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Three ways to make proton therapy affordable – Nature Weekly Journal

by Thomas R Bortfeld & Jay S Loeffler

If cost was not an issue, proton therapy would be the treatment of choice for most patients with localized tumours. Protons can be targeted more precisely than X-rays¹, so the tissues around the tumour receive two to three times less radiation. This lowers the chance of causing secondary tumours² or impairing white blood cells and the immune system³. High doses of protons can be delivered safely to hard-to-treat tumours: for instance, those at the base of the skull or in the liver. Such accuracy is crucial when treating cancers in children.

Yet most hospitals do not offer proton therapy. The equipment is huge and expensive. Housed in multistorey buildings with halls the size of tennis courts, one proton centre with 2–3 treatment rooms typically costs more than US$100 million to build. To reach deep-seated tumours, the protons must be sped up to 60% of the speed of light (a kinetic energy of 235 megaelectronvolts; MeV) using a particle accelerator, such as a cyclotron or synchrotron. Rotatable gantries with wheels typically 10 metres across and weighing 100–200 tonnes direct the protons at the patient from a range of angles. Concrete shields, metres thick, are necessary to block stray neutrons.

“Nothing so big and so useless has ever been discovered in medicine,” said Amitabh Chandra, director of health policy research at the John F. Kennedy School of Government at Harvard University in Cambridge, Massachusetts. He has compared a proton-therapy system to the Death Star from Star Wars.

Nonetheless, there are now more than 60 proton-therapy centres around the world, with 26 in the United States alone. Almost half of them (12) treated their first patient within the past three years. But construction delays and closures are also common. The companies that build the facilities and the investment groups that own them are increasingly struggling to make a profit. The Scripps Proton Therapy Center in San Diego, California, filed for bankruptcy in March, just three years after opening its doors.

What has gone wrong? Patient charges are high, often three to four times more than the priciest X-ray treatments. Fewer patients are being treated with protons than was anticipated: common diseases such as prostate cancer can be cured as effectively using other forms of radiation and surgery⁴. And in the United States, major insurance companies are denying proton therapy to up to 30% of eligible patients⁵ on the basis that there are too few rigorously designed and completed clinical trials providing evidence of better outcomes. In our experience, however, this is a vicious cycle: such trials are difficult to conduct when patients are denied private health coverage⁵.

The solution is to make proton-therapy facilities smaller and cheaper, with costs of around $5 million to $10 million, similar to high-end X-ray systems. A dozen ‘miniaturized’ facilities are in operation. We have installed one at Massachusetts General Hospital in Boston. Now academics, private researchers and investors need to make proton-therapy systems even smaller and more competitive so that more patients can benefit.

Shrinking infrastructure

Proton-therapy technology is much more compact today than it was a few decades ago⁶. Superconducting magnets can confine protons in a tighter space. The weight of accelerators has gone down from hundreds of tonnes to less than 20, and their diameters have shrunk by a factor of 3 since the early 1990s. The smallest therapeutic accelerator so far is less than 2 metres in diameter — about the same footprint as a king-sized bed.

Yet, combined with the gantry and other equipment needed, even the most compact systems for sale today occupy a couple of hundred square metres. This is much larger than a conventional treatment room of 50 square metres. Most hospitals lack the money and space to construct a special building for proton therapy.

We have been testing how smaller systems can be squeezed into existing hospital buildings, working with the proton-technology vendor ProTom International in Wakefield, Massachusetts, and engineers at the Massachusetts Institute of Technology in Cambridge. Getting an accelerator and gantry into two basement X-ray rooms in our central Boston hospital cost about $30 million, less than one-third of the cost of a dedicated centre but still about five times more than a top-end X-ray unit.

Both the equipment and the price tag need to shrink further if proton therapy is to replace X-rays. Fitting the facility into one room is the goal. This would allow hospitals to simply replace existing X-ray equipment with proton units without building work. Getting there will be technically challenging, even with rapid advances in magnets