On the improvement of regional hyperthermia treatment

Abstract

Hyperthermia is an adjuvant treatment modality to radiotherapy and/or chemotherapy, with the aim of increasing the tumour killing effect of the treatment. It involves the elevation of the tumour temperature to ~ 42oC. Radiofrequent heating is a practical method for hyperthermia: a number of externally positioned antennas radiate waves that penetrate the body and cause a local temperature increase. Frequencies from 70 MHz to 110 MHz are used for regional hyperthermia, that is applied to tumours in the pelvic region, like cervical, bladder, prostate and rectal tumours. During hyperthermia a number of treatment limiting effects occur, like local pain and general discomfort, that limit the total applied power. Due to this limitation the required tumour temperature can not be obtained. The recent advent of numerical models for simulation of electromagnetic waves in heterogeneous patient models and calculation of the temperature distribution in perfused tissues, enables accurate hyperthermia treatment planning. This thesis addresses the use of electromagnetic and thermal models for the improvement of hyperthermia applicators and treatment techniques.The use of absorbing blocks for the local reduction of hot spots is described. Rectangular absorbing blocks, consisting of agar boundsaline water, create a local attenuation of absorption maxima, but also cause a negative edge effect. This can be reduced by tapering of the edges, introduction of a waterlayer and by variation of the salinity of the block along its length. Regional hyperthermia treatment can be significantly improved by application of an annular, multi-ring, multi-antenna array, operating at 150 MHz. In this array applicator the power distribution can be controlled by phase-amplitude steering. Comparison with existing radiative and capacitive hyperthermia applicators shows that local pain can be reduced by phase-amplitude control and that a better temperature distribution in the tumour can be obtained.