title: Correlation between pre- and postimplant dosimetry for iodine-125 seed implants for localized prostate cancer.
abstract: OBJECTIVE
  In order to evaluate implant quality for permanent prostate brachytherapy in patients with localized prostate cancer, American Brachytherapy Society and ESTRO guidelines recommend that postimplant dosimetry should be performed. To understand more about the relationship between pre- and postimplant dosimetry, a comparison was made of patients who received iodine-125 ((125)I) brachytherapy between March 1995 and the end of 2004, using a preplan technique.
  
  
  METHODS
  CT postimplant dosimetry was available for 707 patients. Detailed dose volume analysis was performed using both preimplant ultrasound and postimplant CT data sets for a subgroup of 445 patients. The following parameters were compared: prostate volume covered by 100% of the prescription dose (Vp100), Vp150, and Vp200 and dose to 90% (D90) of the prostate. In addition, volume implanted (Vi) parameters were used to compare pre- and postimplant dosimetry. Vi parameters describe dose levels inside the patient, based on number of seeds, seed activity, and their spatial distribution relative to each other, without reference to the actual prostate volume or position.
  
  
  RESULTS
  The mean +/- standard deviation values of preimplant (34.7 +/- 8.9 cm(3)) and postimplant (36.7 +/- 9.4 cm(3)) prostate volumes were similar. The mean (+/-standard deviation) planned D90 was 183.4 (+/-12.1) Gy while the D90 that was achieved was 145.5 (+/-20.4) Gy. Over the study period, there was a steady increase of the average D90. Postimplant CT D90 and Vp100 values correlated significantly (R = 0.84; p < 0.001). The Vi and Vp parameters all showed a strong correlation.
  
  
  CONCLUSIONS
  In this study, we showed that there is a strong correlation between transrectal ultrasound-based preimplant and CT-based postimplant dosimetry. The excellent correlation between prostate D90 and V100 values demonstrates they are both equally valid quality indices. Vi parameters are an additional measure that can be used to assess the quality of the implant.
authors.affiliation: Department of Medical Physics and Engineering, St James's Institute of Oncology, Leeds LS9 7TF, United Kingdom.
authors.forename: Bashar
authors.initials: B
authors.lastname: Al-Qaisieh
authors.forename: Thelma
authors.initials: T
authors.lastname: Witteveen
authors.forename: Brendan
authors.initials: B
authors.lastname: Carey
authors.forename: Ann
authors.initials: A
authors.lastname: Henry
authors.forename: David
authors.initials: D
authors.lastname: Bottomley
authors.forename: Jonathan
authors.initials: J
authors.lastname: Smith
authors.forename: Kevin
authors.initials: K
authors.lastname: Franks
authors.forename: Peter
authors.initials: P
authors.lastname: Bownes
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden; D014463:Ultrasonography
chemical_list: D007457:Iodine Radioisotopes