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IMRT vs. IGRT

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Prostate Cancer
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Posted 1/9/2010 1:31 AM (GMT 0)
What is the difference between these two modalities.

Are there specific circumstances that suggest one vs the other (assuming radiation is the desired treatment, say for salvage purposes)?

Mel

Posted 1/9/2010 4:03 AM (GMT 0)
Hi Mel,

IMRT is an acronym for Intensity Modulated Radiation Therapy. IGRT is an acronym for Image Guided Radio Therapy. One is an adjunct to the other. The IMRT regulates the collimeters that shape the dose of radiation to the prostate. The IGRT is used to locate the prostate from treatment to treatment and keep the radiation beam aimed at the prostate during each session. There are three gold seeds called "fiduciaries" that are implanted prior to treatment using ultrasound. The seeds are the targets for the IGRT. Google Varian radiation technology and you will get a good crash course in the method and mechanics.

Don
Posted 1/9/2010 4:30 AM (GMT 0)
Don,

Great explanation. I would like to add one piece. Not all treatments of IG/IMRT use the makers.

I did not have any markers implanted before I began my therapy. MD Anderson Orlando utilizes the TOMO (for tomography) HI-ART machine.

I had two CT scans done in my preparation for the treatment. They then placed tattoos on each hip and 1 on my abdomen. Each time I go for treatment, I lie down on the table and am aligned with the tattoos and laser beams to insure that I am level hip and center line. Then the table slides through the device and a CT scan is done. It is compared by software to the originals that were used for targeting. The software makes any minor adjustments for delivery of the beamlets with any internals changes of my body due to full bladder, full bowels, etc.

A second trip through the machine delivers the radiation. In all the entire process takes about 14 minutes per treatment.

It is really petty cool stuff.

Sonny
Posted 1/9/2010 3:13 PM (GMT 0)
And mine was non-TOMO IMRT. It took 7 tattoo on me. They had constant alignment problems, each treatment took from 20-55 minutes.
What Sonny had sounds way more efficient. I was under the Novalis machine, and it used 2 snap x-ray cameras. Once in place, they took snap pictures, and when the 2 x-rays were overlayed to the original, then they were good to go. Other lasers in the room and motion detectors made sure that I was always in the exact place I needed to be.

And with my method, they did use a body cast, that was moulded to my shape from the hips down. Did involve stripping and wearing a gown each time. But did not have to drink any water/fluids, and nothing was inserted up my back end like some do.

Unlike Sonny's description of one pass for radiation, the Novalis set-up indexes the entire machine around the table in 7 distinct positions, and from each position, radiation is administered.

David in SC
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