Fifty-eighth annual meeting of the american association of physicists in medicine
SU-F-J-05: The Effect of Air Pockets in the Urinary Bladder During Bladder Hyperthermia Treatment
Hyperthermia combined with Mitomycin C is used for the treatment of non-muscle invasive bladder cancer (NMIBC), using a phased array system of microwave antennas for bladder heating. Often some air is present in the bladder, which effectively blocks the microwave radiation, potentially preventing proper treatment of that part of the bladder. Air can be a relevant fraction of the bladder content and large air pockets are expected to have a noticeable influence on achieved temperatures.
We analysed 14 NMIBC patients treated at our institute with our AMC-4 hyperthermia device with four 70MHz antennas around the pelvis. A CT scan was made after treatment and a physician delineated the bladder on the CT scan. On the same scan, the amount of air present in the bladder was delineated. Using our in-house developed hyperthermia treatment planning system, we simulated the treatment using the clinically applied device settings. We did this once with the air pocket delineated on the CT scan, and once with the same volume filled with bladder tissue.
The patients had on average 4.2ml (range 0.8–10.1ml) air in the bladder. The bladder volume was delineated by the physician, that is including air pocket and bladder wall, was on average 253ml (range 93–452ml). The average volume in which changes exceeded 0.25°C was 22ml (range 0–108 ml), with the bladder being up to 2°C cooler when an air pocket was present. Except for extreme cases, there was no evident relation between the quantity of air and the difference in temperature.
The effect of an air pocket in the bladder during bladder hyperthermia treatment varies strongly between patients. Generally, this leads to lower temperatures in the bladder, potentially affecting treatment quality, and suggesting that care need be taken to minimise the size of air pockets during hyperthermia treatments.
The KWF Dutch Cancer Society financially supported this work, grant UVA 2012-5539.