
- medPhoton GmbH; Salzburg Austria
- University Clinic for Radiotherapy and Radio-Oncology, Paracelsus Medical University; Salzburg Austria
| | - Philipp Steininger
- Institute for Research and Development on Advanced Radiation Technologies (radART); Paracelsus Medical University; Salzburg Austria
- medPhoton GmbH; Salzburg Austria
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Maspero M, Seevinck PR, Schubert G, Hoesl MAU, van Asselen B, Viergever MA, Lagendijk JJW, Meijer GJ, van den Berg CAT. Quantification of confounding factors in MRI-based dose calculations as applied to prostate IMRT. Phys Med Biol 2017; 62:948-965. [DOI: 10.1088/1361-6560/aa4fe7] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Ito K, Kadoya N, Nakajima Y, Saito M, Sato K, Nagasaka T, Yamanaka K, Dobashi S, Takeda K, Matsushita H, Jingu K. Feasibility of a Direct-Conversion Method from Magnetic Susceptibility to Relative Electron Density for Radiation Therapy Treatment Planning. ACTA ACUST UNITED AC 2017. [DOI: 10.4236/ijmpcero.2017.63023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Stanescu T, Jaffray D. Investigation of the 4D composite MR image distortion field associated with tumor motion for MR-guided radiotherapy. Med Phys 2016; 43:1550-62. [PMID: 26936738 DOI: 10.1118/1.4941958] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
PURPOSE Magnetic resonance (MR) images are affected by geometric distortions due to the specifics of the MR scanner and patient anatomy. Quantifying the distortions associated with mobile tumors is particularly challenging due to real anatomical changes in the tumor's volume, shape, and relative location within the MR imaging volume. In this study, the authors investigate the 4D composite distortion field, which combines the effects of the susceptibility-induced and system-related distortion fields, experienced by mobile lung tumors. METHODS The susceptibility (χ) effects were numerically simulated for two specific scenarios: (a) a full motion cycle of a lung tumor due to breathing as depicted on ten phases of a 4D CBCT data set and (b) varying the tumor size and location in lung tissue via a synthetically generated sphere with variable diameter (4-80 mm). The χ simulation procedure relied on the segmentation and generation of 3D susceptibility (χ) masks and computation of the magnetic field by means of finite difference methods. A system-related distortion field, determined with a phantom and image processing algorithm, was used as a reference. The 4D composite distortion field was generated as the vector summation of the χ-induced and system-related fields. The analysis was performed for two orientations of the main magnetic field (B0), which correspond to several MRIgRT system configurations. Specifically, B0 was set along the z-axis as in the case of a cylindrical-bore scanner and in the (x,y)-plane as for a biplanar MR. Computations were also performed for a full revolution at 15° increments in the case of a rotating biplanar magnet. Histograms and metrics such as maximum, mean, and range were used to evaluate the characteristics of the 4D distortion field. RESULTS The χ-induced field depends on the change in volume and shape of the moving tumor as well as the local surrounding anatomy. In the case of system-related distortions, the tumor experiences increased field perturbations as it moves further away from the MR isocenter. For a mobile lung tumor, the 4D composite field, corresponding to a 1.5 T field and a readout gradient of 5 mT/m, amounts to 3.0 and 2.8 mm for the MRIgRT system designs featuring B0 oriented along the z-axis (cylindrical-bore scanner) and in the (x,y)-plane (biplanar scanner), respectively. For a rotating biplanar scanner, the composite distortion field varied nonlinearly with the rotation angle. Overall, the dominant contribution to the composite field was from the system-related distortion field. The tumor centroid experienced a systematic shift of 2 mm and showed a negligible perturbation for different B0 values. The dependency on the tumor size was also investigated, namely the max values varied from 1.2 to 2.5 mm for spherical volumes with a diameter between 4 and 80 mm. CONCLUSIONS The composite distortion field requires adequate quantification for lung radiation therapy applications such as treatment planning, pretreatment patient setup verification, and real-time treatment delivery guidance. For certain scenarios such as small tumor volumes, the spatial distortions may be corrected by applying systematic shifts derived from a single tumor motion phase. In the case of high readout gradients common to fast imaging applications, the χ distortions were found to be less than 1 mm irrespective of scanner configuration.
