title: MRI-CT fusion to assess postbrachytherapy prostate volume and the effects of prolonged edema on dosimetry following transperineal interstitial permanent prostate brachytherapy.
abstract: OBJECTIVE
  Quality assurance through postplan assessment is an integral part of permanent seed prostate implants. The use of MRI-CT fusion for 1-month postimplant dosimetry permits accurate assessment of prostate volume without seed induced artifact and uncertainties of prostate contour inherent to CT assessments. Routine use of MRI-CT fusion reveals significant prostate edema may persist several weeks. This study evaluates the effect of edema, and its subsequent resolution, on dosimetry.
  
  
  METHODS
  From May 2001 to June 2003, 241 men were treated with (125)I seed implants based on a transrectal ultrasound (TRUS) preplan. Quality assessment was performed at 1 month by CT-MRI fusion using VariSeed software. Over this 24-month period, 29 patients (12%) with residual edema at 1 month (12-60% >TRUS plan volume), had repeat CT-MRI fusion at 2-4 months to reassess volume and dosimetry. Eleven of the 29 had received prior androgen ablation to shrink the prostate preimplant.
  
  
  RESULTS
  For the entire group (n = 241), mean preimplant prostate volume was 33.7 cc and median postplan dosimetric parameters were: V100, 92.2%; D90, 153 Gy; and V150, 53%. For the 29 patients with prolonged edema, mean preimplant volume was 34.8 cc and 1-month volume was 46.1 cc (p <0.001). Mean volume reduction between 1 and 2 months was 13%. The decrease in prostate volume had a significant effect on dosimetry with median increase between 1 month and 2 months in calculated V100 of 9.5%, V150 22.6%, V200 30.1%, and D90 11.5%.
  
  
  CONCLUSIONS
  Significant residual edema is seen 1-month postimplant in 12% of prostates and may have a profound effect on dosimetry. Further study is underway to characterize the time course of resolution of the edema, and to perform integral dosimetry based on the changing volume.
authors.affiliation: Department of Radiation Oncology, Princess Margaret Hospital, 610 University Avenue, Toronto, Canada, M5G 2M9. juanita.crook@rmp.uhn.on.ca
authors.forename: Juanita
authors.initials: J
authors.lastname: Crook
authors.forename: Michael
authors.initials: M
authors.lastname: McLean
authors.forename: Ivan
authors.initials: I
authors.lastname: Yeung
authors.forename: Theresa
authors.initials: T
authors.lastname: Williams
authors.forename: Gina
authors.initials: G
authors.lastname: Lockwood
mesh_terms: D001918:Brachytherapy / Q000009:adverse effects* / Q000379:methods; D004487:Edema / Q000209:etiology*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging; D008297:Male; D010043:Outcome and Process Assessment, Health Care; D011467:Prostate / Q000000981:diagnostic imaging* / Q000473:pathology / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000209:etiology*; D014057:Tomography, X-Ray Computed
chemical_list: D007457:Iodine Radioisotopes