Definition and Overview

Intensity-modulated radiotherapy (IMRT) is an advanced form of radiotherapy. It uses modern technology that allows doctors to shape the radiation beams to match the shape of the tumour. Other forms of radiotherapy only match the beams to the width and height of the tumour. This causes damage to a wider area of healthy tissues near the abnormal growth. With IMRT, beams are focused on the tumour. Thus, doctors are able to increase the dosage during treatment. The higher the dosage, the better are the treatment outcomes.

IMRT requires careful planning and relies heavily on imaging technologies. These include magnetic resonance imaging (MRI) and 3D computed tomography (CT) scan. These tests are used to carefully calculate the pattern of dose intensity based on the shape of the tumour.

IMRT takes longer because of its complexity. It requires numerous safety checks before it can be started. However, it offers better results. It does not only kill cancer cells, it also minimises damage to normal tissues. This leads to fewer side effects and complications.

Who Should Undergo and Expected Results

IMRT can be used in patients with cancers of the prostate, head, and neck. The list also includes cancers of the spinal cord and brain. In some cases, it can also be used to treat cancers of the breast, lung, and thyroid. It can also be used in patients with gastrointestinal and gynaecological cancers.

IMRT is used to kill cancer cells. Its goal is to prevent abnormal cells from growing and dividing. In many cases, IMRT is enough to dissolve the tumour. This means that patients may not need additional cancer treatment.

Radiation therapy comes with side effects. These are often caused by damage to surrounding tissues. Patients often complain of severe abdominal pain and diarrhoea. Many also develop throat and mouth ulcers. These side effects are significantly reduced by IMRT because it spares normal tissues near the tumour.

How is the Procedure Performed?

Patients with cancers mentioned above are carefully assessed to make sure that they qualify for IMRT. Their oncologist (cancer specialist) will run a number of tests before the procedure. Patients are also informed about the benefits and possible side effects of the treatment. Doctors will also discuss other details, such as the length of treatment and special preparations required to initiate IMRT.

IMRT is delivered by a specially trained team of doctors and specialists. These include:

  • Radiation oncologist - A doctor specialising in cancer treatment using radiation therapy.

  • Medical physicist - Medical physicists play a crucial role in IMRT delivery. They are responsible for formulating techniques for the precise measurement of radiation dosages.

  • Dosimetrist - A dosimetrist is responsible for calculating the dose of radiation. He or she ensures that it is enough to kill cancer cells.

The team will start by identifying the exact location of the tumour. Using 3D scans, the radiation oncologist will map the tumour and surrounding healthy tissue. This information is used by the physicist to make calculations. The goal is to shape the radiation beams to match the shape of the tumour. He or she will ensure that the linear accelerator will deliver the precise radiation dose. Working with a dosimetrist, the physicist will ensure that the computerised calculations are accurate. They will also work together in making adjustments to ensure that they will be able to deliver the exact dose prescribed by the radiation oncologist.

The planning stage can take several hours to a couple of days. It may involve the design of devices to help patients stay in the same position during each session. Doctors may also elect to create blocks that can be placed in the delivery system. This can help further protect healthy tissues.

Before the treatment, marks are placed on the patient’s skin. These help ensure that the patient stays in proper position throughout the procedure. The patient is guided onto the treatment table. Doctors will then take high-quality images using CT scan or x-rays. This helps ensure that the patient’s position is right. If not, doctors will have to make adjustments and take images again.

The linear accelerator will then deliver radiation beams as per the team’s plan. The beams are delivered in about 300 different segments. They are focused on the tumour, which reduces the dose of radiation passing through the normal tissues surrounding the growth.

Patients often require multiple sessions in order to achieve the desired results. The number of sessions depends on the location, size, and type of the abnormal growth. In many cases, patients undergo treatment five days a week for up to eight weeks. Each treatment session can last between 10 and 30 minutes.

During the treatment, patients will meet with their medical team at least once a week. Doctors will run tests to determine how patients are responding to the therapy. They will also address the concerns and questions of the patients. Patients may also receive treatment for their side effects.

After treatment, patients are scheduled to return within a few weeks or months for follow-up care.

Possible Risk and Complications

IMRT is painless. However, as the treatment progresses, patients may start to feel side effects. The most common are fatigue and skin problems. Skin in the treatment area may become swollen and irritated.

Other side effects include hair loss in the treatment area, problems with swallowing, and headaches. The list also includes nausea and vomiting, lack of appetite, and urinary problems.

IMRT can also cause late side effects. These can occur months or years after the treatment. However, they are very rare. These include infertility, secondary cancer, and fluid build-up in some parts of the body. Depending on the location of the tumour, patients may also notice changes in the function of their vital organs. These include the brain, kidneys, lung, spinal cord, and colon.


  • Stanford Health Care.


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