title: Effect of spine hardware on small spinal stereotactic radiosurgery dosimetry.
abstract: Monte Carlo (MC) modeling of a 6 MV photon beam was used to study the dose perturbation from a titanium rod 5 mm in diameter in various small fields range from 2 × 2 to 5 × 5 cm(2). The results showed that the rod increased the dose to water by ∼6% at the water-rod interface because of electron backscattering and decreased the dose by ∼7% in the shadow of the rod because of photon attenuation. The Pinnacle(3) treatment planning system calculations matched the MC results at the depths more than 1 cm past the rod when the correct titanium density of 4.5 g cm(-3) was used, but significantly underestimated the backscattering dose at the water-rod interface. A CT-density table with a top density of 1.82 g cm(-3) (cortical bone) is a practical way to reduce the dosimetric error from the artifacts by preventing high density assignment to them, but can underestimates the attenuation by the titanium rod by 6%. However, when multi-beam with intensity modulation is used in actual patient spinal stereotactic radiosurgery treatment, the dosimetric effect of assigning 4.5 instead of 1.82 g cm(-3) to titanium implants is complicated. It ranged from minimal effect to 2% dose difference affecting 15% target volume in the study. When hardware is in the beam path, density override to the titanium hardware is recommended.
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.forename: James N
authors.initials: JN
authors.lastname: Yang
authors.forename: Xiaoqiang
authors.initials: X
authors.lastname: Li
authors.forename: Ramesh
authors.initials: R
authors.lastname: Tailor
authors.forename: Oleg
authors.initials: O
authors.lastname: Vassilliev
authors.forename: Paul
authors.initials: P
authors.lastname: Brown
authors.forename: Laurence
authors.initials: L
authors.lastname: Rhines
authors.forename: Eric
authors.initials: E
authors.lastname: Chang
mesh_terms: D016477:Artifacts; D006801:Humans; D009010:Monte Carlo Method; D011874:Radiometry / Q000379:methods*; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D013131:Spine / Q000000981:diagnostic imaging / Q000601:surgery*; D014025:Titanium; D014057:Tomography, X-Ray Computed; D014867:Water
chemical_list: D014867:Water; D014025:Titanium