Proton therapy uses charged particles to target tumors with precision while reducing the risk of treatment-related side effects.
Traditionally, particle accelerators have been used to conduct elaborate physics experiments by propelling charged particles at very high speeds. In addition, some medical centers, including Memorial Sloan Kettering, employ these massive machines to produce molecules for PET imaging. But these giant devices have another important use: creating cancer-fighting energy in the form of a proton beam to kill or shrink tumors while minimizing harm to healthy tissue.
Proton therapy, a highly sophisticated form of radiation, is currently available at only 14 locations in the United States. In the fall of 2013, MSK physicians began using proton therapy at a facility in Somerset, New Jersey, to treat a variety of cancers under the leadership of Oren Cahlon, MSK’s Director of Proton Therapy, and radiation oncologist Nancy Y. Lee, Vice Chair for Experimental Therapeutics. Dr. Lee also serves as the medical director and president of the New York Proton Center (NYPC), an affiliation of three New York City hospitals, including MSK.
Here, Dr. Lee explains how proton therapy delivers its dose so precisely and why it represents a leap forward in patient care.
How does proton therapy work, and how does it complement more conventional radiation therapies?
Traditional radiation uses beams of x-rays, which are waves of high-energy light. MSK has always been at the forefront of developing ways to optimize this treatment. In fact, over the last 15 years MSK radiation oncologists, including myself, have been leaders in showing the benefits of intensity-modulated radiation therapy (IMRT), a technique that targets tumors with multiple beams at different angles and intensities that now is widely used.
Proton therapy, by contrast, targets a tumor with charged particles, called protons. While proton therapy kills cancer cells through a process similar to that used in x-ray radiation — by damaging their DNA — the unique physical properties of protons allow them to deliver the dose at a specific depth in the body. With proton therapy, all energy has been released when it reaches the tumor site, so there is no dose beyond that point. This lowers the impact to normal tissues surrounding the tumor and reduces the risk of treatment-related side effects. There also are hints that proton therapy may work on recurrent tumors that are resistant to conventional radiotherapy, although this has not been confirmed.Back to top
What types of tumors can be treated with proton therapy?
Proton therapy is most useful for localized cancers that have not spread from the original site. We have used it most often for head and neck tumors and for pediatric cancers. Head and neck tumors are surrounded by many critical structures, such as the brain stem, spinal cord, optic structures, tongue, and esophagus, so it’s essential to confine the particles to the cancerous tissue. Proton therapy is also beneficial for pediatric cancers because developing tissues in children are incredibly sensitive to radiation.
Other cancers also lie near important organs or tissue. When treating breast cancer, you obviously don’t want to damage the heart, and in some patients, proton therapy can reduce unwanted exposure to that area.
In fact, proton therapy might be useful for any disease site and is increasingly being considered as an option for all cancer types. In addition to the cancers I already mentioned, our doctors are using it to treat select spinal tumors, soft tissue sarcoma, prostate cancer, and lung cancer.Back to top
Have you already seen a reduction in side effects in patients receiving this therapy?
In our patients with salivary cancer in particular, there has already been a noticeable benefit. Almost all of these patients used to lose their sense of taste and have soreness on the inside of their cheek following conventional treatment, but it does not seem to happen with proton therapy. More broadly, we are conducting a study that compares side effects of proton therapy with IMRT in patients with head and neck cancer, and our preliminary findings indicate those treated with proton therapy have a better quality of life.Back to top
Is proton therapy covered by insurance?
Many insurers recognize that proton therapy has proven effective. It is covered by Medicare and by many of the private insurance companies for things like pediatric cancers and brain tumors, and in patients requiring re-irradiation [radiating new tumors that emerge in the same location as tumors that already received radiation]. However, for many diagnoses, it is dependent on the particular insurer, the patient’s benefits, and the clinical scenario. Sometimes the patient’s physician needs to communicate with a physician at the insurance company in order to obtain approval.Back to top
What are the most common misconceptions about proton therapy?
Probably the biggest is that this technology is new or investigative. Patients actually have been treated with proton therapy in the United States for several decades, but it has been limited to a handful of centers. Another misconception is that the actual treatment experience is dramatically different from x-ray radiation. In reality, proton therapy typically involves the same number of treatments with the same session times as conventional radiation therapy, and the day-to-day experience is indistinguishable. I continue to be a very strong proponent of IMRT, but it’s important that patients realize proton therapy is now an option through MSK.Back to top