title: Interlaced x-ray microplanar beams: a radiosurgery approach with clinical potential.
abstract: Studies have shown that x-rays delivered as arrays of parallel microplanar beams (microbeams), 25- to 90-microm thick and spaced 100-300 microm on-center, respectively, spare normal tissues including the central nervous system (CNS) and preferentially damage tumors. However, such thin microbeams can only be produced by synchrotron sources and have other practical limitations to clinical implementation. To approach this problem, we first studied CNS tolerance to much thicker beams. Three of four rats whose spinal cords were exposed transaxially to four 400-Gy, 0.68-mm microbeams, spaced 4 mm, and all four rats irradiated to their brains with large, 170-Gy arrays of such beams spaced 1.36 mm, all observed for 7 months, showed no paralysis or behavioral changes. We then used an interlacing geometry in which two such arrays at a 90-degree angle produced the equivalent of a contiguous beam in the target volume only. By using this approach, we produced 90-, 120-, and 150-Gy 3.4 x 3.4 x 3.4 mm(3) exposures in the rat brain. MRIs performed 6 months later revealed focal damage within the target volume at the 120- and 150-Gy doses but no apparent damage elsewhere at 120 Gy. Monte Carlo calculations indicated a 30-microm dose falloff (80-20%) at the edge of the target, which is much less than the 2- to 5-mm value for conventional radiotherapy and radiosurgery. These findings strongly suggest potential application of interlaced microbeams to treat tumors or to ablate nontumorous abnormalities with minimal damage to surrounding normal tissue.
authors.affiliation: Medical Department, National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973, USA. dilmanian@bnl.gov
authors.forename: F Avraham
authors.initials: FA
authors.lastname: Dilmanian
authors.forename: Zhong
authors.initials: Z
authors.lastname: Zhong
authors.forename: Tigran
authors.initials: T
authors.lastname: Bacarian
authors.forename: Helene
authors.initials: H
authors.lastname: Benveniste
authors.forename: Pantaleo
authors.initials: P
authors.lastname: Romanelli
authors.forename: Ruiliang
authors.initials: R
authors.lastname: Wang
authors.forename: Jeremy
authors.initials: J
authors.lastname: Welwart
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yuasa
authors.forename: Eliot M
authors.initials: EM
authors.lastname: Rosen
authors.forename: David J
authors.initials: DJ
authors.lastname: Anschel
mesh_terms: D000818:Animals; D001921:Brain / Q000601:surgery; D008279:Magnetic Resonance Imaging; D016634:Radiosurgery / Q000379:methods*; D051381:Rats; D013116:Spinal Cord / Q000601:surgery; D014965:X-Rays