title: Usefulness of CT-MRI fusion in radiotherapy planning for localized prostate cancer.
abstract: We compared the prostate volumes and rectal doses calculated by CT and CT-MRI fusion, and verified the usefulness of CT-MRI fusion in three-dimensional (3D) radiotherapy planning for localized prostate cancer. Three observers contoured the prostate and rectum of 13 patients with CT and CT-MRI fusion. Prostate delineations were classified into three sub-parts, and the volumes and distances to the rectum (PR distance) were calculated. 3D radiotherapy plans were generated. A dose-volume histogram (DVH) was constructed for the rectum. The intermodality and interobserver variations were assessed. CT-MRI fusion yielded a significantly lower prostate volume by 31%. In the sub-part analysis, the greatest difference was seen for the apical side. The PR distance was significantly extended by 3.5-mm, and the greatest difference was seen for the basal side. The irradiated rectal volume was reduced in the CT-MRI fusion-based plan. The reduction rates were greater in the relatively high-dose regions. The decrease of the prostate volume and length alteration of the distance between the prostate and rectum were correlated with the decrease of the irradiated rectal volume. The prostate volume delineated by CT-MRI fusion was negatively correlated with the decrease of the irradiated rectal volume. CT showed a tendency towards overestimation of the prostate volume and underestimation of the PR distance as compared to CT-MRI fusion. The rectal dose was significantly reduced in CT-MRI fusion-based plan. Using CT-MRI fusion, especially in cases with a small prostate, the irradiated rectal volume can be reduced, with consequent reduction in rectal complications.
authors.affiliation: Department of Radiology, Gifu University Hospital, Japan. htanaka-gif@umin.ac.jp
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Tanaka
authors.forename: Shinya
authors.initials: S
authors.lastname: Hayashi
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Ohtakara
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Hoshi
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Iida
mesh_terms: D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008297:Male; D011467:Prostate / Q000473:pathology / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D012007:Rectum / Q000473:pathology / Q000528:radiation effects; D014057:Tomography, X-Ray Computed