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Affiliation(s)
- T Stanescu
- Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario M5G 2M9, Canada and Department of Radiation Oncology, University of Toronto, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada
| | - D Jaffray
- Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario M5G 2M9, Canada and Department of Radiation Oncology, University of Toronto, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada
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Raghavan G, Kishan AU, Cao M, Chen AM. Anatomic and dosimetric changes in patients with head and neck cancer treated with an integrated MRI-tri- 60Co teletherapy device. Br J Radiol 2016; 89:20160624. [PMID: 27653787 DOI: 10.1259/bjr.20160624] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
OBJECTIVE Prior studies have relied on CT to assess alterations in anatomy among patients undergoing radiation for head and neck cancer. We sought to determine the feasibility of using MRI-based image-guided radiotherapy to quantify these changes and to ascertain their potential dosimetric implications. METHODS 6 patients with head and neck cancer were treated with intensity-modulated radiotherapy (IMRT) on a novel tri-60Co teletherapy system equipped with a 0.35-T MRI (VR, ViewRay Incorporated, Oakwood Village, OH) to 66-70 Gy in 33 fractions (fx). Pre-treatment MRIs on Fx 1, 5, 10, 15, 20, 25, 30 and 33 were imported into a contouring interface, where the primary gross tumour volume (GTV) and parotid glands were delineated. The centre of mass (COM) shifts for these structures were assessed relative to Day 1. Dosimetric data were co-registered with the MRIs, and doses to the GTV and parotid glands were assessed. RESULTS Primary GTVs decreased significantly over the course of IMRT (median % volume loss, 38.7%; range, 29.5-72.0%; p < 0.05) at a median rate of 1.2%/fx (range, 0.92-2.2%/fx). Both the ipsilateral and contralateral parotid glands experienced significant volume loss (p < 0.05, for all) and shifted medially during IMRT. Weight loss correlated significantly with parotid gland volume loss and medial COM shift (p < 0.05). CONCLUSION Integrated on-board MRI can be used to accurately contour and analyze primary GTVs and parotid glands over the course of IMRT. COM shifts and significant volume reductions were observed, confirming the results of prior CT-based exercises. Advances in knowledge: The superior resolution of on-board MRI may facilitate online adaptive replanning in the future.
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Affiliation(s)
- Govind Raghavan
- Department of Radiation Oncology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA, USA
| | - Amar U Kishan
- Department of Radiation Oncology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA, USA
| | - Minsong Cao
- Department of Radiation Oncology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA, USA
| | - Allen M Chen
- Department of Radiation Oncology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA, USA
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Pappas EP, Seimenis I, Moutsatsos A, Georgiou E, Nomikos P, Karaiskos P. Characterization of system-related geometric distortions in MR images employed in Gamma Knife radiosurgery applications. Phys Med Biol 2016; 61:6993-7011. [DOI: 10.1088/0031-9155/61/19/6993] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Price RG, Kadbi M, Kim J, Balter J, Chetty IJ, Glide-Hurst CK. Technical Note: Characterization and correction of gradient nonlinearity induced distortion on a 1.0 T open bore MR-SIM. Med Phys 2016; 42:5955-60. [PMID: 26429270 DOI: 10.1118/1.4930245] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Distortions in magnetic resonance imaging (MRI) compromise spatial fidelity, potentially impacting delineation and dose calculation. We characterized 2D and 3D large field of view (FOV), sequence-independent distortion at various positions in a 1.0 T high-field open MR simulator (MR-SIM) to implement correction maps for MRI treatment planning. METHODS A 36 × 43 × 2 cm(3) phantom with 255 known landmarks (∼1 mm(3)) was scanned using 1.0 T high-field open MR-SIM at isocenter in the transverse, sagittal, and coronal axes, and a 465 × 350 × 168 mm(3) 3D phantom was scanned by stepping in the superior-inferior direction in three overlapping positions to achieve a total 465 × 350 × 400 mm(3) sampled FOV yielding >13 800 landmarks (3D Gradient-Echo, TE/TR/α = 5.54 ms/30 ms/28°, voxel size = 1 × 1 × 2 mm(3)). A binary template (reference) was generated from a phantom schematic. An automated program converted MR images to binary via masking, thresholding, and testing for connectivity to identify landmarks. Distortion maps were generated by centroid mapping. Images were corrected via warping with inverse distortion maps, and temporal stability was assessed. RESULTS Over the sampled FOV, non-negligible residual gradient distortions existed as close as 9.5 cm from isocenter, with a maximum distortion of 7.4 mm as close as 23 cm from isocenter. Over six months, average gradient distortions were -0.07 ± 1.10 mm and 0.10 ± 1.10 mm in the x and y directions for the transverse plane, 0.03 ± 0.64 and -0.09 ± 0.70 mm in the sagittal plane, and 0.4 ± 1.16 and 0.04 ± 0.40 mm in the coronal plane. After implementing 3D correction maps, distortions were reduced to <1 pixel width (1 mm) for all voxels up to 25 cm from magnet isocenter. CONCLUSIONS Inherent distortion due to gradient nonlinearity was found to be non-negligible even with vendor corrections applied, and further corrections are required to obtain 1 mm accuracy for large FOVs. Statistical analysis of temporal stability shows that sequence independent distortion maps are consistent within six months of characterization.
