The use of absorbing structures during regional hyperthermia treatment

Local pain is the main factor that limits regional hyperthermia treatment. Using th SAR model of the regional hyperthermia treatment planning system, the capability of absorbing blocks to reduce peripheral hot spots was inves tigated. The effect of rectangular absorbers of various size and salinity o n an elliptical phantom in the Coaxial TEM was evaluated. The computed resu lts were compared with SAR values measured in the phantom. Absorbers of 9x9 x4 cm(3) and a salinity of 18 gram l(-1) provide a SAR reduction in the mus cle equivalent material, centrally under the absorber of at least 50% at a depth of up to 3 cm. The effect on the central (i.e. tumour) region is less than 20%. Larger absorbers have a more global effect and cause more attenu ation in the central region. The attenuating effect depends strongly on the thickness of the fat layer between muscle and absorber. More than 2 cm fat limits the effective use of absorbers. Absorbers can induce a significant increase of SAR in muscle and fat near their edges. This effect also depend s on absorber size and salinity and the thickness of the fat layer. The eff ect of an absorber was also evaluated with a patient anatomy, yielding resu lts in agreement with the phantom experiments.