title: Timing of postseed imaging influences rectal dose-volume parameters for cesium-131 prostate seed implants.
abstract: OBJECTIVE
  To study the influence of timing of postseed implant imaging on rectal dose-volume parameters for cesium-131 ((131)Cs) seed prostate implants.
  
  
  METHODS
  Fifteen patients were treated in our institution with combination (131)Cs brachytherapy followed by pelvic external beam radiation therapy for intermediate to high-risk prostate cancers. For all patients, CT scans were scheduled at 7 days (CT(7)) and again at 2 months for external beam radiation therapy simulation purpose (CT(60)) postseed implantation. Comprehensive postseed implant dosimetry was performed for both CT(7) and CT(60) scans. In each case, dose-volume histogram parameters, rectal separation (the distance between the center of posterior most seed and most anterior rectal wall), and posterior row activity (the total activity implanted within 2-4mm anterior to the posterior wall of the prostate) data were collected. The absolute rectal volumes receiving 100% and 110% prescription dose were also collected.
  
  
  RESULTS
  Rectal dose correlated strongly with rectal separation (p<0.001). The mean change in rectal separation between CT(7) and CT(60) scans was 1.1 (±1.7) mm, and the corresponding change in 0.1-cc rectal dose was 18 (±26.5) Gy. Posterior row activity did not correlate with rectal dose (p=0.51). The mean volume of rectum that receives between 100% and 110% of the prescription dose (RV(100) and RV(110)) increased twofold, between CT(7) and CT(60) evaluations (0.03 [±0.06] cc vs. 0.07 (±0.05) cc, respectively, p=0.06).
  
  
  CONCLUSIONS
  Our study has demonstrated that rectal doses after (131)Cs seed implants are influenced by the timing of postseed imaging. This may be a consequence of prostatic and periprostatic edema resolution.
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, NY 10467, USA. ryaparpa@montefiore.org
authors.forename: Ravindra
authors.initials: R
authors.lastname: Yaparpalvi
authors.forename: Raquibul
authors.initials: R
authors.lastname: Hannan
authors.forename: Evan
authors.initials: E
authors.lastname: Landau
authors.forename: Norman
authors.initials: N
authors.lastname: Kahan
authors.forename: William
authors.initials: W
authors.lastname: Bodner
authors.forename: Hsiang-Chi
authors.initials: HC
authors.lastname: Kuo
authors.forename: Lloyd
authors.initials: L
authors.lastname: Minsky
authors.forename: Keyur J
authors.initials: KJ
authors.lastname: Mehta
authors.forename: Madhur K
authors.initials: MK
authors.lastname: Garg
authors.forename: Shalom
authors.initials: S
authors.lastname: Kalnicki
authors.forename: Chandan
authors.initials: C
authors.lastname: Guha
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001918:Brachytherapy / Q000295:instrumentation*; D002586:Cesium; D006801:Humans; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011874:Radiometry; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects*; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D002586:Cesium