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Affiliation(s)
- Ryan G Price
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan 48202 and Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Mo Kadbi
- Philips Healthcare, Cleveland, Ohio 44143
| | - Joshua Kim
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan 48202
| | - James Balter
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Indrin J Chetty
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan 48202 and Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Carri K Glide-Hurst
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan 48202 and Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, Michigan 48201
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Ghose S, Mitra J, Rivest-Hénault D, Fazlollahi A, Stanwell P, Pichler P, Sun J, Fripp J, Greer PB, Dowling JA. MRI-alone radiation therapy planning for prostate cancer: Automatic fiducial marker detection. Med Phys 2016; 43:2218. [DOI: 10.1118/1.4944871] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Price RG, Kim JP, Zheng W, Chetty IJ, Glide-Hurst C. Image Guided Radiation Therapy Using Synthetic Computed Tomography Images in Brain Cancer. Int J Radiat Oncol Biol Phys 2016; 95:1281-9. [PMID: 27209500 DOI: 10.1016/j.ijrobp.2016.03.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Revised: 02/26/2016] [Accepted: 03/03/2016] [Indexed: 12/01/2022]
Abstract
PURPOSE The development of synthetic computed tomography (CT) (synCT) derived from magnetic resonance (MR) images supports MR-only treatment planning. We evaluated the accuracy of synCT and synCT-generated digitally reconstructed radiographs (DRRs) relative to CT and determined their performance for image guided radiation therapy (IGRT). METHODS AND MATERIALS Magnetic resonance simulation (MR-SIM) and CT simulation (CT-SIM) images were acquired of an anthropomorphic skull phantom and 12 patient brain cancer cases. SynCTs were generated using fluid attenuation inversion recovery, ultrashort echo time, and Dixon data sets through a voxel-based weighted summation of 5 tissue classifications. The DRRs were generated from the phantom synCT, and geometric fidelity was assessed relative to CT-generated DRRs through bounding box and landmark analysis. An offline retrospective analysis was conducted to register cone beam CTs (n=34) to synCTs and CTs using automated rigid registration in the treatment planning system. Planar MV and KV images (n=37) were rigidly registered to synCT and CT DRRs using an in-house script. Planar and volumetric registration reproducibility was assessed and margin differences were characterized by the van Herk formalism. RESULTS Bounding box and landmark analysis of phantom synCT DRRs were within 1 mm of CT DRRs. Absolute planar registration shift differences ranged from 0.0 to 0.7 mm for phantom DRRs on all treatment platforms and from 0.0 to 0.4 mm for volumetric registrations. For patient planar registrations, the mean shift differences were 0.4 ± 0.5 mm (range, -0.6 to 1.6 mm), 0.0 ± 0.5 mm (range, -0.9 to 1.2 mm), and 0.1 ± 0.3 mm (range, -0.7 to 0.6 mm) for the superior-inferior (S-I), left-right (L-R), and anterior-posterior (A-P) axes, respectively. The mean shift differences in volumetric registrations were 0.6 ± 0.4 mm (range, -0.2 to 1.6 mm), 0.2 ± 0.4 mm (range, -0.3 to 1.2 mm), and 0.2 ± 0.3 mm (range, -0.2 to 1.2 mm) for the S-I, L-R, and A-P axes, respectively. The CT-SIM and synCT derived margins were <0.3 mm different. CONCLUSION DRRs generated by synCT were in close agreement with CT-SIM. Planar and volumetric image registrations to synCT-derived targets were comparable with CT for phantom and patients. This validation is the next step toward MR-only planning for the brain.
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Affiliation(s)
- Ryan G Price
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan; Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, Michigan
| | - Joshua P Kim
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan
| | - Weili Zheng
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan
| | - Indrin J Chetty
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan; Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, Michigan
| | - Carri Glide-Hurst
- Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan; Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, Michigan.
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Weygand J, Fuller CD, Ibbott GS, Mohamed ASR, Ding Y, Yang J, Hwang KP, Wang J. Spatial Precision in Magnetic Resonance Imaging-Guided Radiation Therapy: The Role of Geometric Distortion. Int J Radiat Oncol Biol Phys 2016; 95:1304-16. [PMID: 27354136 DOI: 10.1016/j.ijrobp.2016.02.059] [Citation(s) in RCA: 113] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Revised: 02/05/2016] [Accepted: 02/25/2016] [Indexed: 12/11/2022]
Abstract
Because magnetic resonance imaging-guided radiation therapy (MRIgRT) offers exquisite soft tissue contrast and the ability to image tissues in arbitrary planes, the interest in this technology has increased dramatically in recent years. However, intrinsic geometric distortion stemming from both the system hardware and the magnetic properties of the patient affects MR images and compromises the spatial integrity of MRI-based radiation treatment planning, given that for real-time MRIgRT, precision within 2 mm is desired. In this article, we discuss the causes of geometric distortion, describe some well-known distortion correction algorithms, and review geometric distortion measurements from 12 studies, while taking into account relevant imaging parameters. Eleven of the studies reported phantom measurements quantifying system-dependent geometric distortion, while 2 studies reported simulation data quantifying magnetic susceptibility-induced geometric distortion. Of the 11 studies investigating system-dependent geometric distortion, 5 reported maximum measurements less than 2 mm. The simulation studies demonstrated that magnetic susceptibility-induced distortion is typically smaller than system-dependent distortion but still nonnegligible, with maximum distortion ranging from 2.1 to 2.6 mm at a field strength of 1.5 T. As expected, anatomic landmarks containing interfaces between air and soft tissue had the largest distortions. The evidence indicates that geometric distortion reduces the spatial integrity of MRI-based radiation treatment planning and likely diminishes the efficacy of MRIgRT. Better phantom measurement techniques and more effective distortion correction algorithms are needed to achieve the desired spatial precision.
