The use of proton and ion beams to treat cancer was invented by a former LBNL scientist, and the Laboratory was a longtime leader in its development.
Practically since the discovery that ionizing radiation can kill cells, doctors had been exploring ways to use it for cancer therapy without invasive surgery. In many institutions, including Berkeley, they tried many forms of radiation and many ways of delivering it, with varying degrees of success.
Robert Wilson, an E.O. Lawrence protégé who had recently left the Berkeley Radiation Laboratory for Harvard (and would later become the founder of Fermilab and a Nobel laureate) had the seminal idea behind modern proton and ion therapy in 1946. Protons, he knew, are steerable (unlike neutrons) and, when penetrating matter, deposit most of their energy within a small distance near the very end of their travel (unlike x- and gamma rays). This phenomenon is known as the “Bragg peak” after its discoverer.
Wilson realized that by selecting the energy of the beam so that the Bragg peak occurred within the tumor, doctors could spare healthy tissue en route to and beyond it. He also knew that it was possible to form small proton beams and guide them precisely. He had this idea at a time when particle accelerators capable of reaching the necessary energies were becoming more widely available, and a number of institutions began exploring it. Animal experiments at the “Rad Lab” confirmed his predictions in 1948, and treatment began here in 1954, first at the 184-Inch Synchrocyclotron and then at the Bevalac.
|An energy deposition phenomenon called the Bragg peak is the key to ion-beam therapy.
The Bevalac (a 1974-onward combination of the SuperHILAC heavy-ion linac and the Bevatron) enabled clinical trials with heavy ions rather than the proton and helium beams used previously. All in all, more than 1400 cancer patients were treated at what is now LBNL before the Bevalac was decommissioned in 1993.
By that time, the Food and Drug Administration had approved proton therapy as a treatment option for certain cancers, and hospital-based proton centers would soon follow. There are now some 70 proton centers worldwide, 14 of them in the US. The number of patients treated worldwide is of order 100,000.
Making proton treatment facilities better remains attractive to hospitals, and meanwhile, the US is moving to rejoin the exploration of potential benefits of heavier ions such as carbon – a form of therapy pioneered at LBNL.