title: Difference in rectal dosimetry between pre-plan and post-implant analysis in transperineal interstitial brachytherapy for prostate cancer.
abstract: OBJECTIVE
  To investigate differences in rectal dosimetry between pre-plan ultrasonography (US) and post-implant computed tomography (CT).
  
  
  METHODS
  Subjects comprised 49 patients who underwent prostate brachytherapy using (125)I seed implants. Prescribed dose was 145Gy to the periphery of the prostate. Differences in rectal dosimetry between pre-plan US and post-implant CT analysis were evaluated. In addition, patients were divided into two groups according to timing of pre-planning (pre-plan group, n=28; intraoperative pre-plan group, n=21), and differences in rectal dosimetry between groups were assessed.
  
  
  RESULTS
  The average of volume differences between pre-plan and post-implant analysis (pre-plan minus post-implant analysis) for all patients were follows: -0.08 cm(3) in V60 (volume of rectal wall receiving 60% of prescribed dose); -0.05 cm(3) in V70; -0.16 cm(3) in V80; -0.38 cm(3) in V90; -0.40 cm(3) in V100; -0.32 cm(3) in V110; -0.22 cm(3) in V120; -0.15 cm(3) in V130; -0.10 cm(3) in V140; -0.07 cm(3) in V150; and -0.05 cm(3) in V160. Apparent differences between pre-plan US and post-implant CT in rectal dosimetry were small. However, considering the steep curve of the relationship between tolerable volume and dose, a large actual difference should be assumed. No advantage was identified for the intraoperative pre-plan group. Safe volume to avoid proctitis tended to be smaller on ultrasonography than on CT at 1 month.
  
  
  CONCLUSIONS
  The present work shows that direct comparison of CT analysis and pre-plan US is unfavorable due to large differences in these modalities and overestimation of tolerable volume. However, by comprehending the degree of difference, comparison of data from CT analysis with a US pre-plan may be feasible and useful for providing feedback between these modalities.
authors.affiliation: Department of Radiology, Kitasato University School of Medicine, Kanagawa, Japan. hishiyam@kitasato-u.ac.jp
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Ishiyama
authors.forename: Masashi
authors.initials: M
authors.lastname: Kitano
authors.forename: Takefumi
authors.initials: T
authors.lastname: Satoh
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Niibe
authors.forename: Mineko
authors.initials: M
authors.lastname: Uemae
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fujita
authors.forename: Shiro
authors.initials: S
authors.lastname: Baba
authors.forename: Kazushige
authors.initials: K
authors.lastname: Hayakawa
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D005500:Follow-Up Studies; D006801:Humans; D007430:Intraoperative Care; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D010502:Perineum; D011349:Proctitis / Q000517:prevention & control; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control; D019275:Radiopharmaceuticals / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D018084:Ultrasonography, Interventional
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals