DIAGNOSTIC EQUIPMENT
particularly as it was to be located in the basement of a large London hospital (UCH). The Gamma Knife machine itself weighs approximately 20 tonnes, and the source changer used to load the sources weighs around 15 tonnes. The installation thus required reinforced floors, the closure of wards above, and delivery through a false wall in the treatment room. Generally, the requirements for housing a Gamma Knife include ease of access, but the QSRC was a specific case, being ideally located in proximity to Queen Square ‘Imaging’ and Great Ormond Street Hospital.
Two different crane types Access to the centre presented as an issue, with two different types of cranes used, and all buildings below evacuated during delivery. With the equipment being so heavy, the biggest crane in Europe was used for the QSRC installation, which also involved a road closure via Westminster City Council. Transporting live radioactive sources is heavily regulated, and in addition, the installation was carried out during the 2012 London Olympics, which caused additional security concerns, further restricting access. The siting of a Gamma Knife centre
is also, of course, influenced by the associated facilities required, such as Imaging. A real advantage to operating a Gamma Knife facility is regular and efficient access to imaging. Arguably the most important part of this treatment is the planning – mapping out the lesions, and determining where to target the Gamma Knife. The QSRC is in fact optimally located, with the Queen Square Imaging Centre on the same premises. Although the technology is always
evolving, the physical technology behind Gamma Knife has been used for decades. The factor that enables this treatment to be as ‘cutting edge’ and precise as it is is the ability to plan where to target the Gamma Knife – a crucial element of the treatment process. One of the key purposes of enhanced diagnostic imaging (for example on a 3T MRI) is to better identify the overall volume and target, in order to treat more accurately and successfully. This is proving an exciting quality development introduced at QSRC this year. As imaging possibilities advance, and developments are made in MRI technology, this directly progresses the potential of Gamma Knife to become even more precise. This being said, the Gamma Knife machines are designed with very few moving parts. The key cobalt sources are housed within eight moveable sectors in the radiation unit that move forwards and backwards over pre-drilled holes in the tungsten, that allow radiation to reach the patient during treatment. This apart, the patient table is the only other moving part of the Gamma Knife, allowing for
74 Health Estate Journal September 2023
The Queen Square Radiosurgery Centre was established in 2012, and joined the Amethyst Group in 2020.
99% uptime. With a service contract and preventative maintenance provided by the machine commissioning body, Elekta, components are replaced on a time- cycle basis, and accuracy configuration is checked regularly. This generally takes place once per quarter out of hours when the clinic is empty. The service and maintenance of the machines therefore tends to be straightforward, and at current capacity, they can comfortably treat 1,000 patients per year.
Constant evolution The Gamma Knife machines undergo a process of ongoing evolution, with new developments regularly introduced to improve ease of use. The most significant recent developments have included the release of the Icon model in 2015, the new Vantage frame in 2018, and new planning software released in 2020. The Icon model introduced the ability to offer both frame treatments and mask-based treatments, with the first addition of cones being used in the machine, as well as allowing for fractionated treatments. The release of the Vantage frame, meanwhile, introduced a frame that was MRI-compatible, allowing for clearer imaging for treatment planning. The Vantage frame therefore
complements the plan optimiser software, Lightning, that was released in 2020 by Elekta. Also released at this time was remote planning software which allows for remote planning (and thus made continuing treatments easier during COVID). Not only does this eliminate the need for clinicians to physically be on site to plan a patient’s treatment, but it also gives them the ability to choose the duration and conformality of treatments. Clinicians can therefore offer more bespoke treatment sessions for their patients, which is particularly useful when treating more frail patients, or those who are in the later stages of their cancer journey.
Operational direction Providing Gamma Knife treatment therefore entails operational direction and
co-ordination. Multiple imaging sessions per patient, specialised clinical training, long treatment periods, and exposure monitoring for staff, can present implementation and treatment delivery challenges – especially considering the volume of patients seen with the cancer treatment backlog resulting from COVID. QSRC has witnessed considerable growth in the volume of metastatic cases referred for Gamma Knife treatment. Post-COVID, the Centre is seeing many more patients with multiple metastases, and this is where Gamma Knife can offer particularly effective treatment compared with other platforms.
Ian Paddick
Ian Paddick is lead physicist at Queen Square Gamma Knife Radiosurgery Centre. He has 24 years’ experience in Gamma Knife physics, including the commissioning of 10 B/4CPerfexion/ Icon models, bunker design, and Stereotactic MRI. He has also been involved in the clinical start week of over 100 Gamma Knifes. He won the Fabrikant Award at the 2022 ISRS (International Stereotactic Radiosurgery Congress) held last June in Milan, the first recipient of this award from the UK.
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