WHAT IS RADIOFREQUENCY ABLATION
AND HOW DOES IT DESTROY TUMOURS?

RFA's mechanism is elegant in its simplicity. Understanding it removes the mystery of how a needle can permanently destroy a tumour.

“RFA is not a new idea — surgeons have used electrical current to cut and coagulate tissue for over a century. RFA takes the same principle and applies it precisely inside a tumour, using imaging guidance to place the electrode exactly where it needs to be.”

• Step 1: Alternating Electrical Current

  A radiofrequency generator (typically 375–500 kHz) passes high-frequency alternating current through the electrode needle. This is the same electromagnetic frequency range as AM radio — hence the name. The frequency is too high to cause muscle or nerve stimulation (which lower frequencies would cause), making the current safe to pass through living tissue.

• Step 2: Resistive Heating in Tissue

  As the alternating current flows from the electrode tip into the surrounding tissue and then to grounding pads on the patient's legs or back, the tissue resists the current flow. This resistance converts electrical energy to heat — in the same way a wire heats up when current passes through it. Heat generation is concentrated around the electrode tip where current density is highest.

• Step 3: Coagulative Necrosis at 60°C+

  Cell death begins at approximately 50°C and is instantaneous and irreversible above 60°C — due to protein denaturation in cell membranes and enzymes. The target temperature at the tumour is 60–100°C. Temperatures above 100°C cause charring and steam formation, which actually reduces electrical conductivity and limits further heat spread — a self-limiting ceiling.

• Step 4: The Ablation Zone

  The region of tissue heated above 60°C forms a zone of complete coagulative necrosis — typically an ovoid or spherical volume 2–5 cm in diameter per electrode position, depending on the RFA system and energy settings. The goal is a zone that covers the entire tumour plus at least a 0.5–1 cm margin of adjacent tissue to ensure complete tumour destruction.

Different electrode designs achieve different ablation zone sizes and shapes. The interventional radiologist selects the electrode type based on tumour size and location.

• Single Straight Electrode (Monopolar)

  The simplest design — a single insulated needle with an exposed active tip. Current flows from the electrode tip through the patient to grounding pads. Ablation zone is a sphere or ellipsoid around the tip. Single electrodes typically create ablation zones of 2–3 cm per position. For tumours larger than 3 cm, the electrode is repositioned multiple times ("multiple overlapping ablations") or a multi-tined design is used.

• Expandable Multi-Tined Electrodes

  A retractable electrode that deploys multiple curved tines (hooks) from the needle shaft once positioned inside the tumour — like an umbrella opening. Tines spread through the tumour over a 3–5 cm diameter. The umbrella configuration increases ablation zone size in a single deployment, reducing the number of electrode positions needed for larger tumours. Examples: RITA/AngioDynamics starburst, Boston Scientific LeVeen systems.

• Internally Cooled Electrodes

  Chilled saline is circulated through the electrode shaft during energy delivery, cooling the electrode tip. This prevents charring at the electrode surface (which would reduce conductivity), allowing higher power delivery and larger ablation zones — typically 3–4 cm per position. Internally cooled single or cluster electrodes are the current standard in most centres. Examples: Medtronic (formerly Covidien) Cool-tip system.

• Bipolar Electrodes

  Current flows between two electrodes placed within the tumour rather than through the patient to grounding pads. This localises energy delivery more precisely and eliminates the risk of current concentration at grounding pad sites. Bipolar RFA is less common than monopolar but offers advantages in selected locations. Some newer systems use multipolar approaches with 3+ electrodes simultaneously.

How RFA compares to microwave ablation (MWA), cryoablation, and irreversible electroporation (IRE) — all interventional oncology tools with distinct strengths.

Precise electrode placement is everything in RFA. The margin of success or failure is measured in millimetres. Three imaging modalities guide electrode placement.

• CT Guidance

  The standard for most liver, lung, and kidney RFA. The patient lies in the CT scanner; intermittent CT acquisitions track the needle as it advances through skin and tissue toward the tumour. CT provides excellent anatomical detail in three planes, allows precise depth measurement, and confirms final electrode position. CT-fluoroscopy enables real-time needle guidance in experienced hands.

• Ultrasound Guidance

  Used for superficial liver tumours and kidney tumours clearly visible on ultrasound. Allows real-time needle visualisation during placement and during energy delivery — the treating radiologist can monitor the ablation zone as it develops (appearing as an echogenic bubble on ultrasound). Faster and involves no radiation. Less useful for tumours poorly visualised on ultrasound or deep liver locations.

• MRI Guidance

  Less common but offers superior soft tissue contrast and the ability to thermally map the ablation zone in real time using MR thermometry. Specialised MR-compatible RFA systems are required. Used for selected cases where CT or ultrasound is inadequate — particularly prostate RFA and selected liver cases.

The heat sink effect is the single most important factor limiting RFA success — and the primary reason microwave ablation was developed as an improvement over RFA.

• What the Heat Sink Effect Is

  Blood flowing through vessels adjacent to a tumour carries heat away from the ablation zone — just as a heat sink in electronics dissipates heat. The continuous flow of blood at 37°C in a major vessel (hepatic vein, portal vein branch, renal vein) adjacent to the tumour keeps the near-vessel tissue cooler than the target temperature, preventing complete tumour destruction in that area.

• Clinical Consequences

  Perivascular tumours — those within 0.5–1 cm of a major vessel — have significantly higher incomplete ablation and local recurrence rates with RFA than tumours located away from vessels. A tumour touching a hepatic vein may achieve complete ablation in 60–70% of cases vs 90%+ for tumours distant from vessels. This is the primary reason microwave ablation (which generates much higher temperatures that overcome heat sink) is preferred for perivascular liver tumours.

Learn more about specific RFA indications and evidence.

Frequently Asked Questions

Common questions about what RFA is and how it works.