title: Results of a dummy run of postimplant dosimetry between multi-institutional centers in prostate brachytherapy with 125I seeds.
abstract: OBJECTIVE
  To determine the reproducibility and precision of postimplant dosimetry following (125)I prostate brachytherapy (PB) and to evaluate the effects of learning and experience in CT-based postimplant dosimetry.
  
  
  METHODS
  One-month postimplant CT data from two patients who underwent PB alone or combined therapy (PB + EBRT) were sent to 28 institutions for postimplant dosimetry and analyzed in 2006 (study 1). Similarly, 1-month postimplant CT data from two other patients were also analyzed in 2008 (study 2; 23 institutions). For both modalities in studies 1 and 2, the variance of the difference between CT-based D90 at each institution and CT/MRI fusion-based D90 was estimated.
  
  
  RESULTS
  In monotherapy, F test and Mann-Whitney U test revealed no significant difference in the variance in studies 1 and 2 (P = 0.72, 0.46). In combined therapy, the variance significantly converged in study 2 compared with study 1 (P < 0.05). Even in the two studies, however, the difference between the median CT-based D90 and fusion-based D90 was at least 20-30 Gy.
  
  
  CONCLUSIONS
  Marked interobserver variability was seen in the prostate volume and D90 with CT alone. The precision of postimplant dosimetry based on CT alone was revealed to be limited.
authors.affiliation: Department of Radiology, Jikei University School of Medicine, Tokyo, Japan. maoki@jikei.ac.jp
authors.forename: Manabu
authors.initials: M
authors.lastname: Aoki
authors.forename: Atsunori
authors.initials: A
authors.lastname: Yorozu
authors.forename: Takushi
authors.initials: T
authors.lastname: Dokiya
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008348:Manikins; D015588:Observer Variation; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000379:methods; D015203:Reproducibility of Results; D018709:Statistics, Nonparametric; D014041:Tokyo; D014057:Tomography, X-Ray Computed
chemical_list: D007457:Iodine Radioisotopes