First, they exposed the spinal cords and brains of healthy rats to thicker (0.27 to 0.68 millimeter) microbeams at high doses of radiation and monitored the animals for signs of tissue damage. After seven months, animals exposed to beams as thick as 0.68 millimeter showed no or little damage to the nervous system.
"This demonstrates that the healthy-tissue-sparing nature of the technique stays strong at a beam thickness that is within a range that could be produced by specialized x-ray tubes of extremely high voltage and current," Dilmanian said. Such x-ray sources may become available sometime in the future and may allow the implementation of the method in hospitals.
Next, the scientists demonstrated the ability to "interlace" two parallel arrays of the thicker microbeams at a 90-degree angle to form a solid beam at a small target volume in the rats' brains, and measured the effects of varying doses of radiation on the targeted tissue volume and the surrounding tissue using magnetic resonance imaging (MRI) scans. For interlacing, the gaps between the beams in each array were chosen to be the same as the thickness of each beam, so the beams from one array would fill the gaps in the other to produce the equivalent of an unsegmented beam in the target volume only. "In this way we are effectively delivering an unsegmented broad beam type of dose to just the target region -- which could be a tumor, or a non-tumerous target we want to ablate -- while exposing the surrounding tissue to segmented radiation from which it can recover," Dilmanian said.
The MRI scans showed that at a particular dose of radiation, the new configuration could produce major damage to the target volume but virtually no damage beyond the target range. "The dose of radiation delivered to the target volume would have been enough to ablate a malignant tumor," Dilmanian said.
"These results show that thick microbeams generated by special x-ray tubes
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Contact: Karen McNulty Walsh
kmcnulty@bnl.gov
631-344-8350
DOE/Brookhaven National Laboratory
9-Jun-2006