What is Proton Therapy

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Science of Proton Therapy FAQ

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What is proton therapy?

Proton therapy is an advanced and highly precise form of radiation treatment. It allows our doctors to focus radiation directly into the tumor, minimizing damage to surrounding tissue and the risk of short- and long-term side effects from treatment. Currently available at only a small number of centers in the United States, including ours, proton therapy is beneficial in treating a broad range of tumors, including those of the brain, central nervous system, gastrointestinal tract, head and neck, left breast, lung, and prostate, as well as sarcomas and certain childhood cancers. Please see the Cancers Treated section of our website for a more comprehensive list.

Research has repeatedly shown higher doses of radiation are associated with better cure rates. But as the dose increases in standard X-ray treatment, there is greater damage to healthy tissue and complications (side effects) increase dramatically. This is because X-rays lose most of their energy just as they penetrate the skin, and continue to lose energy on the way to the tumor and beyond. Protons, on the other hand, release most of their energy in the tumor rather than when they first enter the body.

Protons are charged particles rather than beams of energy. The energy distribution of protons can be directed and deposited in tissue volumes designated by our radiation oncologists. Protons are energized to specific velocities which determine how deeply in the body protons will deposit their maximum energy. Additionally, the maximum interaction with electrons occurs as the protons approach their targeted stopping point. Thus, maximum energy is released within the designated cancerous area. This greater control and precision of treatment protects surrounding healthy cells from excess radiation, lessening short- and long-term side effects.

How is proton therapy different from standard radiation treatment?

Proton beams deposit much of their energy directly in the tumor, reducing damage to healthy tissue and allowing patients to receive higher, more effective doses. Less damage to healthy tissue and organs can result in fewer side effects than are sometimes experienced with standard X-ray radiation therapy, thus improving patients' quality of life and long-term health. X-ray radiation can be harder to control and deposits more radiation in healthy tissue as it enters and leaves the body.

Why is proton therapy a good option for children with cancer?

Since their bodies are still growing, children are more sensitive to damage to healthy tissue caused by radiation. Proton therapy’s precision reduces the amount of radiation to healthy tissues. Therefore proton therapy can reduce the side effects children suffer from radiation, such as growth and developmental problems, as well as secondary tumors later in life. Our center has a radiation oncologist who specializes in proton therapy treatment for children.

Are X-rays as effective as protons in destroying tumors?

X-rays and protons can be equally effective in destroying cancer tumors. The difference is that X-ray treatments damage more healthy tissue in the process. X-rays release their maximum dose of radiation soon after penetrating the skin, potentially damaging healthy tissue and organs on their way to the tumor and again as they pass through the body beyond the tumor. Protons can be precisely directed to release most of their energy when they reach the tumor. Because there is much less exposure to healthy tissue with protons, a higher dose often can be delivered, leading to more effective treatment.

Why is proton therapy often considered a more precise treatment option compared to standard X-ray radiation therapy?

Because proton beams deposit more of their energy directly in the tumor, less radiation reaches the healthy tissue in front of the tumor, and almost none reaches the healthy tissue behind the tumor. Patients often experience fewer short- and long-term side effects that typically accompany standard X-ray radiation therapy. In addition, because more radiation can be deposited directly in the tumor, a higher dose can often be delivered, leading to more effective treatment.

Is proton therapy experimental?

No. Proton therapy was approved by the Food & Drug Administration for clinical use in 1988. It has been used worldwide on over 100,000 patients.

What kind of cancers does proton therapy treat? Who could benefit?

Patients with tumors in locations near critical structures and vital organs benefit most from proton therapy. Proton therapy has a broad applicability to a number of solid tumor sites: brain, lung, prostate and many childhood solid tumors. Patients who suffer from recurrent tumors or who have exhausted other treatment options can also benefit from proton therapy.

Proton therapy is especially important for children because children are more sensitive to radiation effects in the long term. A pediatric radiation oncologist is particularly interested in how to treat a child’s tumor with radiation while avoiding exposure to the healthy tissue. For example, when a child is diagnosed with a brain tumor, it is imperative to avoid irradiating the child’s growing brain. This is important because the healthy part of their brain needs to continue to develop as the child gets older and by using proton therapy we can minimize the effects that may impact their learning in the future.

How does proton therapy protect healthy tissue?

Protons are charged particles rather than rays of energy. With X-rays, radiation goes in the body and exits out the other side of the body. Proton therapy radiation goes into the body, releases its energy at the tumor and stops right there. There is no exit dose.

The energy distribution of protons can be directed and deposited in tissue volumes designated by our radiation oncologists. Protons are energized to specific velocities which determine how deeply in the body protons will deposit their maximum energy. Additionally, the maximum interaction with electrons occurs as the protons approach their targeted stopping point. Thus, maximum energy is released within the designated cancerous area. This greater control and precision of treatment protects surrounding healthy cells from excess radiation, lessening short- and long-term side effects.

How do you target the tumor?

Since every tumor is different, the Care Team starts by doing a scan of the patient to see exactly where the physician needs to deliver radiation and what parts he or she needs to avoid with the radiation. Then our physicists, dosimetrists and radiation oncologists work together to make an individualized treatment plan that maps out the direction, angle and dosage of the proton beam.

What is PBS?

PBS stands for Pencil Beam Scanning. PBS is a relatively new innovation within proton therapy that can "paint" a tumor with a very thin, very precise beam of protons that is accurate within millimeters. PBS sends rapid pulses of protons to each planned spot within the tumor until the whole tumor is treated. “PBS is the most advanced way to deliver proton radiation and allows us to more precisely sculpt protons to treat more complex tumors, such as in the head and neck, lung, abdomen, and pelvic areas,” says Smith “Jim” Apisarnthanarax, MD, radiation oncologist at the center.

Who receives PBS?

PBS is usually used for patients with complexly-shaped tumors because it allows doctors to better shape the proton radiation. SCCA Proton Therapy offers PBS in the gantry, which allows doctors to target and treat tumors at nearly any angle. SCCA Proton Therapy also offers PBS in our fixed-beam room for treating prostate cancer. 

Can proton therapy be used in combination with other cancer treatments?

In many cases, yes. Proton therapy can be used in combination with chemotherapy, as a follow up to surgery and in combination with X-ray radiation. Our physicians can talk to you about what other treatments you might need in conjunction with proton therapy.

How many proton therapy centers are there, and how many patients have received proton therapy?

As of February 2017, there are 25 proton therapy centers operating in the United States, with many more in planning and construction stages. Worldwide, more than 130,000 patients have been treated with proton therapy.

Do government safety regulations exist for proton therapy centers?

Yes. Proton therapy centers fall within state and federal regulatory statutes that require all radiation-production facilities to be licensed. SCCA Proton Therapy meets the standards required federally and within Washington State. The regulations are the same as those for X-ray therapy.