title: Analysis of Prostate Deformation during a Course of Radiation Therapy for Prostate Cancer.
abstract: OBJECTIVE
  Accurate analysis of the correlation between deformation of the prostate and displacement of its center of gravity (CoG) is important for efficient radiation therapy for prostate cancer. In this study, we addressed this problem by introducing a new analysis approach.
  
  
  METHODS
  A planning computed tomography (CT) scan and 7 repeat cone-beam CT scans during the course of treatment were obtained for 19 prostate cancer patients who underwent three-dimensional conformal radiation therapy. A single observer contoured the prostate gland only. To evaluate the local deformation of the prostate, it was divided into 12 manually defined segments. Prostate deformation was calculated using in-house developed software. The correlation between the displacement of the CoG and the local deformation of the prostate was evaluated using multiple regression analysis.
  
  
  RESULTS
  The mean value and standard deviation (SD) of the prostate deformation were 0.6 mm and 1.7 mm, respectively. For the majority of the patients, the local SD of the deformation was slightly lager in the superior and inferior segments. Multiple regression analysis revealed that the anterior-posterior displacement of the CoG of the prostate had a highly significant correlation with the deformations in the middle-anterior (p < 0.01) and middle-posterior (p < 0.01) segments of the prostate surface (R2 = 0.84). However, there was no significant correlation between the displacement of the CoG and the deformation of the prostate surface in other segments.
  
  
  CONCLUSIONS
  Anterior-posterior displacement of the CoG of the prostate is highly correlated with deformation in its middle-anterior and posterior segments. In the radiation therapy for prostate cancer, it is necessary to optimize the internal margin for every position of the prostate measured using image-guided radiation therapy.
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan; Department of Radiology, Kushiro City General Hospital, Kushiro, Hokkaido, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Nakazawa
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan; Preparatory Office for Proton Therapy Center, Radiation Therapy Research Institute, Social Medical Corporation Teishinkai, Sapporo, Hokkaido, Japan.
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Tateoka
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Saito
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan.
authors.forename: Tadanori
authors.initials: T
authors.lastname: Abe
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Yano
authors.affiliation: Department of Radiology, Kushiro City General Hospital, Kushiro, Hokkaido, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Yaegashi
authors.affiliation: Department of Radiology, Kushiro City General Hospital, Kushiro, Hokkaido, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Narimatsu
authors.affiliation: Preparatory Office for Proton Therapy Center, Radiation Therapy Research Institute, Social Medical Corporation Teishinkai, Sapporo, Hokkaido, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Fujimoto
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Nakata
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan.
authors.forename: Kensei
authors.initials: K
authors.lastname: Nakata
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Someya
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Hori
authors.affiliation: Preparatory Office for Proton Therapy Center, Radiation Therapy Research Institute, Social Medical Corporation Teishinkai, Sapporo, Hokkaido, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Hareyama
authors.affiliation: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Sakata
mesh_terms: D006801:Humans; D008297:Male; D009929:Organ Size; D011467:Prostate / Q000000981:diagnostic imaging* / Q000473:pathology; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011857:Radiographic Image Interpretation, Computer-Assisted