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Affiliation(s)
- Joseph Weygand
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas.
| | - Clifton David Fuller
- The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas; Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas
| | - Geoffrey S Ibbott
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas
| | - Abdallah S R Mohamed
- Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas; Department of Clinical Oncology and Nuclear Medicine, Alexandria University, Alexandria, Egypt
| | - Yao Ding
- Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas
| | - Jinzhong Yang
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas
| | - Ken-Pin Hwang
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas
| | - Jihong Wang
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas
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Walker A, Liney G, Holloway L, Dowling J, Rivest-Henault D, Metcalfe P. Continuous table acquisition MRI for radiotherapy treatment planning: distortion assessment with a new extended 3D volumetric phantom. Med Phys 2015; 42:1982-91. [PMID: 25832089 DOI: 10.1118/1.4915920] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Accurate geometry is required for radiotherapy treatment planning (RTP). When considering the use of magnetic resonance imaging (MRI) for RTP, geometric distortions observed in the acquired images should be considered. While scanner technology and vendor supplied correction algorithms provide some correction, large distortions are still present in images, even when considering considerably smaller scan lengths than those typically acquired with CT in conventional RTP. This study investigates MRI acquisition with a moving table compared with static scans for potential geometric benefits for RTP. METHODS A full field of view (FOV) phantom (diameter 500 mm; length 513 mm) was developed for measuring geometric distortions in MR images over volumes pertinent to RTP. The phantom consisted of layers of refined plastic within which vitamin E capsules were inserted. The phantom was scanned on CT to provide the geometric gold standard and on MRI, with differences in capsule location determining the distortion. MRI images were acquired with two techniques. For the first method, standard static table acquisitions were considered. Both 2D and 3D acquisition techniques were investigated. With the second technique, images were acquired with a moving table. The same sequence was acquired with a static table and then with table speeds of 1.1 mm/s and 2 mm/s. All of the MR images acquired were registered to the CT dataset using a deformable B-spline registration with the resulting deformation fields providing the distortion information for each acquisition. RESULTS MR images acquired with the moving table enabled imaging of the whole phantom length while images acquired with a static table were only able to image 50%-70% of the phantom length of 513 mm. Maximum distortion values were reduced across a larger volume when imaging with a moving table. Increased table speed resulted in a larger contribution of distortion from gradient nonlinearities in the through-plane direction and an increased blurring of capsule images, resulting in an apparent capsule volume increase by up to 170% in extreme axial FOV regions. Blurring increased with table speed and in the central regions of the phantom, geometric distortion was less for static table acquisitions compared to a table speed of 2 mm/s over the same volume. Overall, the best geometric accuracy was achieved with a table speed of 1.1 mm/s. CONCLUSIONS The phantom designed enables full FOV imaging for distortion assessment for the purposes of RTP. MRI acquisition with a moving table extends the imaging volume in the z direction with reduced distortions which could be useful particularly if considering MR-only planning. If utilizing MR images to provide additional soft tissue information to the planning CT, standard acquisition sequences over a smaller volume would avoid introducing additional blurring or distortions from the through-plane table movement.
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Affiliation(s)
- Amy Walker
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia and Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia
| | - Gary Liney
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia; Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia; and South West Clinical School, University of New South Wales, Sydney, NSW 2170, Australia
| | - Lois Holloway
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia; Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia; South West Clinical School, University of New South Wales, Sydney, NSW 2170, Australia; and Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW 2006, Australia
| | - Jason Dowling
- Commonwealth Scientific and Industrial Research Organisation, Australian E-Health Research Centre, Herston, QLD 4029, Australia
| | - David Rivest-Henault
- Commonwealth Scientific and Industrial Research Organisation, Australian E-Health Research Centre, Herston, QLD 4029, Australia
| | - Peter Metcalfe
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia and Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute for Applied Medical Research, Liverpool, NSW 2170, Australia
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Abstract
The use of magnetic resonance imaging (MRI) in radiotherapy (RT) planning is rapidly expanding. We review the wide range of image contrast mechanisms available to MRI and the way they are exploited for RT planning. However a number of challenges are also considered: the requirements that MR images are acquired in the RT treatment position, that they are geometrically accurate, that effects of patient motion during the scan are minimized, that tissue markers are clearly demonstrated, that an estimate of electron density can be obtained. These issues are discussed in detail, prior to the consideration of a number of specific clinical applications. This is followed by a brief discussion on the development of real-time MRI-guided RT.
