Department of RadiotherapyOur Techniques ❯ Image-Guided Intensity Modulation Radiation Therapy (IG-IMRT)


What is IMRT?
Intensity Modulated Radiation Therapy (IMRT) is an advanced radiation treatment technique that allows us to deliver radiation to a tumour with more precision, resulting in potentially fewer side effects and higher cure rates. IMRT utilizes thousands of tiny radiation beams entering into the body from different angles to intersect on the tumour.

What is Image-Guided Techology?
Image-guided radiation therapy assists in improving the precision and accuracy of daily radiation treatments. The location of the tumour can vary from day to day depending on factors such as internal organ movements between treatments and variations in patient’s relative position at the time of treatment. Orthogonal X-ray images and CT scans would be taken prior to each treatment and then compared to the planning CT images. By integrating these images, we are able to adjust the patient’s position accordingly to ensure that the radiation is accurately directed as planned.

Tumours are not perfectly shaped like a box but rather shaped irregularly. With two-dimensional radiation treatments, radiation beams are delivered in straight lines. This means that while the tumour is treated, all of the surrounding healthy tissue is being irradiated as well. When technology advanced, three-dimensional conformal radiation therapy (3DCRT) enables us to conform the high dose to the shape of the tumour, sparing the surrounding healthy tissue. However, 3DCRT is still not perfect. Anatomical structures, such as the nasopharynx, has a special "C shape" which wraps around the spinal cord. Minimal dose to the spinal cord and other surrounding organs such as the parotid glands cannot be achieved using 3DCRT. IMRT is an advanced type of 3DCRT that uses even more sophisticated software (powerful computer planning programs) and hardware (dynamic multi-leaf collimators) to control the shape and intensity of radiation delivered to the desired parts of the treatment area.

How does IMRT work?
Using CT images, the oncologist and radiation therapists visualize the tumour and the surrounding region in three dimensions. The oncologist designates specific doses of radiation that the tumour and surrounding normal tissues should receive. With the help of a powerful computer planning program, the radiation therapist develops an optimal plan to meet the specified requirements. This process is called "inverse treatment planning". The resulting radiation dose distribution is consistent with the shape of the tumour by modulating the intensity of the radiation beam. The ultimate goal of this inverse treatment planning is to maximize tumour dose while simultaneously protecting the surrounding normal tissue.

In addition to the sophisticated computer program, IMRT also involves the use of dynamic multi-leaf collimators located in the radiation treatment machine. They are computer-controlled devices made up of individual "leaves" that can move independently in and out of the radiation beam. They vary the intensity of the radiation beam across the treatment area. With IMRT, the patient is treated with many small beams from many angles, each one of which has a different intensity. The resulting radiation beams are conformed to the shape of the tumour according to the optimal plan generated by the oncologist and radiation therapist. This results in better tumour targeting, lessened side effects and improved treatment outcomes.

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