The EMRP project Dosimetry for Ultrasound Therapy developed a dose concept for therapeutic ultrasound, based on the absorbed ultrasound dose and cumulative quantity absorbed, rather than based on the thermal dose. Phantoms are useful in many areas of medical ultrasound as they can be scanned or exposed to evaluate and analyse the performance of ultrasound devices. In this project, phantoms were developed to mimic the response of human tissue, allowing the dose concepts to be tested. Ultrasound causes temperature in the treated tissue to increase, and is a key quantity to measure. The project developed ways to determine the temperature precisely, using a thin-film thermocouple and a phantom, during and after an ultrasound exposure. Together, the dose concepts, measurement techniques and the phantoms provide the basis for the metrological framework for therapeutic ultrasound doses.
The propagation of ultrasound is different in bone, compared to soft tissue, making treatment of cancers situated behind the ribcage particularly difficult. A 3D printed rib phantom was made and used to test ultrasound dose and treatment planning software. Complex modelling enabled scientists to calculate scattering off the rib surfaces and heating.
The project developed test methods based on an infra-red camera to assess heating, allowing commercial machines in use in hospitals and treatment centres to be assessed and compared. This will increase the efficacy of treatments, while minimising undesirable side effects, such as heating of healthy tissue. Making dosages more accurate means that individual treatment plans can be developed that take into account anatomical information and individual characteristics.