Posts Tagged ‘MLC’
Generation V – Capable of reducing treatment times and enhancing conformality, the next-of-breed IMRT known as VMAT has radiation oncologists beaming.
Imagine a newly diagnosed prostate cancer patient lying on a table in a darkened room, about to undergo intensity-modulated radiation therapy (IMRT). Besides eyeing the linear accelerator anxiously and pondering the side effects radiation might induce (secondary tumors?), he’s also feeling intense pressure to urinate. You made him fill his bladder to lift his reproductive organs out of the way of the beam’s target area-his prostate. But he must ignore that pressure and lie perfectly still. Moving a few millimeters too much could make or break his cure.
Elekta VMAT
In conventional static-field IMRT, that patient must lie prone for five, eight, 10 minutes as you maneuver the linac around him. You deliver a treatment dose; stop and reposition the machine; deliver another dose; stop and reposition the machine; deliver another dose, and so on.
Imagine achieving the same effect in just two or three minutes via the push of a button as your linac rotates around the patient in one or more arcs with the radiation continuously on. As it rotates, the system automatically varies the multileaf collimator (MLC) aperture shape, dose rate, gantry rotation speed and MLC orientation to deliver maximum doses while sparing normal tissue. That’s the promise of volumetric modulated arc therapy (VMAT)-essentially, moving IMRT.
“Instead of covering something from seven angles, you have an infinite number of angles,” says William Bodner, MD, a radiation oncologist at Montefiore Medical Center who has used VMAT since March. “Ten to 15 years ago, we were thinking in terms of static fields and large lead blocks. Now we track these tumors as the machine rotates around, adjusting the shape of the beam. It’s beyond comprehension.”
View the entire article @ http://imaging-radiation-oncology.advanceweb.com/Archives/Article-Archives/Generation-V.aspx
More information can also be found @ http://www.elekta.com/vmat
If you’re looking to find out more on the latest radiotherapy technologies and novel work-in-progress projects, the show floor of the ASTRO Annual Meeting is always a good place to start. This year was no exception, with Swedish equipment vendor Elekta disclosing its latest endeavour to the public for the first time.
To read this article, please continue to :
http://medicalphysicsweb.org/cws/article/research/40925
(sign-in required)
Elekta's 160 leaf MLC - more leaves, less leakage
A linear accelerator produces abeam of either electrons or very high energy X-rays. The radiation beam can be shaped and directed to match the tumor shape. The beam of radiation is directed on to the patient within an accuracy of 2mm. This is achieved by a combination of:
• control and shaping of the X-ray beam
• accurate patient positioning with respect to the X-ray beam.
Shaping of the beam can be achieved in three ways:
• use of the primary and secondary collimators. These are large tungsten blocks which can shape the X-ray beam into the appropriate square shape
• custom blocks – these are cast blocks which are specifically for an individual patient to shield sensitive tissue or structures and can be made to the exact shape
• Multileaf Collimator (MLC) – these are fine leaves (usually1cm wide) that are computer-controlled to match the shape of the tumor. Use of MLC is now common practice in many countries.
MLC Animation
The patient is positioned on a treatment table that can be moved in three linear planes as well as up to two rotational planes.
Treatment Table
The linear accelerator can rotate about the patient allowing the beam to be delivered from several different positions. This results in a higher exposure to the tumor tissue compared to surrounding healthy tissue.
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