Power and Precision: Proton Therapy Can Target Brain and Spine Tumors with Fewer Side Effects

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People with tumors of the central nervous system (CNS), which includes the brain and spinal cord, are living longer after treatment. This improvement is due to advanced surgical and radiation techniques and more-effective drugs. The increase in survival makes minimizing the treatment side effects that can impair day-to-day life even more important.

One way Memorial Sloan Kettering radiation oncologists are reducing side effects is through the use of a sophisticated form of radiation called proton therapy. Proton therapy kills cancer cells by damaging their DNA. The process is similar to the one used in conventional X-ray radiation. But while traditional radiation uses beams of X-rays, proton therapy targets tumors with charged particles, called protons.

The unique physical properties of protons allow them to deliver the radiation dose at a specific depth in the body. X-rays release their energy both before and after they hit their target. With proton therapy, all of the energy is released when it reaches the tumor, lowering the impact to normal tissue.

Greater Precision

Since joining MSK’s Department of Radiation Oncology in 2016, MSK radiation oncologist Jonathan Yang has used proton therapy to treat people with a range of brain tumors. These include gliomas, meningiomas (slow-growing, noncancerous tumors that form in the membranes that surround the brain), pituitary tumors, brain metastases (cancer that has spread to the brain from another part of the body), schwannomas (tumors of the tissue covering nerves), and leptomeningeal metastases (cancer that has spread to the space containing the brain, spinal cord, and cerebrospinal fluid). Often, these patients have previously been treated with X-ray radiation.

Dr. Yang says the precision of proton therapy can be critical for protecting the brain’s delicate tissues.

“While protons aren’t necessary for all brain tumors, they can offer an advantage over other types of radiation,” he says. “Proton therapy can limit the amount of normal brain tissue receiving radiation. That reduces the effects on important functions, such as vision and hearing.”

Scaling Up to Help More Patients

All MSK radiation oncologists carefully consider whether proton therapy may be appropriate for their patients. There remain some uncertainties with proton therapy, but it may offer an advantage over standard approaches some of the time. MSK is looking to increase the number of patients who may benefit from this advanced form of radiation.

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For example, CNS radiation oncology specialists consider using proton therapy on some brain tumors that have come back. Treating these cancers can be challenging depending on the location of the tumor. Often, people with these recurrent tumors have received significant radiation doses in the past to important parts of the brain. These may include optic nerves, which are critical to vision, and the brainstem, which regulates many essential body functions, such as breathing, heart rate, and swallowing.

The CNS team is also exploring proton therapy for some people with noncancerous tumors of the central nervous system. “People with these tumors survive for a long time, so it is even more important that we figure out ways to limit radiation doses to the normal brain tissue to reduce the potential for radiation-induced side effects,” Dr. Yang says. 

Another way to treat more people with proton therapy is by making the technology even more accessible. Since 2013, MSK patients have been treated at a proton facility in Somerset, New Jersey. In summer 2019, Dr. Yang and his colleagues will begin treating patients at the New York Proton Center. MSK is opening the state-of-the-art facility in Manhattan in collaboration with the Mount Sinai Health System and Montefiore Medical Center.

Researching New Approaches

Dr. Yang and colleagues are looking to further expand the use of proton therapy. They are designing clinical trials that test new approaches for other CNS cancers. One recently completed phase IB trial investigated whether proton therapy could be safely used to control leptomeningeal metastases to the brain and spine.

On occasion, people with this disease receive X-ray radiation to their whole brain and spine, Dr. Yang explains. This is done to sterilize the region and catch any cancer cells that might be floating through the fluid that fills the space. However, conventional X-ray treatment to the entire area is rather toxic. More often, doctors target the locations where cancer cells are causing symptoms or have formed a tumor. But with that approach, cancer cells can move to untreated areas within the space containing the brain, spinal cord, and cerebrospinal fluid. Once there, they clump together. This can cause headaches, nausea, vomiting, back pain, and weakness.

Patients in the recent trial received proton therapy to the entire space where leptomeningeal cancer cells can travel. The hope is that this treatment will reduce the cancer cells within that space and lower the chance of developing symptoms from leptomeningeal metastases after treatment. Proton radiation may be less likely to damage nearby organs, such as the heart and lungs, while treating areas around the spinal cord. Early results suggest that this technique is safe and potentially effective.

“This was the only trial in the country at this time testing this approach,” Dr. Yang says. “It was available only to MSK patients.” The next phase will take place at the New York Proton Center and will be open to patients from all three institutions.

MSK is also part of an ongoing multicenter phase III trial exploring proton therapy in people whose meningioma tumors have been removed by surgery. The study is meant to determine whether treating these tumors with proton therapy after surgery reduces the rate at which the cancer returns.

Dr. Yang expects more clinical trials testing proton therapy — either alone or combined with other treatments — for CNS cancers to begin at MSK as evidence of its effectiveness mounts. 

“MSK really is at the forefront of developing new approaches for these diseases,” he says. “And we want to generate data to expand proton therapy to help more people.”