title: Three-dimensional summation of rectal doses in brachytherapy combined with external beam radiotherapy for prostate cancer.
abstract: OBJECTIVE
  To determine the dose constraints for rectal bleeding in brachytherapy (BRT) combined with external beam radiotherapy (EBRT).
  
  
  METHODS
  Post-BRT, pelvic computed tomography images were used for subsequent EBRT planning and BRT postplans in 37 patients. The physical doses for each plan were converted to biologically effective doses, and corresponding voxel doses were integrated to plot the summed dose-volume histogram (sum-DVH). Between 5 patients with (bled-pts) and 32 without (spared-pts) grade 2 or 3 rectal bleeding, the differences in the mean minimal dose (rDn) covering the rectal volume of 0.5-10.0 cc and the rectal volume (rVn) receiving the calculated dose of 20-150Gy were compared.
  
  
  RESULTS
  The differences in the summed-rDn were determined by BRT exposure, while those of the summed-rVn were determined in the low-dose range and superimposed in the high-dose range by EBRT exposure. Of the 13 patients with rV150 of >1.2 cc, 4 were bled-pts (30.8%). Of the 24 patients with rV150 of ≤ 1.2cc, 1 was a bled-pts (4.2%) (p=0.024; odds ratio, 10.2; CI (95%), 1.0-104.3).
  
  
  CONCLUSIONS
  The mono-scale DVH analysis is a promising method for exploring the threshold for rectal bleeding in combined radiotherapy.
authors.affiliation: Department of Radiology, Iwate Medical University School of Medicine, 19-1 Uchimaru, Morioka, Japan. kikuchi@iwate-med.ac.jp
authors.forename: Koyo
authors.initials: K
authors.lastname: Kikuchi
authors.forename: Ryuji
authors.initials: R
authors.lastname: Nakamura
authors.forename: Susumu
authors.initials: S
authors.lastname: Tanji
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Hisao
authors.initials: H
authors.lastname: Kakuhara
authors.forename: Tomonori
authors.initials: T
authors.lastname: Yabuuchi
authors.forename: Wakako
authors.initials: W
authors.lastname: Inatsu
authors.forename: Hirobumi
authors.initials: H
authors.lastname: Oikawa
authors.forename: Hisanori
authors.initials: H
authors.lastname: Ariga
mesh_terms: D000328:Adult; D000368:Aged; D001918:Brachytherapy; D006471:Gastrointestinal Hemorrhage / Q000209:etiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000528:radiation effects*