Courts can look to the specification of a patent to determine the meaning of an ambiguous claim term like "asymmetry," where the context of the term is not expressly recited in the claim but is described in the specification.

The district court ruled in favor of the alleged infringer, finding the claims of the asserted patent invalid. On appeal, the Federal Circuit reversed based on an erroneous claim construction and remanded for further proceedings.

The technology of the asserted patent was directed to a type of radiation therapy for the treatment of cancer where a radiation-containing balloon is inserted in the body near the tumor. The district court construed the claim term “the radiation source further being asymmetrically located and arranged within the expandable surface to provide predetermined asymmetric isodose curves with respect to the apparatus volume” to require that the radiation source be “located and arranged inside the expandable surface so as not to be concentric with the expandable outer surface.” The district court rejected the patentee’s proposed construction, which limited the claimed asymmetry to asymmetry about the longitudinal axis of the balloon. The district court based its construction on the fact the patent specification did not always refer to asymmetry with respect to the longitudinal axis.

On appeal, the patentee argued that the district court erred by failing to limit the claim terms to situations in which asymmetry is achieved by displacing the radiation source from the longitudinal axis. The Federal Circuit agreed, finding that while the location of the asymmetry of the radiation sources was not explicitly recited in the claim, asymmetry is a relative concept that must be read in view of the specification. In particular, the court pointed to the “summary of the invention” and other parts of the specification, and determined that the patentee clearly contemplated that the asymmetry referred to displacement from the longitudinal axis of the balloon.

A copy of the opinion can be found here.