title: Changes of dose delivery distribution within the first month after permanent interstitial brachytherapy for prostate cancer.
abstract: OBJECTIVE
  To evaluate changes of dose distribution for both the prostate and the surrounding tissues after permanent brachytherapy as monotherapy for prostate cancer.
  
  
  METHODS
  In 35 patients, CT scans were performed before, 1 day after (day 1) and 1 month after the implantation (day 30). Changes of prostate volume, dosimetric parameters, and distances between posterior prostate contour and rectal wall as well as prostate contour and prescription isodose were analyzed.
  
  
  RESULTS
  Prostate volume increased from 37+/-11 cm3 (mean+/-standard deviation) to 49+/-12 cm3 on day 1 and dropped to 40+/-9 cm3 on day 30. Prostate V100 increased from 87+/-7% to 90+/-7%, prostate D90 from 138+/-21 Gy to 151+/-30 Gy. Mean rectal volume covered by the prescription isodose rose from 0.4 cm3 to 1.0 cm3; a changing distance between the prostate and rectal wall was excluded as a reason. Prostate D90 (day 1) and rectum V100 (day 30) proved to be significantly higher for larger prostate sizes. The distance between the prescription isodose and the prostate contour increased particularly at the posterior and inferior borders: 1.9 mm and 2.5 mm on average (0.1 mm and -0.7 mm at opposite borders, respectively).
  
  
  CONCLUSIONS
  With a decreasing edema of the prostate, an increasing dose both to the prostate and the anterior rectal wall resulted--the postimplant interval is essential for the dosimetry report. Due to a larger edema, a higher prescription dose might be needed for optimal cancer control in smaller prostates. Compared to day 1, the dose to the surrounding tissues increased on day 30, particularly at the posterior and inferior prostate borders.
authors.affiliation: Department of Radiotherapy, RWTH Aachen, Aachen, Germany. mpinkawa@ukaachen.de
authors.forename: Michael
authors.initials: M
authors.lastname: Pinkawa
authors.forename: Bernd
authors.initials: B
authors.lastname: Gagel
authors.forename: Marc Dieter
authors.initials: MD
authors.lastname: Piroth
authors.forename: Holger
authors.initials: H
authors.lastname: Borchers
authors.forename: Gerhard
authors.initials: G
authors.lastname: Jakse
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Eble
mesh_terms: D001918:Brachytherapy; D003627:Data Interpretation, Statistical; D004307:Dose-Response Relationship, Radiation; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects; D013997:Time Factors; D014057:Tomography, X-Ray Computed