Terminology

Preprocedure

Post Procedure

Outcomes

Procedure

Definitions

• Ablation: Direct application of chemical or thermal therapies to tumors for tissue destruction
• Overall survival (OS): Length of time from either date of diagnosis or start of treatment for disease, such as cancer, to date of death of any cause
  • Usually expressed in median ± standard deviation
• Cancer-specific survival (CSS): Length of time from either date of diagnosis or start of treatment for disease, such as cancer, to date of death from disease
  • Patients who die from causes unrelated to disease are not counted in this measurement
• Progression-free survival: Length of time (from set point, usually treatment) that patient demonstrates no disease progression
• Time to progression: Length of time (from set point, usually treatment) until patient shows disease progression
  • Mortalities are excluded
• Disease-free survival (DFS): Length of time after treatment, until patient dies or shows evidence for recurrent disease

Ablation Modalities

• Radiofrequency ablation (RFA)
  • Physics
    • Relies on electrical conduction through tissue for heat generation
    • Closed circuit necessary for conduction; body acts as resistor
    • Direct radiofrequency heating
      • Occurs within millimeters of applicator needle
    • Thermal conduction
      • Heat transfer more distally; therefore, good thermal conductivity crucial for large ablation
      • Quick charring (dehydration) of tissue increases resistance, opens circuit, and limits ablation zone
      • Slow, gradual "cooking" more effective than fast ablation
    • Common current frequency of 400-500 kHz
  • Disadvantages
    • Irregular ablation shape, depends on thermal conductivity of tissue
    • Charring limits effectiveness
    • Heat sink effect
      • Flow of blood in nearby vessels cools tissue, limiting effectiveness
    • Impedance (instead of temperature) regulating systems may lengthen total procedure time and increase ablation zone
    • Grounding pads required for monopolar systems
    • May require slow and lengthy treatment to effectively kill tumor
• Microwave ablation (MWA)
  • Physics
    • Relies on dielectric heating
      • Alternating electromagnetic (EM) field applied to imperfect dielectric material (tissue); forces water molecules in tissue to oscillate
      • Water molecules oscillate out of phase with EM field
      • Frictional energy loss generates heat
      • Higher water content = better heat absorption and conductivity = larger ablation zone
    • Frequencies often 915 MHz or 2.45 GHz
    • Relative permittivity: How well materials accept EM field (capacitance)
      • Lower the permittivity, the less movement of energy from source dispersed through tissues
      • Low relative permittivity: Bone, spleen
      • High relative permittivity: Muscle, lung, liver
    • Effective conductivity: How well tissue absorbs microwave energy
      • Lower the conductivity, the higher thermal energy deposited locally, and the more effective ablation around antennae
      • Low conductivity: Bone, lung, liver
      • High conductivity: Muscle, blood, spleen
  • Advantages
    • Ablation volume is more predictable, as it does not depend on thermal conductivity of tissue
    • Can pass through and heat tissue at any temperature or water content
    • Less susceptible to heat sink by producing larger areas of active heating
    • Does not require grounding pads
• Cryoablation
  • Physics
    • Relies on Joules-Thomson effect
      • Compressed gas circulates within double-barreled probe
      • Gas released within probe results in sudden pressure drop
      • Resultant temperature drop cools surrounding tissues
    • Process consists of alternate freezing and thawing of tissue (commonly 10 minutes, 8 minutes, 10 minutes)
    • Multifaceted cellular death mode: Cell membrane fracture, apoptosis, vessel thrombosis/ischemia
    • Argon gas
    • Each probe has characteristic isotherms (size and shape of surface with same temperature)
    • Temperatures drop to ~ -150°C at probe
    • Heat pump effect: Nearby vessels may increase temperature and limit ablation margin
  • Advantages
    • Well tolerated (minimal pain)
    • "Ice ball" readily visible with CT (US/MR) guidance
      • Represents 0°C isotherm (not lethal)
      • Lethal isotherm (-20°C) ~ 5 mm inside visible "ice ball"
    • Operator can sculpt irregularly shaped ablation zone by altering orientation of multiple probes
  • Disadvantages
    • More expensive, as multiple probes may be required
    • System requires gas availability and storage

Indications

Contraindications

Preprocedure Imaging

Getting Started

Patient Position/Location

Baseline Imaging and Planning

Probe Insertion/Positioning

Added Maneuvers

Intraprocedural Monitoring of Patient and Treatment

Completion Imaging

Recovery

Things to Do

Complications