The implication of non-cyclic intrafractional longitudinal motion in SBRT by TomoTherapy.
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.
Yang
Wensha
W
Department of Radiation Oncology, University of Virginia, Charlottesville, VA, USA.
Van Ausdal
Ray
R
Read
Paul
P
Larner
James
J
Benedict
Stan
S
Sheng
Ke
K
D019583:Dose Fractionation, Radiation; D006801:Humans; D009068:Movement; D019047:Phantoms, Imaging; D011874:Radiometry; D016634:Radiosurgery / Q000401:mortality*