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IMRT – Intensity Modulated Radio Therapy

Intensity-modulated radiation therapy (IMRT) is an advanced mode of high-precision radiotherapy that utilizes 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 to regions within the tumor while minimizing the dose to surrounding normal critical structures. Treatment is carefully planned by using 3-D computed tomography (CT) 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 several intensity-modulated fields coming from different beam directions produce a custom tailored 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. IMRT does require longer daily treatment times and delivers a low dose to larger volumes of normal tissue than conventional radiotherapy.

Currently, IMRT is being used most extensively to treat cancers of the prostate, head and neck, and central nervous system. IMRT has also been used in limited situations to treat breast, thyroid, lung, as well as in gastrointestinal, gynecologic malignancies and certain types of sarcomas. IMRT may also be beneficial for treating pediatric malignancies.

Radiation therapy, including IMRT, 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.

IGRT Image Guided Radiotherapy

This is not a new type of radiation, it denotes the ability to visualize the movement of tumors and organs during and in-between treatments. It requires a Linear accelerator capable of delivering 3D conformal radiotherapy or IMRT with the addition of imaging capabilities such as cone beam CT.

It accounts for internal motion of organs due to physiologic processes (breathing, rectum or bladder filling, swallowing, etc.). It reduces the exposure of normal tissues to radiotherapy if there is a decrease in the tumor size or weight loss. This makes it very useful in the treatment of prostate, head and neck, lung, gastro-intestinal and gynecological tumors.

Fiducial markers are frequently utilized for IGRT. Such markers help the Radiation Oncologist target the tumor with high precision since they accurately show the position of the organ or tumor on a daily basis. These markers may need to be placed directly inside the area of treatment.

There are several different types of fiducial markers. They include gold seed markers, coils, electromagnetic beacons that emit radio signals such as the ones used for the Calypso localization systems.

IGRT is currently available at all of the Robert Boissoneault Oncology Institute locations, utilizing Varian Rapid Arc, Calypso, Exac Trac and BAT ultrasound technologies. Not all patients are candidates for IGRT, ask your doctor if this treatment technique would be of benefit to you.

3D Conformal Radiotherapy

This type of treatment started with the introduction of CT scanners and modern treatment planning computers in the mid to late 1980’s. It is delivered by a Linear Accelerator or “LINAC” that delivers a high energy x-ray beam.

It allows for 3-dimensional representation of the organs and multiple beam angles can be used to reduce toxicity to normal tissues.   Radiation Oncologists have the ability to track dose to normal structures using dose volume histograms.

With newer Linear accelerators and treatment planning software the 3D techniques have been refined and this treatment method is widely utilized for different types of tumors. It can be used for many conditions including, brain, head and neck, lung, abdominal, pelvic and skeletal system tumors.

3D Conformal Radiotherapy is currently available at all of the Robert Boissoneault Oncology Institute locations. Not all patients are candidates for this type of treatment so ask your doctor if this technique would be of benefit to you.