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Linear accelerator machines (this page and far right) deliver high-energy X-rays to treat cancer

The healthcare world has already dipped its toe into modular construction. Modular doctors鈥� surgeries and hospitals are popping up all over the UK. Now it鈥檚 the turn of cancer treatment centres to join the off-site revolution. Europe鈥檚 first modular radiotherapy facility will open in February at the Mount Vernon Cancer Centre in Northwood, London.

A modular treatment centre has many benefits for the NHS but it also brings fresh challenges for the teams that install them.

The Mount Vernon centre was built when the hospital realised that it needed to replace six of its seven linear accelerators 鈥� the machines that deliver the high-energy X-ray beams used in radiotherapy. It also wanted two extra machines to deal with the increasing demand for cancer treatment. Four of the machines could be housed in the existing radiation-proof bunkers but a lack of space and new shielding requirements meant that new bunkers were needed for the remaining five machines.

Cash and time were at a premium. 鈥淎 five-bunker complex built traditionally from dense concrete would take 24 to 30 months to construct. Installation would take about two to three months and there would be six months鈥� commissioning time for each machine,鈥� says Kyle McClelland, the project鈥檚 director at West Hertfordshire Hospitals NHS Trust.

Instead, the new centre will be ready at the end of the month, having taken about 10 months in total. 鈥淔or the patients it means we can treat 4500 people in our building before traditional bunkers would have been finished. It鈥檚 mainly the fact they were made off site that has allowed us to do this,鈥� says McClelland.

Each of the five vaults is made from steel pods by American specialist Rad Technology. They were manufactured in Canada and shipped to the UK. Each is the same size as a standard international freight container and has the same lifting attachments for ease of transport. Each vault consists of 10 pods 鈥� five on the ground with five more stacked on top. The double-skinned steel walls of the pods are filled with aggregate, which forms a continuous layer around the wall, and which stops radiation leakage where the pods join. The pods are bolted together and joined with a weatherproof seal. There are control rooms for the machines and a set of offices and treatment rooms.

Off-site construction allowed the team to do several jobs at once. For example, while the building鈥檚 foundations cured, the linear accelerators were installed in the pods. Typically, installing each of the five accelerators would have taken three days but the team managed to install all five in just two-and-a-half days.

Accuracy was the key to the design, so site measured everything repeatedly. Back in the factory, the pods were precision-made so that they fitted on top of each other and joined together without gaps where radiation could leak. The 2.438 m wide pods had to be within 3.175 mm of their design size. The team more than met this requirement, building the centre to within 1.36 mm per pod.

The foundation slab the pods rest on had to be within 2 mm of designated measurements in order to avoid ripples, and had to be extremely flat so that the components on top fitted together. 鈥淭he only people who can make them that flat are people who build warehouses for robotic forklift trucks,鈥� says David Naylor, president of European operations at Rad Technology. For this job, the team chose contractor Geoffrey Osborne. Once finished, the foundation was so flat that the building did not need any shims to prop it up.

Most traditionally built radiotherapy centres have a corridor with two 90掳 turns called a maze. The turns stop radiation escaping as it only travels in straight lines. This corridor would have taken up valuable space on a small site and could have increased the cost of the project. Rad Technology鈥檚 solution was to have a door with a build-in radiation shield. The 10-tonne door hangs on three 20-tonne hinges. They are so well balanced that a child could push them open although they will be electronically operated when in use.

The design also saved the trust money. Under NHS rules, there must be an empty accelerator bunker for every four-and-a-half to five machines. Each bunker costs 拢1m to build and 拢100,000 a year for 10 years in depreciation and energy costs. The trust was already struggling to fund a 拢21m project on 拢7m of government grant 鈥� it later solved the problem with a sale and leaseback deal 鈥� so the expense of two empty bunkers was not a welcome prospect.

Rad Technology鈥檚 Fast Swap design means there is a chamber in the bunkers behind the machine where panels can be removed so that the machine can be lifted out of the building. 鈥淲e can remove the accelerator and install a new one over a weekend. You can鈥檛 do that in a traditional building,鈥� says Naylor.

The centre is due to move 35 miles to Hatfield in 2012 and Rad Technology will be there to lift the pods to the new site. 鈥淩eusing the pods rather than spending 拢25,000 on demolition [of a traditional bunker] and millions on rebuilding is much cheaper over the lifecycle of the building,鈥� says McClelland.

The project has garnered a whole range of healthcare firsts. As well as being the first off-site-built radiotherapy vault in Europe, it was the first in the world to use the Fast Swap device to avoid the need for an empty chamber, and its use of sales and leases to fund the deal has not been tried in the NHS for a radiotherapy vault outside PFI deals. McClelland rates it 鈥渢he best project I have ever worked on鈥�.