title: Comparison of User-Directed and Automatic Mapping of the Planned Isocenter to Treatment Space for Prostate IGRT.
abstract: Image-guided radiotherapy (IGRT), adaptive radiotherapy (ART), and online reoptimization rely on accurate mapping of the radiation beam isocenter(s) from planning to treatment space. This mapping involves rigid and/or nonrigid registration of planning (pCT) and intratreatment (tCT) CT images. The purpose of this study was to retrospectively compare a fully automatic approach, including a non-rigid step, against a user-directed rigid method implemented in a clinical IGRT protocol for prostate cancer. Isocenters resulting from automatic and clinical mappings were compared to reference isocenters carefully determined in each tCT. Comparison was based on displacements from the reference isocenters and prostate dose-volume histograms (DVHs). Ten patients with a total of 243 tCTs were investigated. Fully automatic registration was found to be as accurate as the clinical protocol but more precise for all patients. The average of the unsigned x, y, and z offsets and the standard deviations ( σ ) of the signed offsets computed over all images were (avg. ±   σ  (mm)): 1.1 ± 1.4, 1.8 ± 2.3, 2.5 ± 3.5 for the clinical protocol and 0.6 ± 0.8, 1.1 ± 1.5 and 1.1 ± 1.4 for the automatic method. No failures or outliers from automatic mapping were observed, while 8 outliers occurred for the clinical protocol.
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA.
authors.forename: Zijie
authors.initials: Z
authors.lastname: Xu
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA.
authors.forename: Ronald
authors.initials: R
authors.lastname: Chen
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kress
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA ; Morphormics, Inc., 240 Leigh Farm Road, Durham, NC 27707, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Foskey
authors.affiliation: Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI, USA.
authors.forename: An
authors.initials: A
authors.lastname: Qin
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA.
authors.forename: Timothy
authors.initials: T
authors.lastname: Cullip
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA.
authors.forename: Gregg
authors.initials: G
authors.lastname: Tracton
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA.
authors.forename: Sha
authors.initials: S
authors.lastname: Chang
authors.affiliation: Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI, USA.
authors.forename: Joel
authors.initials: J
authors.lastname: Tepper
authors.affiliation: Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI, USA.
authors.forename: Di
authors.initials: D
authors.lastname: Yan
authors.affiliation: Department of Radiation Oncology, CB 7512, University of North Carolina, Chapel Hill, NC 27599 7512, USA ; Morphormics, Inc., 240 Leigh Farm Road, Durham, NC 27707, USA.
authors.forename: Edward
authors.initials: E
authors.lastname: Chaney