For good measure – ensuring accurate dosimetry24 November 2014
As new technological healthcare treatments, such as proton therapy, are developed, and existing technologies are fine-tuned and adapted to more applications, the importance of accurate dosimetry – ensuring the patient is exposed to exactly the right amount of treatment – is enormous. Richard Booth explains the efforts of national measurement institutes to develop highly accurate standards of measurement, and how this can improve patient outcomes and quality of life.
Public healthcare is charged with improving rates of patient diagnosis and treatment while simultaneously managing austerity-driven budget and resource cuts. To achieve this, the therapies and medical devices used for diagnosis and treatment need to be underpinned by reliable, safe, cost-effective and highly accurate measurements.
This is where national measurement institutes (NMIs) have a critical role to play. These are world-leading centres of excellence in developing and applying the most accurate measurement standards, science and technology available. The UK's NMI is the National Physical Laboratory (NPL) in Teddington, which has developed and maintained the nation's primary measurement standards for more than a century. These standards are behind the National Measurement Systems' infrastructure of traceability throughout the UK and the world that ensures accuracy and consistency of measurement. Ultimately, the cutting-edge measurement science and technology delivered by NPL help to enhance economic performance and the quality of life.
NPL's work is particularly relevant to the UK's healthcare industry. Using accurate measurement and optimised detection methods right from the start of the research and development process ensures companies make informed decisions and receive useable results faster and with greater confidence. NPL's healthcare research covers diagnostics, medical physics and health and well-being where measurement plays a vital role in ensuring reliable and robust detection, diagnosis and treatment. Medical research underway at NPL includes a project to measure drug distribution within cells for more efficient drug development, temperature mapping of feet to aid the treatment of diabetes-related conditions, and a technique for screening for breast cancer using ultrasound.
One area in which NPL's measurement work is having a direct impact on contemporary healthcare is through its role in underpinning cancer therapies, in using measurement to ensure the medical devices treating cancer patients are performing to a safe and effective level.
Radiotherapy is a critical tool in the fight to treat cancer. It uses ionising radiation such as high-energy X-rays or electron beams, to destroy cancer cells. In 2011, the UK's National Radiotherapy Awareness Initiative showed that 52% of all cancer patients would benefit from access to radiotherapy (it is currently 35-43%).
Radiotherapy is involved in 40% of cases where cancer is cured. It is second only to cancer surgery and is the primary treatment in 16% of all cancer cures, whereas chemotherapy is only 2%. Radiotherapy is also highly cost-effective, costing up to £4,000 for a complete fractionated treatment in comparison with £7,000 for surgery and approximately £17,000 for a course of chemotherapy.
Every hospital needs to ensure that its radiotherapy equipment is stable and accurate because delivering correct radiation doses is critical. If the dose is too low, the cancer may continue to grow. If it is too high, healthy tissue could be damaged. NPL has the highly accurate measurement facilities and expertise to support radiation dosimetry for cancer therapy.
Apply the technology
In 2008, NPL installed a state-of the-art clinical linear accelerator (linac) facility to replace its aging industrial linac. This was primarily to support radiation dosimetry for cancer therapy to help ensure patients are treated with accurate doses of radiation. This was followed in 2013 by a second clinical linac facility - officially opened by Sir Mark Walport, the UK Government's chief scientific adviser.
The first clinical linac to be installed at NPL was manufactured by Elekta and is the same as those installed in many hospitals to provide radiotherapy treatments. However, unlike any hospital machine, the one at NPL can be reconfigured to deliver seven different photon energies - instead of the standard two or three energies found on a clinical machine - and ten electron energies. It can also deliver image-guided 4D radiotherapy, in which tumours can be targeted more accurately.
The second clinical linac represents the culmination of a unique partnership between the Department for Business, Innovation and Skills, Elekta and NPL. It is maintained by Elekta and fitted with the newest technology ahead of its introduction onto the market. The new linac provides excellent research opportunities to drive forward the development of measurement science in the area of radiation dosimetry. This facility extends the National Measurement System's commitment to respond to healthcare challenges, specifically improving the treatment of cancer.
The clinical linacs combined with the use of primary standards developed at NPL combine to provide accurate doses that enable calibrations with smaller uncertainties. This allows hospitals to deliver more accurate, and more effective, radiation doses to cancer patients. The acquisition of the clinical linacs has reduced the time it takes to calibrate equipment.
