title: The implication of non-cyclic intrafractional longitudinal motion in SBRT by TomoTherapy.
abstract: To determine the dosimetric impact of non-cyclic longitudinal intrafractional motion, TomoTherapy plans with different field sizes were interrupted during a phantom delivery, and a displacement between -5 mm and 5 mm was induced prior to the delivery of the completion procedure. The planar dose was measured by film and a cylindrical phantom, and under-dosed or over-dosed volume was observed for either positive or negative displacement. For a 2.5 cm field, there was a 4% deviation for every mm of motion and for a 1 cm field, the deviation was 8% per mm. The dimension of the under/over-dosed area was independent of the motion but dependent on the field size. The results have significant implication in small-field high-dose treatments (i.e. stereotactic body radiation therapy (SBRT)) that deliver doses in only a few fractions. Our studies demonstrate that a small longitudinal motion may cause a dose error that is difficult to compensate; however, dividing a SBRT fraction into smaller passes is helpful to reduce such adverse effects.
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, VA, USA.
authors.forename: Wensha
authors.initials: W
authors.lastname: Yang
authors.forename: Ray
authors.initials: R
authors.lastname: Van Ausdal
authors.forename: Paul
authors.initials: P
authors.lastname: Read
authors.forename: James
authors.initials: J
authors.lastname: Larner
authors.forename: Stan
authors.initials: S
authors.lastname: Benedict
authors.forename: Ke
authors.initials: K
authors.lastname: Sheng
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D009068:Movement; D019047:Phantoms, Imaging; D011874:Radiometry; D016634:Radiosurgery / Q000401:mortality*