Proton therapy, also referred to as, 'proton beam therapy,' is a type of radiation treatment that uses protons instead of X-rays to treat cancer. A proton is a positively charged particle. At high energy, protons have the ability to destroy cancer cells. Doctors might use proton therapy by itself, or they may combine it with standard radiation therapy, chemotherapy, surgery or immunotherapy. As with standard X-ray radiation therapy, proton therapy is a type of external-beam radiation therapy. It is painless and delivers radiation through the person’s skin from a machine outside of their body.
Proton therapy or proton beam therapy is defined as a medical procedure, a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. Proton therapy's main advantage over other types of external beam radiotherapy is that as a charged particle the dose is deposited over a narrow range and there is minimal exit dose. Because proton beams can be delivered in higher doses and with far more accuracy, proton therapy typically can control cancer with fewer treatments than intensity-modulated radiation therapy (IMRT). Fewer treatment complications mean that physicians can deliver higher doses of proton radiation to cancer sites, and an increased dose of proton radiation can improve the chances for a successful outcome.
A machine called a, 'synchrotron,' or, 'cyclotron,' speeds up the protons. The speed of the protons reflects their high energy. The protons travel to a particular depth in a person's body based upon their energy.
After the protons reach the desired place in the person's body, they deposit the specific radiation dose in the person's tumor. With proton therapy there is no radiation dose beyond the tumor. In contrast, X-rays continue to deposit radiation doses as they exit the person's body. What this means is that radiation is also damaging nearby healthy tissues, possibly causing side-effects.
People often times receive proton therapy in an outpatient setting. What this means is treatment does not require an admission to a hospital. The number of treatment sessions depends on the stage and type of cancer. At times, doctors deliver proton therapy in one to five proton beam treatments, usually using larger daily radiation doses. This is commonly referred to as, 'stereotactic body radiotherapy.' If a person receives a large, single dose it is sometimes called, 'radiosurgery.'
Planning for Treatment
Proton treatment requires planning. Prior to treatment, the person undergoes a computed tomography (CT) or magnetic resonance imaging (MRI) scan. During the scan, the person is placed in the exact same position that will be used for treatment. Doing so requires the doctor to limit a person's movement as they are scanned.
To help keep the person in one place, they might be fitted with a device which restricts their movement. The type of device depends on where the person's tumor is located. A person might; for example, need to wear a custom-made mask for a tumor in their brain, eye, or head.
The person will also need to wear the device later for the radiation planning scan. The table on which the person lies for the radiation planning scan permits the scan to be referenced to the marks on the person's body or the immobilization device. This helps to ensure the person's position is accurate during every proton treatment.
The immobilization devices are designed to fit snugly so there is no motion during the radiation treatment. The radiation oncology team; however, wants each person to be as comfortable as they can be during treatment. It is important for people to communicate with their team to find a comfortable and reproducible position for treatment. Some people – especially those with tumors around the neck and head, feel somewhat anxious when they need to lie still in an immobilizing device. It is important to let the members of the oncology team know if this causes you to be anxious. A doctor may prescribe medication to help you relax for the treatment planning scan as well as the treatments.
Using the radiation treatment scan, a member of the person's oncology team draws the tumor area or areas to be treated. They also draw the tissues to be avoided. The process is similar to the one for planning radiation therapy using X-rays.
Forms of Cancers Treated with Proton Therapy
Proton therapy is used in the treatment of tumors which have not spread and for tumors near important portions of the body such as near the brain, eye and spinal cord. It is also used for treating children because it decreases the chance of harming developing tissue that is healthy. Children might receive proton therapy for cancers of the brain and spinal cord or the eye - such as orbital rhabdomyosarcoma and retinoblastoma. Proton therapy might also be used to treat the following cancers:
Treatment is delivered in a treatment room. For every treatment, a member of the person's team will bring them into this room. A team member will place the person into the immobilization device on the treatment table. For some areas around the neck and head, such as the person's eye, the person is positioned in a chair instead of being on a table.
The treatment team takes great care to make sure the person is in the right position prior to starting treatment. This involves the use of alignment lasers centered on marks placed on the person's body, or the immobilization device, at the time of the treatment planning scan. A member of the team takes X-rays or CT scan images before each radiation treatment to ensure the person is in the exact same position as the treatment planning. The reason why is so the protons hit the tumor and not the tissues surrounding the tumor.
Some proton treatment rooms are equipped with what is called a, 'gantry.' The gantry rotates around the person, ensuring the radiation is delivered to the tumor from the best angles to treat the cancer. During the person positioning process, the person might notice the gantry will also be rotated around them so the radiation delivery, 'snout,' from which the protons emerge is in the desired position.
After the person has been accurately positioned, the members of the radiation oncology treatment will leave the treatment room and go to the treatment delivery controls outside of the room. The oncology members will have the ability to see and hear the person with video equipment mounted in the treatment room. The team uses the treatment program controls on the machine console outside the treatment room to deliver the person's proton treatment.
The protons leave the cyclotron or the synchrotron machine. Magnets then direct them to the person's tumor, at times using the gantry. During the treatment, the person must remain still to avoid moving the tumor out of the focused proton beam.
The treatment itself is painless. Afterward, the person might experience skin issues and fatigue, to include redness, irritation, dryness, swelling, blistering and peeling. The person might experience additional side-effects, particularly if they are also receiving chemotherapy. The side-effects of proton therapy depends on the portion of the person's body being treated, the size of the tumor, the types of healthy tissue next to the tumor, as well as whether or not the person receives chemotherapy at the same time. The person's radiation oncology doctors and nurses will discuss which side-effects are more likely for them.