Intensity Modulated Radiation Therapy (IMRT) is an advanced form of radiation treatment that allows radiation oncologists to precisely target tumor cells. It is a noninvasive therapy that uses Computed Tomography (CT) or other imaging modalities to build three-dimensional diagnostic images and map treatment plans to deliver tightly focused radiation beams of varying intensity to cancerous tumors without needles, tubes or catheters. Varying the intensity of these beams enhances the ability of IMRT to maximize dosage and minimize the amount of radiation distributed to surrounding healthy tissue.
What is IMRT?
- IMRT involves varying (modulating) the intensity of the radiation being used as therapy for cancer.
- It is an advanced form of 3-D conformal radiation treatment, which is a method of conforming a three-dimensional target plan to a tumor.
- IMRT technology enables doctors to place precisely shaped beams of radiation into tumors, and to control the intensity of the radiation beams throughout the treatment area. Consequently, the dose can be higher in the most aggressive areas of the tumor and lower in areas where the beam is near or passing through healthy tissue or structures.
- Conventional radiation therapy, on the other hand, targets a uniform shape to a total area to cover the tumor. Therefore, some healthy tissue is always irradiated and the target area receives an even dose of radiation across the entire target area.
Why is it used?
- The end result is better tumor control, less damage to healthy tissues and structures in the treatment area, and a better quality of life for the patient.
- Side effects tend to be more manageable.
- IMRT can be used to treat tumors that might have been considered untreatable in the past due to close proximity of vital organs and structures.
- The most commonly treated areas today are: prostate, spine, lung, breast, kidney, pancreatic tumors, liver, larynx, sinus and brain.
How is treatment planned and delivered?
- IMRT begins with an intensive, computerized treatment planning process coordinated by a team of specially trained radiation oncology experts. A radiation oncologist uses 3-D scanning images to draw the shape, size and location of the tumor to be targeted. Then, a radiation physicist devises an individualized treatment plan.
- A specialized computer program optimizes a treatment plan based on a physician’s dose instructions and the 3-D diagnostic images.
- To assist in targeting with more accuracy, the patient is usually fitted with a reusable localization device, such as a mask, body frame, etc.
- During treatment sessions, the high-energy radiation used in IMRT is generated by a linear accelerator. The treatment unit contains a multileaf collimeter consisting of 120 small metal leaves, or rods, that shape the radiation beam and move in and out during treatment. This varies the amount of radiation for each area, blocking radiation out or allowing it in according to the treatment plan.
- The beams may be moved dozens or hundreds of times and each may vary with a different intensity, resulting in radiation sculpted in three dimensions.