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Enhancing the efficiency of VMAT with Versa HD™

Vivian Cosgrove
9 June, 2014  
Partnership working between global human care company Elekta and the Leeds Cancer Centre is achieving clinical breakthroughs using pioneering and innovative technology
Vivian Cosgrove PhD
Head of Radiotherapy Physics, Leeds 
Cancer Centre, St James’s University 
Hospital, Leeds, UK
Leeds Cancer Centre is one of the largest cancer treatment centres in Europe, serving a catchment population in Yorkshire of 2.8 million. The centre, located in the Bexley Wing of St James’s University Hospital, opened in 2008. Radiotherapy facilities include ten Elekta linear accelerators,  three Siemens CT-simulators with 4DCT capability, a dedicated brachytherapy suite with theatres for high-dose-rate (HDR) treatment and 125I seed implants, and an Xstrahl orthovoltage (kV) unit. Now over 7500 new radiotherapy treatment courses are delivered per annum in Leeds.
In addition to the state-of-the-art  clinical service provision, a research suite was also established in the Centre, comprising two Elekta Synergy linear accelerators. The radiotherapy research facility has provided a platform for developing and evaluating novel radiotherapy equipment and delivery techniques.  One of the research linear accelerators is used primarily for radiation physics research and equipment development in partnership with Elekta. The second accelerator is used for translating these developments into clinical research programmes and ultimately into routine clinical practice. This was instrumental in establishing a stereotactic ablative body radiotherapy (SABR) programme in Leeds for the treatment of inoperable non-small cell lung cancer.(1) Leeds now has, by far, the largest clinical service for this treatment in the UK, having treated over 600 patients to date with the technique. 
Volumetric modulated arc therapy
An early focus of the research programme was the development of volumetric modulated arc therapy (VMAT). VMAT is a fast, efficient and effective way of delivering intensity modulated radiotherapy (IMRT). IMRT is a technique whereby the MLC in a linear accelerator is used to modulate the intensity profile of the radiation delivered to the patient.(2) This allows improved shaping and targeting of the radiation dose compared with standard ‘conformal’ treatment approaches. VMAT delivers intensity modulated beams while the gantry of the linear accelerator arcs around the patient. This can significantly reduce the time required to deliver a course of treatment.
It was recognised in 2010 that the uptake of IMRT in the UK was lagging behind much of Europe. This led to a number of initiatives to increase the availability of IMRT throughout the UK, so that at least 24% of all radical treatments were delivered using IMRT.(3) In Leeds, calculations based on initial experience of using ‘step-and-shoot’ (fixed gantry) IMRT indicated that delivering 24% IMRT would place the service under a lot of pressure due to the increased time required to deliver a fraction of IMRT compared to the standard ‘conformal’ treatment technique (see Table 1). However, the evaluations on the research accelerators demonstrated that VMAT would actually reduce the time taken to deliver a course of treatment, consistent with the experience of other early adopters of the technique.(4) 
Therefore, as a strategy to increase patient access to IMRT in the Leeds Cancer Centre, and achieve better utilisation of the available equipment, a programme to upgrade linear accelerators in the centre to deliver VMAT was implemented. This was completed in 2013, helped in part by the national Radiotherapy Innovations Fund.(5) 
The Agility™ multi-leaf collimator 
Another key developmental project that was carried out in Leeds  in partnership with Elekta was the evaluation and clinical implementation of the first Agility™ multi-leaf collimator (MLC).(6,7) The Agility™ is a complete redesign of the linear accelerator treatment head and has a number of unique features that have brought improvements to the delivery of VMAT. This includes field shaping over a maximum field size of 40cm x 40cm with 160 leaves that can individually move by up to 6.5cm per second. Prototype versions of the Agility™ were tested and evaluated with Elekta engineers on-site in Leeds using one of the research accelerators. The final production head was installed in January 2012 and received CE marking in April 2012, when first clinical treatments started in Leeds.  
