Ultrasound is a long established treatment for medical conditions, including kidney stones, soft tissue injuries and cataracts. The last decade has seen a dramatic increase in uses of ultrasound which use very high power levels as a surgical and therapeutic tool. An inability to measure accurate ultrasound doses for these new clinical treatments could lead to potential over, or under, exposure for the patient. This might cause harm or fail to deliver the anticipated benefit, thus hampering the introduction of new ultrasound curative or restorative treatments.
New applications include:
- High Intensity Focused Ultrasound (HIFU) using tissue ablation for treating cancer as a stand alone therapy or in combination with radiotherapy and chemotherapy
- lower intensity ultrasound for stimulating bone repair and ultrasound treatment for strokes
- focused ultrasound through the skull for the treatment of degenerative disease.
In order the exploit the potential of these new techniques, there was a pressing need to develop the metrological framework to support well specified, traceable quantities for expressing exposure and dose.
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.
The traceable dosimetry frameworks developed by this project will make it possible to determine dose-response curves and arrive at robust, personalised treatment plans which maximise the benefits and reduce the undesirable side effects.
The work benefits medical equipment manufacturers and regulators who need measurement standards to allow them to bring new equipment to market that complies with the European directives. It also helps to establish a more homogenous global regulatory and purchasing environment.
Development of the metrology framework for new ultrasound techniques gives healthcare providers a greater choice of reliable therapies and allows for more comparison of data and tailored treatment plans. It is anticipated that the measurement standards and methods developed will provide the basis for rigorous treatment planning of the emerging therapies. This will lead to better, and potentially cheaper, disease management, including less invasive treatments with fewer side-effects and shorter recovery times.
This was an EMRP project, find out more on the project: Dosimetry for ultrasound therapy (HLT03 DUTy).