Colorwash image demonstrating dose modulation for treatment of a canine nasal tumor. Red corresponds to areas of tissue receiving higher doses of radiation.



IMRTintensity-modulated radiation therapyis a is a state-of-the-art cancer treatment method that delivers high doses of radiation directly to cancer cells in a very targeted way, much more precisely than is possible with conventional radiotherapy. 

IMRT involves varying (or modulating) the intensity of the radiation beam, so that the shape of the resulting dose distribution is tightly matched to the shape of the tumor

IMRT enables an oncology team to direct and narrowly concentrate potent doses of high-energy X rays at a patients tumor while minimizing complications to surrounding healthy tissue.


IMRT targets a tumor with intensity-modulated beams delivered from multiple angles.  The area where the radiation beams intersect creates a finely sculpted radiation cloud that envelops and has the same shape as the tumor.

The IMRT process starts with diagnostic images, for example, computed tomography (CT), magnetic resonance (MR) and/or positron emission tomography (PET) images, of the patients tumor and surrounding anatomy.  These are converted into a custom three-dimensional model of the patients internal anatomy.  A powerful computer program creates a treatment plan based on tumor size, shape, and location within the body, along with the doctors dose prescription.

3-Dimensional model of a patient's nasal tumor, reconstructed using CT images and computer software.

A medical linear accelerator, equipped with a special beam-shaping device called a multileaf collimator (or MLC), delivers the radiation in accordance with the treatment plan.  Varians high-resolution MLC has 120 tungsten metal leaves or slats for shaping the radiation beam to deliver unique doses to very small areasas small as the tip of a pencil.

The linear accelerator rotates around the patient to send beams from multiple angles in order to give the tumor a high dose of radiation while preserving important healthy tissues.  A powerful computer program guides the movement of the Clinac and the MLC to precisely match the treatment plan, delivering the correct dose directly to the target.



LEFT: Multi-leaf collimation. Each leaf moves independently, shaping the radiation beam to the tumor shape. RIGHT: click on this image for a video schematic of how MLC works. MOVIE.wmv


Higher doses of radiation can be delivered directly to tumors and cancer cells, while surrounding organs and tissues are protected.

Lower doses to healthy normal tissues means fewer complications or side effects.  For example, in the case of head and neck tumors, IMRT allows radiation to be delivered in a way that minimizes exposure of the spinal cord, optic nerve, salivary glands or other important structures.  In the case of prostate cancer, exposure of the nearby bladder or rectum can be minimized.

The level of normal tissue sparing achieved with IMRT is dramatic. Clinical experience shows a tremendous reduction in the side effects of radiotherapy when IMRT is used.

Clinicians can treat cancers that were previously untreatable with radiation therapy, sparing some patients the invasive techniques of surgery and/or chemotherapy.

IMRT targets the tumor and not the entire body.

Our desire is for patients to go through treatment without severe side effects.


Varians IMRT combines superior technology with an efficient, reliable process based on integration.

For each step in the IMRT process, Varians IMRT solution has the essential components to support all types of IMRT delivery: segmental IMRT, dynamic IMRT, dynamic conformal arc and electronic compensation.

Varians IMRT offers very high-resolution delivery, giving clinicians the ability to conform the dose tightly to a small or irregularly shaped target. This is especially important when working around small or oddly shaped structures such as the optic nerves or salivary glands. In cases like these, high resolution IMRT can more effectively shape the dose around critical structures.

IMRT helps clinics deliver a powerful beam to a target volume with great precision, allowing veterinarians to prescribe higher doses in order to target tumors with more radiation while sparing healthy surrounding tissue.

Because of the efficiency of Varians complete IMRT system, these treatments can take place within an ordinary radiotherapy treatment timeslot.  This means clinics can deliver more effective treatments in the same amount of time.

A dose volume histogram demonstrating the vast difference between the dose of radiation administered to the tumor and the dose administered to the normal tissue structures.



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Updated: May 12, 2008