title: Local Hypothermia as a Radioprotector of the Rectal Wall During Prostate Stereotactic Body Radiation Therapy.
abstract: To compare the single-fraction dose-related incidence of rectal obstruction and/or bleeding in normothermic and hypothermic rectums of a rat model.
  
  
  
  A 1.9-cm length of rectum was irradiated with a single fraction in 57 Sprague-Dawley rats using a dedicated image-guided small animal irradiator and Monte Carlo-based treatment planning system. All rats had a rectal temperature control apparatus placed during irradiation and were stratified to achieve either a normothermic (37°C) or hypothermic (15°C) rectal wall temperature. Radiation was delivered to a 1-cm-diameter cylindrical volume about the cooling device and rectal wall. The radiation dose was escalated from 16 Gy up to 37 Gy to assess the dose response in each arm. The primary endpoint of this study was rectal obstruction and/or bleeding during a follow-up of 180 to 186 days. Histologic scoring was performed on all study rats.
  
  
  
  Probit analysis showed a dose associated with a 50% incidence of rectal obstruction of 24.6 Gy and 40.8 Gy for normothermic and hypothermic arms, respectively. The occurrence of obstruction and/or bleeding correlated with the posttreatment histologic score for normothermic rats; however, there was no difference in histologic score between normothermic and hypothermic rats at the highest dose levels evaluated.
  
  
  
  A significant radioprotective effect was observed using local hypothermia during a single large dose of radiation for the functional endpoint of rectal obstruction and/or bleeding. A confirmatory study in a large animal model with anatomic and physiologic similarities to humans is suggested.
authors.affiliation: Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, Texas. Electronic address: Brian.Hrycushko@utsouthwestern.edu.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hrycushko
authors.affiliation: Department of Radiology, UT Southwestern Medical Center, Dallas, Texas.
authors.forename: Rajiv
authors.initials: R
authors.lastname: Chopra
authors.affiliation: Department of Biostatistics, University of California, Los Angeles, Los Angeles, California; Department of Radiology, University of California, Los Angeles, Los Angeles, California.
authors.forename: James W
authors.initials: JW
authors.lastname: Sayre
authors.affiliation: Department of Pathology, UT Southwestern Medical Center, Dallas, Texas; Department of Molecular Biology, UT Southwestern Medical Center, Dallas, Texas.
authors.forename: James A
authors.initials: JA
authors.lastname: Richardson
authors.affiliation: Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, Texas.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Folkert
authors.affiliation: Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, Texas.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Timmerman
authors.affiliation: Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, Texas.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Medin
mesh_terms: D000818:Animals; D001831:Body Temperature; D005260:Female; D006471:Gastrointestinal Hemorrhage / Q000209:etiology; D007036:Hypothermia, Induced / Q000379:methods*; D007415:Intestinal Obstruction / Q000209:etiology; D008297:Male; D009010:Monte Carlo Method; D059351:Organ Sparing Treatments / Q000379:methods*; D011829:Radiation Dosage; D011833:Radiation Injuries, Experimental / Q000517:prevention & control*; D011835:Radiation Protection / Q000379:methods*; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012002:Rectal Diseases / Q000209:etiology; D012007:Rectum / Q000528:radiation effects*