Since the 1990s, researchers have been trying to replace the solid beams used in conventional radiation treatment with parallel arrays of very thin — 25 to 90 μm — planar x-ray beams. High doses of microbeam radiation therapy control malignant tumors in animals with little damage to surrounding tissue; unfortunately, few facilities are equipped with the synchrotrons that can generate thin beams at adequate intensity. As published in PNAS on June 20, researchers at Brookhaven National Laboratory in Upton, N.Y., at Stony Brook University in New York, at the Istituto Neurologico Mediterraneo in Pozzilli, Italy, and at Georgetown University in Washington have reported that they may be able to create the same effect with significantly thicker microbeams by interlacing beams within the target. Because the technology used to form thicker microbeams is more widely available, treatments that employ them may be possible in hospitals of the future. Initially, scientists exposed healthy rats to high doses of radiation using microbeams up to 0.68 mm thick to demonstrate that a thickness within the capability of specialized x-ray tubes has little effect on healthy tissues. In further studies, they found that they could interlace two sets of parallel arrays of thick microbeams at 90° so that the beams of one array would fill the spaces of the opposite array and produce the equivalent of a solid beam in the target only.