ESTRO 36 Abstract Book

S950 ESTRO 36 _______________________________________________________________________________________________

present in the bladder during treatment, which effectively blocks the microwave radiation used to warm the bladder. This may lead to a lower thermal dose to the bladder wall, which is associated with a lower treatment response. This study investigates the size of that effect. Material and Methods We analysed thirteen NMIBC patients treated at our institute with mitomycin C (40 mg in 50 ml) plus hyperthermia (60 min). Hyperthermia was delivered using our hyperthermia device with four 70 MHz 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 with the air pocket delineated on the CT scan, and alternatively with the same volume filled with fluid The patients had on average 4.2 ml (range 0.8 – 10.1 ml) air in the bladder. The bladder volume delineated by the physician (including air pocket and bladder wall), was on average 253 ml (range 93 – 452 ml). The average bladder volume in which changes exceeded 0.25 °C was 22 ml (range 0 – 108 ml), with the bladder being up to 2 °C cooler when an air pocket was present. There was no evident relation between the quantity of air and the difference in temperature. Although in particular the part of the bladder close to the air pocket absorbs less energy, the temperature in the entire bladder is typically lower because of convective mixing in the bladder contents. (urine). Results

Conclusion The effect of an air pocket in the bladder during bladder hyperthermia treatment varies strongly between patients, and no relation was visible between effect size and air volume. 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. EP-1730 Opal - The Oncology Portal and Application J. Kildea 1 , L. Hendren 2 , D. Hererra 3 , A. Joseph 4 , R. Maglieri 5 , T. Hijal 6 1 McGill University Health Centre, Medical Physics Unit, Montreal, Canada 2 McGill University, School of Computer Science, Montreal, Canada 3 University of Waterloo, Computer Science Department, Waterloo, Canada 4 McGill University, Medical Physics Unit, Montreal, Canada 5 McGill University Health Centre, Medical Physics, 1001 boul Décarie- Montreal, Canada