FRONTLINE

Beam-Shaping Device On Target

 

If one word could best describe a new device that can treat small, irregular-shaped brain tumors, it would have to be innovative.

 

The computer-controlled miniature multileaf collimator (MMLC), developed and patented in the Department of Radiation Physics at M. D. Anderson, is the latest weapon in stereotactic radiotherapy and radiosurgery.

 

Using a miniature multileaf collimator, Dr. Almon S. Shiu (left) and Dr. Lei Dong are able to more precisely conform the radiation dose delivered to small tumors of virtually any shape while avoiding damage to nearby normal tissue.

The MMLC's ability to shape individual treatment fields to fit the precise dimensions of a well-defined target specified by the radiation oncologist and neurosurgeon is its greatest asset.

 

"It allows us to conform the radiation dose delivered to tumors of virtually any shape while avoiding nearby normal tissue and critical structures such as the optic nerves and optic chiasm," says Dr. Almon S. Shiu, assistant professor of radiation physics. "With conventional linear-accelerator circular collimators, the treatment of non-spherical tumors affects a larger proportion of healthy brain."

 

There are several advantages to the MMLC, including:

 

· Decreased brain toxicity.

 

· Finer resolution. The MMLC uses four millimeters of resolution versus 10mm for traditional multileaf collimators. "The former resolution is better for irradiating small, irregular malignancies, particularly those that lie close to sensitive areas in or near the brain," says Dr. Kenneth R. Hogstrom, chairman of the Department of Radiation Physics.

 

· Greater flexibility in altering the pattern of beam delivery.

 

· Improved field shaping capabilities, allowing conformal therapy to both convex and concave targets.

 

· Use of a single isocenter (point in patient to which all radiation beams are focused) to deliver treatment fields. To conform to a non-spherical tumor using standard technology, two or more overlapped spherical treatment volumes, each having its own isocenter, are needed.

 

"This leads to hot areas within the overlap region and a high brain dose, which increases the likelihood for complications," Dr. Shiu explains. "Therefore, an MMLC approach is most desirable."

 

Radiation oncologist Dr. Moshe H. Maor, Dr. Shiu and their team are enrolling patients to test a prototype of the MMLC, with two patients having received treatment thus far.

 

Through a licensing agreement between M. D. Anderson and Radionics Software Applications, Inc., a commercial MMLC based on the cancer center's design is currently being manufactured and is expected to be available late fall.

 

The Radionics version will have a larger field size, expanding the treatment areas to the prostate and head and neck.

 

Through the ingenuity of co-inventors Dr. Shiu, James Ewton, Henry Rittichier, Shih-Ming Tung, Jeremy Wong and Dr. Lei Dong, and support from the Texas Higher Education Coordinating Board, the MMLC gives patients one more chance in their fight for a cure.

 

-- Eileen A. Ellig

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