title: Modeling Cryotherapy Ice Ball Dimensions and Isotherms in a Novel Gel-based Model to Determine Optimal Cryo-needle Configurations and Settings for Potential Use in Clinical Practice.
abstract: To gain a better understanding of ice ball dimensions and temperature isotherms relevant for cell kill when using combinations of cryo-needles we set out to answer 4 questions: (1) what type of cryo-needle? (2) how many needles? (3) best spatial configuration? and (4) correct duty cycle percentage?
  
  
  
  We conducted laboratory experiments to monitor ice ball dimensions and create multi-needle planar isotherm maps for 17G and 10G cryo-needles using a novel multi-needle thermocouple fixture within gel at body temperature. We tested configurations of 1-4 cryo-needles at duty cycles of 20%-100% with 1-2.5 cm spacing.
  
  
  
  Analysis of various combinations shows that a central core of ≤-40°C develops at a distance of ~1 cm around the cryo-needles. Temperature increases linearly from this point to the ice ball leading edge (0°C), which is a further ≈1 cm away. Thus, the -40°C isotherm is approximately 1 cm inside the leading edge of the ice ball. The optimum distance between cryo-needles was 1.5-2 cm, at duty cycle settings of 70%-100%. At distances further apart or with lower duty cycle settings, ice balls either had a central core >-40°C or had an hourglass shape.
  
  
  
  In answer to questions 1-3, tumor length, diameter, and shape will ultimately determine the number of needles and their configuration. However, we propose a conservative distance for cryo-needle placement between 1 and 1.5 cm should be adopted for clinical practice. In answer to question 4, using low duty cycle settings runs the risk of incomplete -40°C isotherm coverage of the tumor, and thus in routine practice we suggest that settings of 70%-100% are most appropriate.
authors.affiliation: Division of Surgery and Interventional Science, University College London, London, UK; Department of Urology, University College London Hospitals NHS Foundation Trust, London, UK; Whittington Hospital, London, UK. Electronic address: taimur.shah@ucl.ac.uk.
authors.forename: Taimur T
authors.initials: TT
authors.lastname: Shah
authors.affiliation: Galil Medical Ltd., Yokneam, Israel.
authors.forename: Uri
authors.initials: U
authors.lastname: Arbel
authors.affiliation: Galil Medical Inc., Arden Hills, MN.
authors.forename: Sonja
authors.initials: S
authors.lastname: Foss
authors.affiliation: Galil Medical Inc., Arden Hills, MN.
authors.forename: Andrew
authors.initials: A
authors.lastname: Zachman
authors.affiliation: Division of Surgery and Interventional Science, University College London, London, UK; Department of Urology, University College London Hospitals NHS Foundation Trust, London, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Rodney
authors.affiliation: Division of Surgery and Interventional Science, University College London, London, UK; Department of Urology, University College London Hospitals NHS Foundation Trust, London, UK.
authors.forename: Hashim U
authors.initials: HU
authors.lastname: Ahmed
authors.affiliation: Division of Surgery and Interventional Science, University College London, London, UK; Department of Urology, University College London Hospitals NHS Foundation Trust, London, UK; Princess Alexandra Hospital NHS Trust, Harlow, UK.
authors.forename: Manit
authors.initials: M
authors.lastname: Arya
mesh_terms: D003452:Cryosurgery / Q000295:instrumentation*; D005782:Gels; D007053:Ice; D008961:Models, Structural; D009339:Needles; D013696:Temperature
chemical_list: D005782:Gels; D007053:Ice