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Affiliation(s)
- Maria A Schmidt
- Cancer Research UK Cancer Imaging Centre, Royal Marsden Hospital and the Institute of Cancer Research, Downs Road, Sutton, Surrey, SM2 5PT, UK
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66
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Magnetic resonance imaging-guided brachytherapy for cervical cancer: initiating a program. J Contemp Brachytherapy 2015; 7:417-22. [PMID: 26622249 PMCID: PMC4663219 DOI: 10.5114/jcb.2015.55541] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Accepted: 10/30/2015] [Indexed: 11/17/2022] Open
Abstract
Over the past decade, the application of magnetic resonance imaging (MRI) has increased, and there is growing evidence to suggest that improvements in accuracy of target delineation in MRI-guided brachytherapy may improve clinical outcomes in cervical cancer. To implement a high quality image guided brachytherapy program, a multidisciplinary team is required with appropriate expertise as well as an adequate patient load to ensure a sustainable program. It is imperative to know that the most important source of uncertainty in the treatment process is related to target delineation and therefore, the necessity of training and expertise as well as quality assurance should be emphasized. A short review of concepts and techniques that have been developed for implementation and/or improvement of workflow of a MRI-guided brachytherapy program are provided in this document, so that institutions can use and optimize some of them based on their resources to minimize their procedure times.
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Siversson C, Nordström F, Nilsson T, Nyholm T, Jonsson J, Gunnlaugsson A, Olsson LE. Technical Note: MRI only prostate radiotherapy planning using the statistical decomposition algorithm. Med Phys 2015; 42:6090-7. [DOI: 10.1118/1.4931417] [Citation(s) in RCA: 103] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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Converting from CT- to MRI-only-based target definition in radiotherapy of localized prostate cancer. Strahlenther Onkol 2015; 191:862-8. [DOI: 10.1007/s00066-015-0868-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 06/12/2015] [Indexed: 11/30/2022]
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Extensive pneumatized air cells causing susceptibility artifacts in the petrosus part of the ICA. Clin Neuroradiol 2015; 27:91-96. [PMID: 25939527 DOI: 10.1007/s00062-015-0392-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 04/08/2015] [Indexed: 01/14/2023]
Abstract
INTRODUCTION 3D-Time-of-flight magnetic-resonance-angiography (TOF MRA) is an established method in vessel analysis. However, many artifacts that occur may lead to a false diagnosis. This retrospective study evaluates the coherence of MR artifacts to extensive pneumatized air cells surrounding the internal carotid artery (ICA) in the petrosus part of the temporal bone. MATERIALS AND METHODS Patients who received 3D-TOF MRA and multidetector helical computed tomography (CT) angiography were registered from April 2012 to April 2013. Of these patients, both ICAs in the petrosus part were analyzed. Vertical maximum intensity projection (MIP) artifacts were graduated as normal, mild to moderate, and severe artifacts. The distinction of the vertical part of the pneumatized air cells was also categorized in three groups, regarding the circumference of the ICA in pneumatization ≤ 90°, between 90° and 180°, and ≥ 180°. RESULTS A total of 203 vessels were collected for analysis. The more extensive the pneumatized air cells were present, the more band-like artifacts and pseudostenosis at the vertical portion of the petrosus part of the ICA were registered. CONCLUSION Careful examination of the source images and evaluation of the size of the pneumatized air cells with CT scan are essential to avoid false positive diagnosis in the distal petrosus part of the ICA.
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Doemer A, Chetty IJ, Glide-Hurst C, Nurushev T, Hearshen D, Pantelic M, Traughber M, Kim J, Levin K, Elshaikh MA, Walker E, Movsas B. Evaluating organ delineation, dose calculation and daily localization in an open-MRI simulation workflow for prostate cancer patients. Radiat Oncol 2015; 10:37. [PMID: 25889107 PMCID: PMC4340286 DOI: 10.1186/s13014-014-0309-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Accepted: 12/15/2014] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND This study describes initial testing and evaluation of a vertical-field open Magnetic Resonance Imaging (MRI) scanner for the purpose of simulation in radiation therapy for prostate cancer. We have evaluated the clinical workflow of using open MRI as a sole modality for simulation and planning. Relevant results related to MRI alignment (vs. CT) reference dataset with Cone-Beam CT (CBCT) for daily localization are presented. METHODS Ten patients participated in an IRB approved study utilizing MRI along with CT simulation with the intent of evaluating the MRI-simulation process. Differences in prostate gland volume, seminal vesicles, and penile bulb were assessed with MRI and compared to CT. To evaluate dose calculation accuracy, bulk-density-assignments were mapped onto respective MRI datasets and treated IMRT plans were re-calculated. For image localization purposes, 400 CBCTs were re-evaluated with MRI as the reference dataset and daily shifts compared against CBCT-to-CT registration. Planning margins based on MRI/CBCT shifts were computed using the van Herk formalism. RESULTS Significant organ contour differences were noted between MRI and CT. Prostate volumes were on average 39.7% (p = 0.002) larger on CT than MRI. No significant difference was found in seminal vesicle volumes (p = 0.454). Penile bulb volumes were 61.1% higher on CT, without statistical significance (p = 0.074). MRI-based dose calculations with assigned bulk densities produced agreement within 1% with heterogeneity corrected CT calculations. The differences in shift positions for the cohort between CBCT-to-CT registration and CBCT-to-MRI registration are -0.15 ± 0.25 cm (anterior-posterior), 0.05 ± 0.19 cm (superior-inferior), and -0.01 ± 0.14 cm (left-right). CONCLUSIONS This study confirms the potential of using an open-field MRI scanner as primary imaging modality for prostate cancer treatment planning simulation, dose calculations and daily image localization.
