Shield for Radiation Therapy Developed in Dental Program at NIST

A dental researcher at the National Institute of Standards and Technology has invented a new shielding material and method for protecting healthy body tissues from radiation during therapy.

The shielding is easy to fabricate and can be used for the treatment of tumors or lesions in the mouth or on the body. It is easily molded and can be altered to fit the contours and configurations required by dentists and radiotherapy technicians.

"The new technique is simpler and less time consuming than current shielding processes," says Frederick E. Eichmiller, inventor and associate director of the American Dental Association Health Foundation Paffenbarger Research Center at NIST.

Fabrication requires only a single appointment for a procedure that is done directly on the patient and, in most cases, can be completed in less than one hour. Eichmiller notes that this is a major improvement over current materials and techniques that require multiple appointments and considerable expertise.

Eichmiller says that he was looking for a way to meet two critical dental requirements. Patients need a shield to protect the salivary glands (important in helping reduce oral decay) that can be destroyed by radiation. Dentists and therapists also need a shielding device that can be made easily in outpatient facilities.

The shields are made from two layers of elastomeric polymers, such as vinyl polysiloxane that is commonly used for dental impressions. It sets to form a rubber-like material. One layer is filled to approximately 95 percent by weight with heavy metal powders of silver, tin or copper that diffuse the radiation.

For external application, the body surface area over the lesion or tumor is outlined with a washable ink. A thin layer of polymer without metal is rolled to the desired thickness like a pie crust and placed on the patient, then molded to anatomical contour. The ink lines transfer to the polymer and serve as a trim guide and for locating the treatment window.

A layer of metal-filled polymer is then rolled to the desired thickness, placed over the unfilled material on the patient, and molded to contour. A dental adhesive applied to the first layer holds the two together. Excess material is removed, and the treatment window is cut through the shield. The required thickness of the polymer layers depends on the power and type of radiation source.

In-mouth shields are fabricated in much the same way as a dental impression. Unfilled material is placed in the patient's mouth and molded to fit the treatment area. The unfilled polymer is covered with a filled layer and then trimmed for patient comfort.

Eichmiller says, "I would not have been able to develop the new shielding method outside of NIST. By working here, I was able to draw upon the expertise of NIST metallurgists, polymer scientists and radiation physicists."

A license to manufacture the new shielding material has been issued by the ADAHF to the L.D. Caulk Division of Dentsply International, in Milford, Del. The Veterans Administration is conducting clinical trials. According to Eichmiller, the product should be on the market in approximately two years.

Support for the project was provided by the National Institute of Dental Research through the Center of Excellence for Materials Science Research at NIST. The center is co-directed by Rafael L. Bowen, director of the ADAHF Paffenbarger Research Center at NIST, and John A. Tesk, leader of the NIST Dental and Medical Materials Group.

As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.