Volumetric Modulated Arc Therapy (VMAT)

Volumetric modulated arc therapy (VMAT) is a type of external beam radiation therapy (EBRT) that treats cancer. With EBRT, a machine sends radiation beams to destroy tumors. The radiation destroys cancer cell DNA, causing the cells to die. During VMAT, the machine’s arm rotates around you while you’re lying down. The arm delivers continuous doses of radiation toward a tumor. The machine never touches your body.

Unlike older forms of EBRT, VMAT can send energy beams of different strengths toward the tumor as the arm encircles you. The beams can be as small as 2.5 x 5 millimeters, roughly the size of a pencil tip. This allows healthcare providers to send high doses of radiation toward tumors without exposing the surrounding healthy tissue to harmful amounts of radiation.

VMAT is a common cancer treatment, largely because of its pinpoint precision. It’s also fast. It only takes a few minutes to deliver powerful doses of radiation.

What cancers are treated with VMAT?

The precise delivery technique makes VMAT a good option for treating tumors close to vital organs. For example, your cancer doctor (radiation oncologist) may recommend VMAT if you have a tumor wrapped around an organ.

It’s most often used to treat:

• Brain cancers
• Head and neck cancers
• Lung cancers
• Prostate cancers

It also treats other types of cancers and even noncancerous tumors.

What happens before VMAT?

Your cancer care team will use imaging to map the tumor’s location in relation to healthy tissue. This helps them design treatment that safely targets the treatment area.

During a planning session called simulation (“sim”), your care team will prepare you for your treatment session. It’s like a test run that doesn’t involve the actual radiation. They may:

• Position you so that the machine can send radiation directly to the tumor
• Make tiny markings on your skin to position you accurately for the radiation treatments
• Fit you with a mask to shield you from radiation
• Make molds or casts that help you stay still during treatment

Sim may take place during a single session. Or it may require a few visits.

What happens during volumetric modulated arc therapy?

A radiation therapist will position you as you were during sim. They’ll operate the machine from a separate room. They may refer to this machine as a linear accelerator or LINAC. You’ll be able to communicate via a two-way microphone the whole time.

Here’s how it works:

1. The arm of the machine will rotate slowly around you in a circle. The arm is called the gantry. As it rotates 360 degrees around you, it adjusts the shape and strengths of the beams. You won’t feel the beams.
2. The radiation therapist will monitor your treatment. They’ll ensure that you’re getting the right amount of radiation in the right spots.
3. The machine will finish rotating. A single rotation is called an arc. It usually only takes one or two arcs per session to deliver a full radiation dose.

Afterward, most people go home and resume their routine.

How long does VMAT treatment take?

A session takes about 20 minutes. It only takes around two minutes for the LINAC machine to deliver the radiation. Most of the session involves a radiation therapist getting you into the right position.

Depending on your diagnosis, you may need daily VMAT treatment sessions for several weeks. Ask your oncologist about your treatment schedule.

How long will it take for me to feel better?

Everyone’s experience is different. You may have mild side effects but feel better shortly after treatment ends. Or you may need a few months to recover.

Because VMAT spares healthy tissue from harmful radiation, you’re less likely to have major side effects. Still, some cell damage can’t be avoided. Most VMAT side effects impact the part of your body that gets direct radiation.

Ask your oncologist what to expect based on your health and treatment plan. They can also help you manage side effects, so you feel better sooner.

When should I call my healthcare provider?

You’ll see your provider during follow-up appointments to check on your progress. Come prepared to ask questions about how treatment is working. Let them know how you’re feeling. Be sure to report any side effects.

What is the difference between VMAT and IMRT?

VMAT (volumetric modulated arc therapy) is a type of IMRT (intensity-modulated radiation therapy). Both techniques destroy tumors by sending customized doses of radiation that target cancer cells. The difference is in how the radiation machine targets tumors.

With IMRT, the arm of the machine stops and points. When it does, it sends high doses of radiation to various sites in the treatment area.

With VMAT, the arm constantly rotates. As it moves in a circle, the machine adjusts the shape (dosage) of the beams. The beams strike the tumor with maximum strength without exposing healthy tissue to harmful doses of radiation.

What are the side effects of VMAT?

The side effects of VMAT are the same as in other forms of radiation therapy. Common side effects include:

• Fatigue
• Nausea and vomiting
• Diarrhea
• Headaches
• Hair loss
• Itchy, dry, red, swollen or peeling skin

The side effects depend on which part of your body receives the radiation. For example, it’s common to have skin changes. But they usually only show up in the treatment area.