A preliminary study of therapeutic domain for bone tumor using ultrasound hyperthermia

This work applies a simplified model (a cone with convergent/divergent shape) to examine the optimal driving frequency, specific absorption ratio (SAR), and therapeutic domain for application of ultrasound hyperthermia to treat the bone tumor. The total ultrasound energy followed the exponential law for attenuation and uniform ideal power deposition within the cone-shape model. The relationship between the optimal driving frequency and correspondingly treated tumor size and depth was evaluated. To deliver the ultrasound energy into the tumor site and to avoid the potential damage to the normal tissue as much as possible, the ratio values of SAR distributions have to meet the criteria of SAR in bone tumor site being 3 times higher than the SARs in surface skin, bone marrow and bone. This criteria has been used to find the proper heating domain of ultrasound driving frequency and therapeutic tumor diameter in the authors' model. The results demonstrated that the optimal driving frequency depends on the density ratio of bone to tumor, tumor depth; ultrasound absorption of bone marrow, and diameter of bone, whereas independent of the acoustic window area and SAR ratio. The temperature distributions can verify the SAR ratio criteria in this simplified model.