One of the main objectives of the work was to use the Agility™ to deliver SABR treatments for inoperable non-small cell lung cancer (NSCLC) using VMAT. SABR is an advanced radiotherapy technique that enables high doses of radiation to be precisely targeted to a tumour volume with a sharp dose fall-off beyond the volume, thereby reducing the dose to normal, healthy tissue. Radiotherapy can then be delivered in high-dose, ‘hypo-fractionated’ sessions. In terms of local control and survival, there is now considerable non-randomised evidence supporting SABR as being superior to conventional radiotherapy for medically inoperable NSCLC.(8) This is achieved with less visits to hospital (between three and eight) compared with a conventionally-fractionated, radical radiotherapy approach (up to 30). 
Initial work using the Agility™ and VMAT demonstrated that lung SABR treatments could be delivered much quicker than standard SABR with fixed conformal beams (see Table 2). Standard SABR might require seven fixed beams and eight-to-nine minutes of ‘beam-on’ time, whereas SABR with Agility™ VMAT typically required around three minutes beam delivery time. The reduced delivery time was found to be more tolerable for patients while minimising the risks of patient movement during treatment. Therefore the technique was seen to improve the overall patient experience of the treatment as well reduce clinical risks. 
Flattening filter-free high-dose rate mode delivery
A further project carried out in partnership with Elekta was the development of flattening filter free (FFF) delivery for clinical use. By removing the flattening filter from the treatment head of a linear accelerator, dose rates two-to-three-times greater than those of standard, flattened beams can be achieved.(10) Advanced treatment planning technology can then be used to modulate the non-flat, high-dose rate treatment beams, so that highly conformal VMAT dose distributions can be achieved but with a reduced delivery time. 
Again, SABR VMAT treatments were prioritised for the high-dose rate, FFF treatment deliveries. The high doses per fraction (up to 16Gy) were considered ideally suited to benefit from the higher dose rates now achievable. Initial experience demonstrated a reduction in treatment ‘beam-on’ times down to less than two minutes for an 11Gy irradiation (Table 2). High-dose rate, VMAT SABR treatments began clinical use in Leeds in February 2013. One of the first patient treatments was featured on the Al Jazeera documentary programme ‘The Cure’.(11) 
The Versa HD™
Elekta unveiled the new  Versa HD™ linear accelerator in March 2013.(12) The Versa HD™ has brought together the Agility™ and high-dose rate, FFF technology, in addition to improved image guidance capabilities. Soon after the unveiling, negotiations commenced between Leeds Teaching Hospitals NHS Trust, Elekta and Medipass Healthcare Ltd, the managed equipment service provider to Leeds Trust. This provided an opportunity to bring forward the schedule of the PFI equipment replacement programme, leading to the installation of two Versa HD™ units in Leeds. The first Versa HD™ went into clinical use in July 2013, while the second followed in November. 
The first Versa HD™ has already had a significant impact on clinical workflow. Up to 60 patients per day are scheduled for treatment on the new machine. Treatment slots are booked at ten minute intervals so that up to six patients can be treated per hour. Initially, patients undergoing radical prostate radiotherapy have been prioritised for treatment, all with high-dose rate VMAT. In addition, the process to move all SABR treatments to high-dose rate VMAT has begun. Patients’ have their SABR treatment scheduled to a 20 minute time slot on the Versa HD™. 
In September 2013, over 25% of all radical treatments were delivered in the Leeds Cancer Centre using IMRT and VMAT. This equates to approximately 90 new patients starting advanced radiotherapy treatment every month. In addition, between 20 and 25 new patients also start a course of SABR treatment each month. The growth in these numbers has been greatly enhanced by the opportunities to develop the techniques, delivery equipment and workflow on the research accelerators, side-by-side with the clinical service. 
The ambition for the Leeds Cancer Centre has been to make advanced radiotherapy available for more of our patients. The release of the Versa HD™ and the early adoption of the new accelerators in Leeds have supported further improvements in the technical delivery of radiotherapy while also increasing productivity and efficiency. This will help us in our work both to increase patient access to radiotherapy and to improve clinical outcomes following treatment. 
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  10. Georg D, Knöös T, McClean B. Current status and future perspective of flattening filter free photon beams. Med Phys 2011;38(3):1280–93.