Automatic Substitute Computed Tomography Generation and Contouring for Magnetic Resonance Imaging (MRI)-Alone External Beam Radiation Therapy From Standard MRI Sequences.

PURPOSE - To validate automatic substitute computed tomography CT (sCT) scans generated from standard T2-weighted (T2w) magnetic resonance (MR) pelvic scans for MR-Sim prostate treatment planning.

PATIENTS AND METHODS - A Siemens Skyra 3T MR imaging (MRI) scanner with laser bridge, flat couch, and pelvic coil mounts was used to scan 39 patients scheduled for external beam radiation therapy for localized prostate cancer.

For sCT generation a whole-pelvis MRI scan (1. 6 mm 3-dimensional isotropic T2w SPACE [Sampling Perfection with Application optimized Contrasts using different flip angle Evolution] sequence) was acquired. Three additional small field of view scans were acquired: T2w, T2*w, and T1w flip angle 80° for gold fiducials. Patients received a routine planning CT scan. Manual contouring of the prostate, rectum, bladder, and bones was performed independently on the CT and MR scans. Three experienced observers contoured each organ on MRI, allowing interobserver quantification. To generate a training database, each patient CT scan was coregistered to their whole-pelvis T2w using symmetric rigid registration and structure-guided deformable registration. A new multi-atlas local weighted voting method was used to generate automatic contours and sCT results.

RESULTS - The mean error in Hounsfield units between the sCT and corresponding patient CT (within the body contour) was 0. 6 ± 14. 7 (mean ± 1 SD), with a mean absolute error of 40. 5 ± 8. 2 Hounsfield units. Automatic contouring results were very close to the expert interobserver level (Dice similarity coefficient): prostate 0. 80 ± 0. 08, bladder 0. 86 ± 0. 12, rectum 0. 84 ± 0. 06, bones 0. 91 ± 0. 03, and body 1. 00 ± 0. 003. The change in monitor units between the sCT-based plans relative to the gold standard CT plan for the same dose prescription was found to be 0. 3% ± 0. 8%. The 3-dimensional γ pass rate was 1. 00 ± 0. 00 (2 mm/2%).

CONCLUSIONS - The MR-Sim setup and automatic sCT generation methods using standard MR sequences generates realistic contours and electron densities for prostate cancer radiation therapy dose planning and digitally reconstructed radiograph generation.

International journal of radiation oncology, biology, physics. 2015 Sep 05 [Epub]

Jason A Dowling, Jidi Sun, Peter Pichler, David Rivest-Hénault, Soumya Ghose, Haylea Richardson, Chris Wratten, Jarad Martin, Jameen Arm, Leah Best, Shekhar S Chandra, Jurgen Fripp, Frederick W Menk, Peter B Greer

CSIRO Australian e-Health Research Centre, Herston, Queensland, Australia; University of Newcastle, Callaghan, New South Wales, Australia. University of Newcastle, Callaghan, New South Wales, Australia. , Calvary Mater Newcastle Hospital, Waratah, New South Wales, Australia. , CSIRO Australian e-Health Research Centre, Herston, Queensland, Australia. , CSIRO Australian e-Health Research Centre, Herston, Queensland, Australia. , Calvary Mater Newcastle Hospital, Waratah, New South Wales, Australia. , University of Newcastle, Callaghan, New South Wales, Australia; Calvary Mater Newcastle Hospital, Waratah, New South Wales, Australia. , University of Newcastle, Callaghan, New South Wales, Australia; Calvary Mater Newcastle Hospital, Waratah, New South Wales, Australia. , Calvary Mater Newcastle Hospital, Waratah, New South Wales, Australia. , Department of Radiology, Hunter New England Health, New Lambton, New South Wales, Australia. , School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, Queensland, Australia. , CSIRO Australian e-Health Research Centre, Herston, Queensland, Australia. , University of Newcastle, Callaghan, New South Wales, Australia. , University of Newcastle, Callaghan, New South Wales, Australia; Calvary Mater Newcastle Hospital, Waratah, New South Wales, Australia.

PubMed

E-Newsletters

Newsletter subscription

Free Daily and Weekly newsletters offered by content of interest

The fields of GU Oncology and Urology are rapidly advancing. Sign up today for articles, videos, conference highlights and abstracts from peer-review publications by disease and condition delivered to your inbox and read on the go.

Subscribe