Proton therapy offers a number of advantages over conventional X-ray radiotherapy. While both methods rely on ionization to damage cancerous cells and stop the spread of malignancy, protons can be "tuned" to deliver most of their energy at a specified depth. This reduces the chances of skin burns and cell damage to healthy tissue surrounding a tumour. Tailoring protons' energetic payload to the tumour target also increases the likely success of radiotherapy. (See also Practical moves on hadron therapy on medicalphysicsweb).
The high cost of particle accelerators compared with X-ray technology kept protons out of mainstream health care for many years. Interest is now growing in the technology, though, as evidenced by the opening of dedicated clinical proton-therapy facilities in the US, Japan and Europe. However, sites must generally find a dedicated room to house the accelerator, and then run multiple treatment rooms for the technology to be commercially viable.
In contrast, Still River Systems aims to sell pared-down proton sources that fit in a treatment room. "It's really a matter of reducing the size, cost and complexity of the accelerator itself," explained former radiation physicist Kenneth Gall, who co-founded Still River Systems in February 2004. "Our aim is explicitly to make this technology available to hospital-based treatment centres of any size, even community hospitals."
Still River Systems' endeavour is being financed entirely by private investment. The company currently has 30 full-time staff and several consultants on the payroll. It is also sponsoring a programme of design and development at the Massachusetts Institute of Technology (MIT).
The MIT team is providing the engineering know-how to realize Gall's vision, according to Timothy Antaya, co-principal investigator on the project. Antaya and colleagues at MIT's Plasma Science and Fusion Center are designing a unit that will accelerate protons up to 250 MeV but that can still be operated easily and safely by clinical staff.
"People in the nuclear-physics particle-accelerator industry don't really understand that, for a clinical device, you can't have a complicated system with lots of adjustable parameters that need to be continually reset," Antaya explained. "We also carefully defined all our clinical safety requirements and included these in the design engineering process."
Precise details of the development unit are being kept under wraps while patents are pending. However, it is known that protons will be delivered from a synchrocyclotron (a cyclotron in which the frequency of the driving RF electric field is varied to compensate for the mass gain of the accelerated particles as their velocity begins to approach the speed of light). This marks a departure from the usual choice of synchrotron or isochronous cyclotron as the particle accelerator.
"From a clinical standpoint, the proton beam it delivers will be the same as the proton beam from any other system. If it came out of a wall, you wouldn't be able to tell which accelerator was on the other side," Gall told medicalphysicsweb.
Marketing approval from the US Food and Drug Administration (FDA) has yet to be granted for the compact system. However, because proton therapy per se already has the FDA's assent, Still River expects that clinical trials will not be required (i.e. regulators need only be satisfied that the system can fire a proton beam, and that it is safe and effective).
In the absence of FDA clearance, Still Rivers Systems has entered into a contract with its first customer, Washington University, in St Louis, MO, to construct a one-room proton-therapy facility onsite. This is due to be installed early in 2008. Meanwhile, Tufts New England Medical Center, Boston, MA, has filed for state permission to commence using protons for cancer treatment, in anticipation of a favourable FDA decision.