The dose in every radiotherapy treatment provided by UK hospitals is determined by instruments calibrated directly against the NPL primary standard. This results in a world-leading national dosimetry system that underpins the rapidly expanding variety of radiotherapy technologies.
Highly accurate measurement facilities are essential to provide confidence in calibration across the healthcare sector, but new research is just as critical. NPL works with partners to conduct and publish new research to help improve the accuracy of radiotherapy as a cancer treatment. For example, in 2012, NPL published the results of a collaborative project in the journal Medical Physics, which was selected as a highlight by the journal's editor.
In this paper, NPL and its partners at Canada's McGill University and the University of Montreal reported a misconception on how charged particles are distributed locally while delivering a uniform dose to a tumour using a specific form of radiotherapy called 'intensity modulated radiotherapy' (IMRT). Identifying this misconception allowed for much improved correction factor calculations for ionisation chambers and other detectors used in IMRT, and therefore will safeguard cancer patients who receive this form of treatment in future.
As treatment therapies using both radiation and ultrasound are developed to allow for more targeted treatment, the need to develop more robust measurement and testing requirements around these technologies is critical.
One example is proton therapy for cancer treatment, which has been high on the news agenda following the case of Asyha King. What has not been overly reported is the government's investment of up to £250 million into this treatment. The aim of this funding is to treat 1,500 patients a year across two dedicated centres at University College London Hospital NHS Foundation Trust and the Christie NHS Foundation Trust in Manchester. As for all radiotherapy systems, these should be capable of delivering a dose to the tumour volume to within 3-5% of that prescribed.
Proton therapy is a form of treatment that can help reduce the dose to healthy tissue surrounding cancerous cells when compared with conventional radiotherapy. Yet the properties of protons that make this possible also make this therapy more susceptible to uncertainties in the treatment plan and delivery than with conventional therapy. It is a considerable challenge to achieve this level of dose accuracy in proton therapy. For conventional therapy, the effect of uncertainties in treatment planning and delivery is to smear the dose distribution in a patient. However, similar uncertainties for proton therapy can result in significantly compromised tumour coverage and/or increased dose to normal tissue, thus severely limiting the full potential of proton therapy.
To guard against this, it is essential that the UK has a robust system for supplying trained and experienced staff, robust treatment plans and delivery verification techniques. Measurement will again have a critical supporting role to play here, building on expertise and past research in proton therapy dosimetry developed by measurement scientists collaboratively with the radiotherapy community.
The confidence that accurate measurement can provide medical devices is not restricted to a specific instrument or type of therapy. Ultrasound is the long established treatment of choice for kidney stones, many soft tissue injuries and a range of surgical applications including cataract surgery. New therapies using ultrasound are also emerging, with more than 40,000 prostate cancer treatments using high-intensity focused ultrasound (HIFU).
However, while patients and doctors assume that HIFU treatments are based on a good understanding of the required dose in tissue (as in radiotherapy), the measurement infrastructure for similarly reliable treatment planning does not yet exist. This is why NPL is leading DUTy (Dosimetry for Ultrasound Therapy), a European research project to establish a global metrology infrastructure for ultrasound exposure and dose to tissue that will enable more effective and safer treatments across the spectrum of conditions.
There are several promising new uses of ultrasound (as well as HIFU) that need metrology to take them from the periphery into mainstream practice where they can deliver maximum benefit. These include:
- Enhanced bone healing: low intensity pulsed ultrasound (LIPUS) shows a 30% reduction in the time to regain full weight bearing, which is a reduction of about 40 days.
- Essential tremor treatment: this condition affects ten million people in the US. In a trial using non-invasive ultrasound through the skull at the University of Virginia, the first ten patients showed 92% improvement in functional activity.
- Targeted drug delivery: with ultrasound it is possible to direct drugs to specific organs and stimulate uptake, even opening the blood-brain barrier.
The DUTy project will help progress all these uses of ultrasound. It will lead to improved equipment, clinical procedures and regulations, bringing health and financial benefits to patients, healthcare professionals and medical device manufacturers. It will help to herald a new era of less invasive cancer therapies, reduce healthcare costs and enable technology developers to bring new modalities to market faster.
Measurement expertise in medical physics for radiation and ultrasound-based therapies will ensure companies and practitioners can develop safe and effective treatment plans that bring more rapid treatments and reduce patient side effects. NMIs such as NPL will continue to work in partnership with companies to ensure that their products meet the required testing and safety standards for their introduction into the healthcare system and then provide the recognised standards to ensure their ongoing effectiveness.