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Affiliation(s)
- Anthony Doemer
- Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | - Indrin J Chetty
- Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | - Carri Glide-Hurst
- Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | - Teamour Nurushev
- Department of Radiation Oncology, 21st Century Oncology, 28585 Orchard Lake Rd, Suite 110, Farmington Hills, MI, 48334, USA.
| | - David Hearshen
- Department of Radiology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | - Milan Pantelic
- Department of Radiology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | | | - Joshua Kim
- Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | - Kenneth Levin
- Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | - Mohamed A Elshaikh
- Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | - Eleanor Walker
- Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
| | - Benjamin Movsas
- Department of Radiation Oncology, Henry Ford Health System, 2799 W. Grand Blvd, Detroit, MI, 48202, USA.
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Tanderup K, Viswanathan AN, Kirisits C, Frank SJ. Magnetic resonance image guided brachytherapy. Semin Radiat Oncol 2015; 24:181-91. [PMID: 24931089 DOI: 10.1016/j.semradonc.2014.02.007] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The application of magnetic resonance image (MRI)-guided brachytherapy has demonstrated significant growth during the past 2 decades. Clinical improvements in cervix cancer outcomes have been linked to the application of repeated MRI for identification of residual tumor volumes during radiotherapy. This has changed clinical practice in the direction of individualized dose administration, and resulted in mounting evidence of improved clinical outcome regarding local control, overall survival as well as morbidity. MRI-guided prostate high-dose-rate and low-dose-rate brachytherapies have improved the accuracy of target and organs-at-risk delineation, and the potential exists for improved dose prescription and reporting for the prostate gland and organs at risk. Furthermore, MRI-guided prostate brachytherapy has significant potential to identify prostate subvolumes and dominant lesions to allow for dose administration reflecting the differential risk of recurrence. MRI-guided brachytherapy involves advanced imaging, target concepts, and dose planning. The key issue for safe dissemination and implementation of high-quality MRI-guided brachytherapy is establishment of qualified multidisciplinary teams and strategies for training and education.
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Affiliation(s)
- Kari Tanderup
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO; Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.
| | - Akila N Viswanathan
- Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women׳s Hospital, Boston, MA
| | - Christian Kirisits
- Department of Radiotherapy, Comprehensive Cancer Center and Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Vienna, Austria
| | - Steven J Frank
- Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX
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72
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Mutic S, Dempsey JF. The ViewRay system: magnetic resonance-guided and controlled radiotherapy. Semin Radiat Oncol 2015; 24:196-9. [PMID: 24931092 DOI: 10.1016/j.semradonc.2014.02.008] [Citation(s) in RCA: 677] [Impact Index Per Article: 75.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
A description of the first commercially available magnetic resonance imaging (MRI)-guided radiation therapy (RT) system is provided. The system consists of a split 0.35-T MR scanner straddling 3 (60)Co heads mounted on a ring gantry, each head equipped with independent doubly focused multileaf collimators. The MR and RT systems share a common isocenter, enabling simultaneous and continuous MRI during RT delivery. An on-couch adaptive RT treatment-planning system and integrated MRI-guided RT control system allow for rapid adaptive planning and beam delivery control based on the visualization of soft tissues. Treatment of patients with this system commenced at Washington University in January 2014.
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Affiliation(s)
- Sasa Mutic
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO.
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73
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Uh J, Merchant TE, Li Y, Li X, Hua C. MRI-based treatment planning with pseudo CT generated through atlas registration. Med Phys 2014; 41:051711. [PMID: 24784377 DOI: 10.1118/1.4873315] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To evaluate the feasibility and accuracy of magnetic resonance imaging (MRI)-based treatment planning using pseudo CTs generated through atlas registration. METHODS A pseudo CT, providing electron density information for dose calculation, was generated by deforming atlas CT images previously acquired on other patients. The authors tested 4 schemes of synthesizing a pseudo CT from single or multiple deformed atlas images: use of a single arbitrarily selected atlas, arithmetic mean process using 6 atlases, and pattern recognition with Gaussian process (PRGP) using 6 or 12 atlases. The required deformation for atlas CT images was derived from a nonlinear registration of conjugated atlas MR images to that of the patient of interest. The contrasts of atlas MR images were adjusted by histogram matching to reduce the effect of different sets of acquisition parameters. For comparison, the authors also tested a simple scheme assigning the Hounsfield unit of water to the entire patient volume. All pseudo CT generating schemes were applied to 14 patients with common pediatric brain tumors. The image similarity of real patient-specific CT and pseudo CTs constructed by different schemes was compared. Differences in computation times were also calculated. The real CT in the treatment planning system was replaced with the pseudo CT, and the dose distribution was recalculated to determine the difference. RESULTS The atlas approach generally performed better than assigning a bulk CT number to the entire patient volume. Comparing atlas-based schemes, those using multiple atlases outperformed the single atlas scheme. For multiple atlas schemes, the pseudo CTs were similar to the real CTs (correlation coefficient, 0.787-0.819). The calculated dose distribution was in close agreement with the original dose. Nearly the entire patient volume (98.3%-98.7%) satisfied the criteria of chi-evaluation (<2% maximum dose and 2 mm range). The dose to 95% of the volume and the percentage of volume receiving at least 95% of the prescription dose in the planning target volume differed from the original values by less than 2% of the prescription dose (root-mean-square, RMS < 1%). The PRGP scheme did not perform better than the arithmetic mean process with the same number of atlases. Increasing the number of atlases from 6 to 12 often resulted in improvements, but statistical significance was not always found. CONCLUSIONS MRI-based treatment planning with pseudo CTs generated through atlas registration is feasible for pediatric brain tumor patients. The doses calculated from pseudo CTs agreed well with those from real CTs, showing dosimetric accuracy within 2% for the PTV when multiple atlases were used. The arithmetic mean process may be a reasonable choice over PRGP for the synthesis scheme considering performance and computational costs.
