What is Proton Therapy?

Proton therapy is an advanced type of radiation therapy that uses “protons” rather than X-ray “photons” to deliver radiation to the tumor. In conventional radiotherapy, the photon beams can deposit radiation and damage healthy cells as they pass through the body. Proton therapy deposits most of the radiation directly at the tumor site, resulting in less damage to healthy tissue and fewer side-effects.

Proton Therapy vs. Conventional Radiation Therapy

Conventional radiation therapy uses X-ray photon beams to deliver radiation to the tumor. These photon beams gradually release radiation as they pass through the body’s healthy tissues and organs and move towards and through the tumor. This excess radiation can damage these healthy tissues and cause side effects, which may limit the dose of radiation a patient can safely receive.

With proton therapy, doctors can deliver much higher levels of radiation to the tumor, with a lower risk of side effects. Unlike photons, which release energy gradually, protons travel to a precise point where they then release the majority of their energy. Doctors can control the proton beam so that most of the radiation is deposited directly at the tumor site, and healthy tissues beyond the tumor are spared as the beam move through the body. Doctors can also control the shape of the proton beam to conform to the shape and depth of the tumor. After the radiation is released at the tumor site, no more radiation is released beyond the range of the proton particles.

Benefits of Proton Therapy

Proton therapy may be especially beneficial in the following cases:

• Hard-to-reach or irregularly shaped tumors that are located near or in critical organs or structures. Proton therapy can be conformed to the size, shape, and depth of the tumor, and releases the bulk of radiation directly at the tumor site, allowing nearby healthy tissue to be spared.
• Pediatric cancers. Children are very sensitive to the harmful effects of radiation, as the body’s organs are still developing. Children are also more susceptible to the long-term effects of radiation therapy such as secondary cancers, hormone deficiencies, and cognitive deficits. Proton therapy damages less healthy tissue than conventional radiation therapy, and can greatly reduce these side effects.
• Recurrent tumors or tumors that have stopped responding to chemotherapy. Depending on the size, location, prior therapy, and specific type of tumor, proton therapy may offer patients with recurrent or resistant tumors another option.

What to Expect during Proton Therapy

Patients will receive a highly specialized care plan from a team of experts, including:

• radiation oncologists
• physicists
• dosimetrists
• nurses
• anesthesiologists
• radiation therapists
• social workers
• dieticians

These experts will work together to develop a care plan that is highly customized to each patient’s disease.

• About 1-2 weeks before the first treatment session, patients will attend a pre-treatment “simulation” procedure to plan the specifics of treatment.
• The patient may be fitted with an immobilization device to restrict motion and help guide the beam during the procedure. The therapist may also mark the skin or immobilization device with special ink to help aim the proton beam at the tumor.
• The patient is positioned in the immobilization device on a robotic bed in the treatment room. The doctor then conducts imaging tests to determine the exact location, size, and shape of the tumor. The entire simulation process may take about 45 minutes to 1 hour.
• The doctor uses this information to create an optimal treatment plan. The doctor will calculate the radiation dose and position of the beam, and may develop a custom “aperture” or opening for the beam to pass through that conforms the beam to the shape of the tumor.
• During a treatment session, the patient is again positioned in the immobilization device, in the exact same position as during the simulation procedure. The radiation therapist, who administers the radiation treatment, then leaves the room and the patient is moved into the gantry, which is a large rotating donut-shaped device, about 35 feet wide. Due to the finite range of the proton particles, it is essential that the patient is positioned for treatment as precisely as at time of simulation. Therefore, the doctor will confirm that the patient is in the correct position by taking a series of low-energy X-ray images and comparing them with treatment set-up images generated from the simulation scans.
• The gantry rotates around the patient, directing protons toward the tumor. The procedure lasts about 30-90 minutes, and the patient neither feels nor hears the procedure.
• The typical course of proton therapy varies depending on the tumor type and stage. Usually, a standard course of treatment is two to eight weeks, one treatment daily, five days per week.
• Side effects of protons are generally fewer than conventional radiation but include hair loss, fatigue and nausea. Other complications may arise depending upon the area being radiated, for example stomach ulceration if within the treatment field.