title: Interfractional fluctuation of rectal dose in high dose rate brachytherapy for prostate cancer.
abstract: OBJECTIVE
  The aim of the study was to explore the cause of the difference in the maximal rectal dose between the first and second high dose rate (HDR) brachytherapy applications by comparing the thickness of the anterior rectal wall.
  
  
  METHODS
  The rectal dose and the thickness of the anterior rectal wall were analyzed in 26 patients with prostate cancer. After undergoing external beam radiation treatment with a total isocenter dose of 50 Gy, they were treated with HDR brachytherapy of 7.5 Gy/fraction, two fractions daily. The interval between the first HDR brachytherapy session and the second was 5 h. The rectal doses were directly surveyed during irradiation of the HDR brachytherapy. Thickening of the anterior rectal wall was measured at the same level by axial computed tomography scans obtained before the first and second HDR brachytherapy applications.
  
  
  RESULTS
  The maximal surveyed rectal doses during the first and second HDR brachytherapy applications were 188 +/- 51 cGy and 220 +/- 35 cGy, respectively (P < 0.01). The fluctuation ratio exceeded 1 in each case. The thickness of the anterior rectal wall before the first and second HDR brachytherapy applications was 18.78 +/- 4.34 mm and 14.95 +/- 4.09 mm (P < 0.01), respectively. The fluctuation difference exceeded 0 in each case.
  
  
  CONCLUSIONS
  The different rectal dose is attributable to thinning of the anterior rectal wall. The total rectal dose is within the range of doses at risk of exerting a toxic effect on the rectum.
authors.affiliation: Department of Radiation Oncology, Wakayama Medical University, 811-1 Kimiidera, Wakayama, 641-0012, Japan.
authors.forename: Hime
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Morio
authors.initials: M
authors.lastname: Sato
authors.forename: Shintaro
authors.initials: S
authors.lastname: Shirai
authors.forename: Kazushi
authors.initials: K
authors.lastname: Kishi
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Naya
authors.forename: Hisaki
authors.initials: H
authors.lastname: Tokunaga
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001918:Brachytherapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation; D012007:Rectum / Q000033:anatomy & histology / Q000528:radiation effects*