title: Comparison of depth of necrosis using cryotherapy by gas and number of freeze cycles.
abstract: OBJECTIVE
  This study aimed to establish the noninferiority of a single-freeze application with CO2 or N2O compared with the standard double freeze with N2O for cryotherapy treatment.
  
  
  METHODS
  Sixty women undergoing hysterectomy for reasons other than cervical cancer or precancer were randomized to 1 of 3 techniques as follows: (1) double freeze with N2O, (2) single freeze with N2O, or (3) single freeze with CO2. The cervix was separated and cut into anterior and posterior segments, and the deepest area of necrosis was recorded. Comparisons were made using regression analysis. The margin of noninferiority was defined as 0.8 mm.
  
  
  RESULTS
  On the anterior lip, a single freeze with N2O was noninferior to a double freeze of the same gas, but on the posterior lip, the single freeze was not. The single freeze of CO2 did not provide sufficient depth of necrosis in either lip to infer noninferiority versus the double freeze with N2O.
  
  
  CONCLUSIONS
  A single freeze with N2O is noninferior to a double-freeze technique in the anterior but not the posterior lip. However, the result for posterior lips was close to reaching statistical significance. In addition, CO2 had approximately 1 mm shallower depth of necrosis compared with N2O techniques; however, the clinical implications are unknown. Given the extensive use of CO2 globally, further clinical evaluation is needed.
authors.affiliation: 1University of Pittsburgh Medical Center, Pittsburgh, PA; 2Basic Health International, New York, NY; 3Program for Appropriate Technology in Health (PATH), Seattle, WA; 4Instituto Nacional de Enfermedades Neoplásicas, Lima, Peru; 5Hampshire College, Amherst, MA; 6Department of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville; and 7Global Cancer Initiative, Chestertown, MD; and 8Global Coalition Against Cervical Cancer, Arlington, VA.
authors.forename: Miriam
authors.initials: M
authors.lastname: Cremer
authors.forename: Lauren
authors.initials: L
authors.lastname: Ditzian
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Winkler
authors.forename: José
authors.initials: J
authors.lastname: Jerónimo
authors.forename: Jered
authors.initials: J
authors.lastname: Singleton
authors.forename: Henry Valdivia
authors.initials: HV
authors.lastname: Franco
authors.forename: Mauricio
authors.initials: M
authors.lastname: Maza
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Conlisk
authors.forename: Julia
authors.initials: J
authors.lastname: Gage
authors.forename: Philip
authors.initials: P
authors.lastname: Castle
authors.forename: Carlos
authors.initials: C
authors.lastname: Santos
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000627:therapeutic use; D002584:Cervix Uteri / Q000528:radiation effects*; D017679:Cryotherapy / Q000379:methods*; D005260:Female; D005740:Gases / Q000627:therapeutic use*; D006801:Humans; D008875:Middle Aged; D009336:Necrosis; D009609:Nitrous Oxide / Q000627:therapeutic use
chemical_list: D005740:Gases; D002245:Carbon Dioxide; D009609:Nitrous Oxide