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 (42-45 o C) with radiation treatment of cancers. 4. Radio Frequency Ablations of tumors. (50 to 100 o 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 σE 2 2. Dielectric heating ε’’ or σ=ωε o ε”

Typical Heating Pattern at 50W

Limits 1. Need to get to high enough temperature o 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. (≈45 o C) 3. For ablation you want ΔT= 15 to 60 o 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 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 50 o C or more However less than 100 o 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 % survival rates at 5 years. 4. Other tumors similar results.