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Affiliation(s)
- Jinsoo Uh
- Department of Radiological Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee 38105
| | - Thomas E Merchant
- Department of Radiological Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee 38105
| | - Yimei Li
- Department of Biostatistics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105
| | - Xingyu Li
- Department of Biostatistics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105
| | - Chiaho Hua
- Department of Radiological Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee 38105
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Tadic T, Jaffray DA, Stanescu T. Harmonic analysis for the characterization and correction of geometric distortion in MRI. Med Phys 2014; 41:112303. [DOI: 10.1118/1.4898582] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Lagendijk JJW, Raaymakers BW, Van den Berg CAT, Moerland MA, Philippens ME, van Vulpen M. MR guidance in radiotherapy. Phys Med Biol 2014; 59:R349-69. [PMID: 25322150 DOI: 10.1088/0031-9155/59/21/r349] [Citation(s) in RCA: 153] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Jan J W Lagendijk
- Department of Radiotherapy, University Medical Centre Utrecht, Heidelberglaan 100, Utrecht, The Netherlands
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Chin AL, Lin A, Anamalayil S, Teo BKK. Feasibility and limitations of bulk density assignment in MRI for head and neck IMRT treatment planning. J Appl Clin Med Phys 2014; 15:4851. [PMID: 25207571 PMCID: PMC5711084 DOI: 10.1120/jacmp.v15i5.4851] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Revised: 05/08/2014] [Accepted: 04/30/2014] [Indexed: 12/04/2022] Open
Abstract
Head and neck cancers centered at the base of skull are better visualized on MRI than on CT. The purpose of this investigation was to investigate the accuracy of bulk density assignment in head and neck intensity‐modulated radiation therapy (IMRT) treatment plan optimization. Our study investigates dose calculation differences between density‐assigned MRI and CT, and identifies potential limitations related to dental implants and MRI geometrical distortion in the framework of MRI‐only‐based treatment planning. Bulk density assignment was performed and applied onto MRI to generate three MRI image sets with increasing levels of heterogeneity for seven patients: 1) MRIW: all water‐equivalent; 2) MRIW + B: included bone with density of 1.53 g/cm3; and 3) MRIW + B + A: included bone and air. Using identical planning and optimization parameters, MRI‐based IMRT plans were generated and compared to corresponding, forward‐calculated, CT‐based plans on the basis of target coverage, isodose distributions, and dose‐volume histograms (DVHs). Phantom studies were performed to assess the magnitude and spatial dependence of MRI geometrical distortion. MRIW‐based dose calculations overestimated target coverage by 16.1%. Segmentation of bone reduced differences to within 2% of the coverage area on the CT‐based plan. Further segmentation of air improved conformity near air–tissue interfaces. Dental artifacts caused substantial target coverage overestimation even on MRIW + B + A. Geometrical distortion was less than 1 mm in an imaging volume 20 × 20 × 20 cm3 around scanner isocenter, but up to 4 mm at 17 cm lateral to isocenter. Bulk density assignment in the framework of MRI‐only IMRT head and neck treatment planning is a feasible method with certain limitations. Bone and teeth account for the majority of density heterogeneity effects. While soft tissue is well visualized on MRI compared to CT, dental implants may not be visible on MRI and must be identified by other means and assigned appropriate density for accurate dose calculation. Far off‐center geometrical distortion of the body contour near the shoulder region is a potential source of dose calculation inaccuracy. PACS numbers: 87.61.‐c, 87.55.‐D
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77
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Korhonen J, Kapanen M, Keyriläinen J, Seppälä T, Tenhunen M. A dual model HU conversion from MRI intensity values within and outside of bone segment for MRI-based radiotherapy treatment planning of prostate cancer. Med Phys 2014; 41:011704. [PMID: 24387496 DOI: 10.1118/1.4842575] [Citation(s) in RCA: 121] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The lack of electron density information in magnetic resonance images (MRI) poses a major challenge for MRI-based radiotherapy treatment planning (RTP). In this study the authors convert MRI intensity values into Hounsfield units (HUs) in the male pelvis and thus enable accurate MRI-based RTP for prostate cancer patients with varying tissue anatomy and body fat contents. METHODS T1/T2*-weighted MRI intensity values and standard computed tomography (CT) image HUs in the male pelvis were analyzed using image data of 10 prostate cancer patients. The collected data were utilized to generate a dual model HU conversion technique from MRI intensity values of the single image set separately within and outside of contoured pelvic bones. Within the bone segment local MRI intensity values were converted to HUs by applying a second-order polynomial model. This model was tuned for each patient by two patient-specific adjustments: MR signal normalization to correct shifts in absolute intensity level and application of a cutoff