Air cooling for an interstitial microwave hyperthermia antenna: theory and experiment

Microwave antennas are inserted through brachytherapy catheters implanted in a tumor to deliver interstitial hyperthermia cancer therapy. Theoretical calculations show that a cooling rate on the order of 0.1 W/cm length of catheter will significantly improve the radial uniformity of the temperature distribution of single antennas or arrays. Experiments and theoretical calculations show that air passing through the annulus between the antenna and the catheter at 10 L/min or less will produce such a cooling rate in a 2.2-mm OD catheter that has both ends accessible. To maintain uniformity of cooling rate along the catheter, it is better to control the cooling rate by preheating the air entering the catheter to 30-40 degrees C than it is to control the flow rate of room-temperature air. Ohmic heating of the antenna feedline does not confound the air cooling action significantly.