title: Narrow safety range of intraoperative rectal irradiation exposure volume for avoiding bleeding after seed implant brachytherapy.
abstract: OBJECTIVE
  Rectal toxicity is less common after 125I seed implant brachytherapy for prostate cancer, and intraoperative rectal dose-volume constraints (the constraint) is still undetermined in pioneering studies. As our constraint failed to prevent grade 2 or 3 rectal bleeding (bled-pts) in 5.1% of patients, we retrospectively explored another constraint for the prevention of rectal bleeding.
  
  
  METHODS
  The study population consisted of 197 patients treated with the brachytherapy as monotherapy using real-time intraoperative transrectal ultrasound (US)-guided treatment at a prescribed dose of 145 Gy. Post-implant dosimetry was performed on Day 1 and Day 30 after implantation using computed tomography (CT) imaging. Rectal bleeding toxicity was classified by CTC-AE ver. 3.0 during a mean 29-month (range, 12-48 months) period after implantation. The differences in rV100s were compared among intraoperative, Day 1 and Day 30 dosimetry, and between that of patients with grade 2 or 3 rectal bleeding (the bled-pts) and of the others (the spared-pts). All patients were divided into groups based on provisional rV100s that were increased stepwise in 0.1-cc increments from 0 to 1.0 cc. The difference in the ratios of the bled-pts to the spared-pts was tested by chi-square tests, and their odds ratios were calculated (bled-OR). All statistical analyses were performed by t-tests.
  
  
  RESULTS
  The mean values of rV100us, rV100CT_1, and rV100CT_30 were 0.31 ± 0.43, 0.22 ± 0.36, and 0.59 ± 0.68 cc, respectively. These values temporarily decreased (p = 0.020) on Day 1 and increased (p = 0.000) on Day 30. There was no significant difference in rV100s between the bled-pts and spared-pts at any time of dosimetry. The maximum bled-OR was identified among patients with an rV100us value above 0.1 cc (p = 0.025; OR = 7.8; 95% CI, 1.4-145.8); an rV100CT_1 value above 0.3 cc (p = 0.014; OR = 16.2; 95% CI, 3.9-110.7), and an rV100CT_30 value above 0.5 cc (p = 0.019; OR = 6.3; 95% CI, 1.5-42.3).
  
  
  CONCLUSIONS
  By retrospective analysis exploring rV100 as intraoperative rectal dose-volume thresholds in 125I seed implant brachytherapy for prostate cancer, it is proved that rV100 should be less than 0.1 cc for preventing rectal bleeding.
authors.affiliation: Iwate Medical University PET-Liniac Advanced Medical Center, Uchimaru 19-1, Morioka 020-8505, Japan. rnakamur@iwate-med.ac.jp
authors.forename: Ryuji
authors.initials: R
authors.lastname: Nakamura
authors.forename: Koyo
authors.initials: K
authors.lastname: Kikuchi
authors.forename: Susumu
authors.initials: S
authors.lastname: Tanji
authors.forename: Tomonori
authors.initials: T
authors.lastname: Yabuuchi
authors.forename: Ikuko
authors.initials: I
authors.lastname: Uwano
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Hisanori
authors.initials: H
authors.lastname: Ariga
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Fujioka
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001918:Brachytherapy; D006470:Hemorrhage / Q000209:etiology / Q000517:prevention & control*; D006801:Humans; D007432:Intraoperative Period; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control*; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
chemical_list: D007457:Iodine Radioisotopes