A method of delivering external radiation beams to a target volume in a body portion includes positioning a radioactive isotope source at a plurality of locations spaced apart around the body portion, and collimating radiation beams of the radioactive isotope source from the plurality of locations, whereby the target volume in the body portion is deposited with a predetermined dose distribution. A radiation device employs a member having a configuration adapted to surround a body portion to be irradiated. The member has a channel and a plurality of collimators spaced apart along and coupled to the channel. The plurality of collimators define a plurality of dwelling locations for a radioactive isotope source in the channel and are configured to collimate radiation beams of the radioactive isotope source.