The implication of non-cyclic intrafractional longitudinal motion in SBRT by TomoTherapy

Wensha Yang, Ray Van Ausdal, Paul Read, James Larner, Stanley H Benedict, Ke Sheng

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)2875-2884
Number of pages10
JournalPhysics in Medicine and Biology
Issue number9
StatePublished - 2009
Externally publishedYes

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology


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