By Joanne Conroy, MD
I may be one of the few people in America who is glad that the Mayo Clinic is building two proton facilities. I know Ezekiel Emanuel and Steven Pearson called this “crazy medicine and unsustainable public policy in their recent New York Times post. And yes, I know that each facility costs more than $180 million.
However, this field has much to teach us about less invasive methods of killing cancer cells. We won’t make those discoveries unless we invest in the technology and perform the clinical studies. Germany’s government has financed proton research for 20 years and has published some dramatic improvements for survival rates in specific pediatric tumors.
A very brief 411 on the theory from a non-expert:
External beam radiation (photon therapy administered by many U.S. hospitals) works by damaging the DNA via indirect and direct damage. Indirect damage is a result of the ionization of water, forming free radicals that then damage the DNA. Direct damage is caused by breaking the DNA.
Unfortunately, often only one of the DNA strands is damaged, leading to slower cell death or mutation because these cells have mechanisms for repairing single-strand DNA damage. Photon beams are most effective on tumors cells that are rapidly dividing.
Photon beams damage normal tissue. The concentration of the beam is shaped through a 3D approach by aiming the beam from several angles to intersect at the tumor, providing a much larger absorbed dose than in the surrounding, healthy tissue.
What we really need is a radiation beam that would not affect normal tissue and that would ensure damage to both DNA strands.
Enter protons and carbon.
Due to an energy distribution known as the Bragg peak, protons and carbon ions can be made to deliver the bulk of their impact at a particular depth within tissues. The dose increases while the particle penetrates the tissue, up to a maximum (the Bragg peak); then it drops to about zero. These beams can be targeted to minimally affect surrounding normal tissue.
The heavier carbon ions make an even more potent beam and have a better chance to damage both DNS strands, so many institutions are preparing their new facilities to deliver carbon ions as well as proton beam.
It is expensive and the science is still in its adolescence, but think about the potential applications — for example, the ability to diagnose and pinpoint a tumor precisely and then eradicate it with a beam of energy. While this sounds strangely like the use of the tricorder and the treatment methods in the sick bay on the Starship Enterpise, think of what we could save on costs, morbidity, and mortality for open surgical procedures.
So yes — I am glad that academic medical centers are committing to understanding the science and exploring these new technologies. Isn’t that what we are supposed to do?
—Joanne Conroy, MD is Chief Health Care Officer at the Association of American Medical Colleges. Follow her on Twitter @joanneconroymd.