Chapter 12
Therapeutic Heating Applications
of Radio Frequency Energy
C-K. Chou
Applications Heating Using RF
• 1. Relieving pain from strains and sprains
• 2. Increasing blood flow
• 3. Combining hyperthermia (42-45o C) with
radiation treatment of cancers.
• 4. Radio Frequency Ablations of tumors.
(50 to 100o C)
Major Issues
• 1. Measurement and control of the
temperature distributions.
• 2. RF is hard to localize to the desired region
because of long wave length
• 3. Differential heating of tissue types
•
fat , bone vs muscles, liver etc.
• 4. Blood flow cooling is both a positive and
negative.
Mechanism of Heating
• 1. Resistive heating σE2
• 2. Dielectric heating ε’’ or σ=ωεo ε”
Typical Heating Pattern at 50W
Limits
• 1. Need to get to high enough temperature
42-44o C but not so high as to carbonize
the tissue.
• 2. Need to stay hot for long enough to effect
the cancer but not so long as to raise the
temperature of the normal tissue to
damaging levels. (≈45o C)
• 3. For ablation you want ΔT= 15 to 60o C for a
short time < 6min
Cancer Treatment
• 1. Hyperthermia alone not very effective.
• 2. Hyperthermia plus Radiation Treatment
better.
• 3. The synergism of RT and HT is the thermal
killing of hypoxic and S phase DNA
syntheses cell that are resistive to
radiation alone.
• 4. The heating can also increase the
effectiveness of the chemotherapy drugs.
Problems
• 1. It is hard to get the heating just where you
want it.
• 2. It is hard to control the temperature to the
very narrow range you need.
• 3. The equipment is expensive.
RF Hyperthermia Plus MRI
Clinical Trials As of 2006
• 1. Some success
– A breast cancer trial
– HT + RT compared to RT alone 59% vs 41%
– Head and Neck Cancer trail
– HT +RT 58% vs 20%
.2 Superficial Malignancies HT +RT 32% vs 30%
3. Malignant Melanoma RT followed by HT 46% vs
28%
RF Ablation or RFA
• 1. Use for correcting cardiac Arrhythmias
• 2. Heat source for inducing coagulation
necrosis in tumors.
• 3, Heat to 50o C or more However less than
100o C. Higher temperatures lead to faster
results
• 4. You want to maintain this temperature over
the entire target volume for 4 =6 minutes
Exposures
• 1. Typical 10 to 30min.
• 2. For a single electrode coagulated volume
less than 1.6cm diameter.
• 3. Larger volumes with multiple electrodes
Results
• 1. On over 3000 RFA treated patients with
small percutaneous (<3cm) liver tumors.
• 2 Complete Local Response averaged 70-75%
for 3-5 cm tumors but only 25% for larger
tumors.
• 3. 40-50% survival rates at 5 years.
• 4. Other tumors similar results.