Proton Therapy Glossary of Terms


Beam Transport System – The beam transport system is a series of electromagnets that steer the beam. The protons from the cyclotron are transported to each treatment room using a vacuum line.

Benign Tumors – Benign tumors are not cancerous. They can often be removed, and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body.

Bragg Peak – The point at which protons (and other heavy charged particles) deposit most of their energy. When protons travel through matter, they lose energy and gradually slow down. Just before they come to rest, they deposit their peak energy.

CT Scan – Computed tomography, also known as a CT or CAT scan, is a painless, noninvasive way to see inside of the body using X-ray imaging. During a CT scan, multiple images are taken from different angles. A computer combines the images to create digital cross-sectional images, or slices, of soft tissue, organs, blood vessels and bone. The slices can often be combined to create 3-D pictures.

Chemotherapy – Chemotherapy for cancer involves the use of drugs (taken orally or intravenously) to attack cancerous cells, directly or indirectly, with the goal of killing them or slowing their growth.

Cyclotron – The cyclotron generates the proton beam using hydrogen and oxygen to create a plasma stream. Protons are extracted, accelerated to roughly 100,000 miles per second, and then sent to the beam transport system. The cyclotron weighs approximately 95 tons.

Dosimetrist – Dosimetrists have special training in measuring radiation exposure and prescribing appropriate doses of radiation. Physicists and staff dosimetrists collaborate with your physician to design a treatment plan. They also monitor the radiation treatment machines for proper operation and accuracy.

Gamma Knife – Gamma Knife radiosurgery is a type of radiation therapy used to treat malignant and benign tumors. It has been shown to be beneficial for the treatment of some noncancerous conditions, including functional disorders such as arteriovenous malformation (AVMs) and trigeminal neuralgia.

Gantry – Three of California Protons Cancer Treatment Center’s treatment rooms are equipped with a gantry, which rotates around the patient 360 degrees to allow treatment from any direction. Each gantry is three stories tall and weighs 283 tons.

Immobilization Device – A device used to correctly and comfortably position a patient during treatment so that the patient’s setup is stable.

Intensity-Modulated Radiation Therapy (IMRT) – IMRT is an advanced form of 3-D conformal radiotherapy that allows the clinical team to specify the dose of radiation for the tumor while restricting the dose to surrounding tissues. IMRT is used most often to treat prostate, head and neck, and other tumors near critical organs and tissues that are free of cancer.

Malignant Tumors – Malignant tumors are cancerous and are made up of cells that grow out of control. Cells in these tumors can invade nearby tissues and spread to other parts of the body.

Medical Oncologist – A physician who specializes in the diagnosis and treatment of cancer. After a cancer diagnosis is made, it is the oncologist’s role to explain the cancer diagnosis and the meaning of the disease stage to the patient; discuss various treatment options; recommend the best course of treatment; deliver optimal care; and improve quality of life both through curative therapy and palliative care with pain and symptom management. The medical oncologist also prescribes and delivers systemic therapy and chemotherapy when indicated.

Metastasis – The spread of a cancer or disease from one organ or part of the body to another not directly connected with it. Sometimes cells move away from the original (primary) cancer site and spread to other organs and bones where they can continue to grow and form another tumor at that site. This is known as metastasis or secondary cancer.

MRI – Magnetic resonance imaging, also known as an MRI, is a painless imaging procedure used to help diagnose a wide variety of conditions. The MRI scanner uses a powerful magnet, radio waves and computer technology to produce pictures of organs, soft tissues, bone and most other internal body structures from all angles, without using ionizing radiation.

Passive Scattering – Traditional method for delivering proton therapy in which the shaping of the beam to conform to the tumor takes place just outside of the treatment nozzle.

Pencil Beam Scanning – The latest in proton therapy technology, pencil beam scanning allows a precise dose of proton therapy to be delivered to a tumor. The technology limits radiation exposure to surrounding tissue. The pencil beam can be used to treat solid and complex cancerous and noncancerous tumors in adult and pediatric patients.

PET Scan – Positron Emission Tomography, also called a PET scan, is an imaging technique that examines the metabolic function of cells. It can be used for diagnosing and tracking the progress of a disease or condition. During a PET scan, a radioactive substance called a tracer is given intravenously. Some types of cells – such as cancer cells – may metabolize this substance faster than the surrounding healthy cells. Using advanced imaging technology, the PET scan shows the areas of abnormal metabolism to help pinpoint where a disease is originating in the body and how it is progressing.

Photon – A tiny particle of light or electromagnetic radiation. X-rays and gamma rays are photon radiation.

Prostate-Specific Antigen (PSA) – Prostate-specific antigen (PSA) is a protein produced by prostate cells. The PSA test is done to help diagnose and follow prostate cancer in men.

Proton/Proton Radiation – A proton is a positively charged particle found in the nucleus of an atom. The protons used in proton therapy are derived from stripping a hydrogen atom of its electron. Proton radiation is a form of external-beam radiation treatment, delivered by generating a beam that penetrates the body from the outside. When protons interact with electrons in the atoms of cancer cells, they impart energy that damages the DNA of the cancer cell. This destroys specific cell functions, including the ability to divide or proliferate. A cancer cell’s ability to repair such injuries is generally inferior to that of cells in normal tissues. As a result, cancer cells die, as does the tumor.

Proton Therapy – Proton therapy is a type of radiation treatment that uses protons (subatomic particles) instead of X-rays to treat cancerous and noncancerous conditions. It can target tumors with great precision, decreasing damage to healthy nearby tissue and organs and reducing the risk of secondary cancers caused by radiation exposure.

Radiation Oncologist – A physician who is trained to treat cancer with radiation and will make recommendations regarding your treatment. Radiation oncologists also treat some benign diseases with radiation.

Radiation Therapist – Radiation therapists are trained and licensed to deliver radiation treatments, administering radiation under a physician’s prescription and supervision. They also arrange patients’ daily schedules, monitor patients throughout each radiation treatment, maintain daily records and perform quality assurance checks on the radiation machines to ensure that they are working properly.