value to accurately represent low density bony tissue HUs. For soft tissues, such as fat and muscle, located outside of the bone contours, a threshold-based segmentation method without requirements for any patient-specific adjustments was introduced to convert MRI intensity values into HUs. The dual model HU conversion technique was implemented by constructing pseudo-CT images for 10 other prostate cancer patients. The feasibility of these images for RTP was evaluated by comparing HUs in the generated pseudo-CT images with those in standard CT images, and by determining deviations in MRI-based dose distributions compared to those in CT images with 7-field intensity modulated radiation therapy (IMRT) with the anisotropic analytical algorithm and 360° volumetric-modulated arc therapy (VMAT) with the Voxel Monte Carlo algorithm. RESULTS The average HU differences between the constructed pseudo-CT images and standard CT images of each test patient ranged from -2 to 5 HUs and from 22 to 78 HUs in soft and bony tissues, respectively. The average local absolute value differences were 11 HUs in soft tissues and 99 HUs in bones. The planning target volume doses (volumes 95%, 50%, 5%) in the pseudo-CT images were within 0.8% compared to those in CT images in all of the 20 treatment plans. The average deviation was 0.3%. With all the test patients over 94% (IMRT) and 92% (VMAT) of dose points within body (lower than 10% of maximum dose suppressed) passed the 1 mm and 1% 2D gamma index criterion. The statistical tests (t- and F-tests) showed significantly improved (p ≤ 0.05) HU and dose calculation accuracies with the soft tissue conversion method instead of homogeneous representation of these tissues in MRI-based RTP images. CONCLUSIONS This study indicates that it is possible to construct high quality pseudo-CT images by converting the intensity values of a single MRI series into HUs in the male pelvis, and to use these images for accurate MRI-based prostate RTP dose calculations.
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Affiliation(s)
- Juha Korhonen
- Clinical Research Institute Helsinki University Central Hospital Ltd., POB-700, 00029 HUS, Finland and Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS, Finland
| | - Mika Kapanen
- Clinical Research Institute Helsinki University Central Hospital Ltd., POB-700, 00029 HUS, Finland; Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS, Finland; and Department of Medical Physics, Tampere University Hospital, POB-2000, 33521 Tampere, Finland
| | - Jani Keyriläinen
- Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS, Finland
| | - Tiina Seppälä
- Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS, Finland
| | - Mikko Tenhunen
- Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS, Finland
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Korhonen J, Kapanen M, Keyriläinen J, Seppälä T, Tuomikoski L, Tenhunen M. Influence of MRI-based bone outline definition errors on external radiotherapy dose calculation accuracy in heterogeneous pseudo-CT images of prostate cancer patients. Acta Oncol 2014; 53:1100-6. [PMID: 24998163 DOI: 10.3109/0284186x.2014.929737] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
BACKGROUND This work evaluates influences of susceptibility-induced bone outline shift and perturbations, and bone segmentation errors on external radiotherapy dose calculation accuracy in magnetic resonance imaging (MRI)-based pseudo-computed tomography (CT) images of the male pelvis. MATERIAL AND METHODS T₁/T₂*-weighted fast gradient echo, T₁-weighted spin echo and T₂-weighted fast spin echo images were used in bone detection investigation. Bone edge location and bone diameter in MRI were evaluated by comparing those in the images with actual physical measurements of fresh deer bones positioned in a gelatine phantom. Dose calculation accuracy in pseudo-CT images was investigated for 15 prostate cancer patients. Bone outlines in T₁/T₂*-weighted images were contoured and additional segmentation errors were simulated by expanding and contracting the bone contours with 1 mm spacing. Heterogeneous pseudo-CT images were constructed by adopting a technique transforming the MRI intensity values into Hounsfield units with separate conversion models within and outside of bone segment. RESULTS Bone edges and diameter in the phantom were illustrated correctly within a 1 mm-pixel size in MRI. Each 1 mm-sized systematic error in bone segment resulted in roughly 0.4% change to the prostate dose level in the pseudo-CT images. The prostate average (range) dose levels in pseudo-CT images with additional systematic bone segmentation errors of -2 mm, 0 mm and 2 mm were 0.5% (-0.5-1.4%), -0.2% (-1.0-0.7%), and -0.9% (-1.8-0.0%) compared to those in CT images, respectively, in volumetric modulated arc therapy treatment plans calculated by Monte Carlo algorithm. CONCLUSIONS Susceptibility-induced bone outline shift and perturbations do not result in substantial uncertainty for MRI-based dose calculation. Dose consistency of 2% can be achieved reliably for the prostate if heterogeneous pseudo-CT images are constructed with ≤± 2 mm systematic error in bone segment.
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Affiliation(s)
- Juha Korhonen
- Clinical Research Institute Helsinki University Central Hospital Ltd , Helsinki , Finland
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