Intensity-Modulated Radiation Therapy (IMRT)
What Is IMRT?
IMRT is a type of external beam radiation therapy that uses advanced computer technology to plan and deliver precisely shaped radiation beams to a tumour. Unlike traditional radiation, IMRT modulates (controls) the intensity of each beam, allowing higher doses to the tumour while protecting nearby healthy tissues and organs.
How IMRT Works
A detailed 3D image of your tumor is created using CT, MRI, or PET scans.
Using this map, a customized treatment plan is developed to target the tumor from multiple angles.
Each radiation beam is adjusted in intensity and shape to match the tumor’s size, shape, and location.
Treatment is delivered in daily sessions over a few weeks, depending on your diagnosis.
Frequently Asked Questions
A medical linear accelerator (LINAC) generates the photons, or x-rays, used in IMRT. The machine is the size of a small car—approximately 10 feet high and 15 feet long. During the treatment, the patient must lie still. The intensity of each beam’s radiation dose is dynamically varied according to treatment plan. The patient will not feel any sensation while the radiation is on, but will hear noise from the machine, and may smell an odor from the electronic equipment, or see the warning indicator light. The noises and odors from the machine are normal. The patient will be in the room alone during treatment but is constantly monitored by the radiation therapists from outside the treatment room. The time in the treatment room depends on the specific plan, but usually is between 15 minutes and one hour
The radiation oncologist, a specially trained physician, first consults with the patient to determine whether IMRT is the most appropriate treatment. After obtaining informed consent, the individualized course of treatment is planned.
A radiation physicist, who has specialized training in the field of medical physics, ensures the linear accelerator delivers the precise radiation dose and that computerized dose calculations are accurate.
A dosimetrist works with the medical physicist to develop the IMRT plan and beam configurations necessary to deliver the dose prescribed by the radiation oncologist.
The final treatment plan is verified by the medical physicist on the treatment machine using a phantom (a device that simulates the human body) that measures the dose delivered by the treatment plan. This ensures that the dose planned by the radiation oncologist is the dose delivered by the machine.
A radiation therapist positions the patient on the treatment table and operates the machine.
The oncology nurse assesses the patient during the course of treatment and provides the patient with additional information about the treatment and possible adverse reactions. The radiation oncology nurse also helps in managing any reactions or side effects from treatment that may occur, in collaboration with the physician.
Before planning treatment, a physical examination and medical history review will be conducted. Next, there is a treatment simulation session, which includes CT scanning. A small mark or tattoo may be placed on the patient’s skin to help align and target the equipment. The radiation oncologist uses this scan to make an individual plan for the patient. In some cases, a mask or other device to keep the patient still during treatment will be made. Sometimes the patient is instructed to follow a certain bowel and bladder preparation regimen or to fast prior to the simulation and treatment. Intravenous contrast material may be injected during the CT scan to help define the tumor better.
Occasionally, additional scanning procedures, including positron emission tomography (PET) and magnetic resonance imaging (MRI), might also be required for IMRT planning. These diagnostic images can be merged with the planning CT and help the radiation oncologist determine the precise location of the tumor target.
In some cases, it is necessary to insert radio dense markers into the target for more accurate positioning. Typically, IMRT sessions begin about a week or two after simulation.
Radiation therapy, including IMRT, damages the DNA and stops cancer cells from dividing and growing, thus slowing or stopping tumor growth. In many cases, radiation therapy is capable of killing all of the cancer cells, thus shrinking or eliminating tumors. Radiation therapy may be used in conjunction with surgery (adjuvant radiation). In this scenario, radiation targets potential microscopic disease after surgery.
Intensity-modulated radiation therapy (IMRT) is an advanced mode of high-precision radiotherapy that uses computer-controlled linear accelerators to deliver precise radiation doses to a malignant tumor or specific areas within the tumor. IMRT allows for the radiation dose to conform more precisely to the three-dimensional (3-D) shape of the tumor by modulating—or controlling—the intensity of the radiation beam in multiple small volumes. IMRT also allows higher radiation doses to be focused on the tumor while minimizing the dose to surrounding normal critical structures. Treatment is carefully planned by using 3-D computed tomography (CT) or magnetic resonance (MRI) images of the patient in conjunction with computerized dose calculations to determine the dose intensity pattern that will best conform to the tumor shape. Typically, combinations of multiple intensity-modulated fields coming from different beam directions produce a customized radiation dose that maximizes tumor dose while also minimizing the dose to adjacent normal tissues.
Because the ratio of normal tissue dose to tumor dose is reduced to a minimum with the IMRT approach, higher and more effective radiation doses can safely be delivered to tumors with fewer side effects compared with conventional radiotherapy techniques. IMRT also has the potential to reduce treatment toxicity, even when doses are not increased. Due to its complexity, IMRT does require slightly longer daily treatment times and additional planning and safety checks before the patient can start the treatment when compared with conventional radiotherapy.
What types of cancer can be treated with IMRT?
IMRT is a highly versatile and effective radiation therapy technique used to treat a wide range of cancers. It is particularly beneficial in areas of the body where tumors are located close to critical organs or sensitive structures. Common cancers treated with IMRT include head and neck cancers, where precision is crucial to preserve functions like speech and swallowing. It is also widely used in the treatment of breast cancer, prostate cancer, and lung or thoracic tumors, where targeted radiation helps reduce damage to the heart, lungs, or surrounding tissues. Additionally, IMRT is effective for gastrointestinal cancers, gynecologic malignancies, and brain and spinal tumors, offering patients a safer and more precise treatment option with fewer side effects and improved outcomes.