The need for rotational margins in intensity-modulated radiotherapy and a new method for planning target volume design

Mark Peter Langer, Lech Papiez, Siarhei Spirydovich, Van Thai

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

Purpose: The effect of rotational errors on the coverage of clinical target volumes (CTVs) is examined. A new planning target volume (PTV) construction that considers the individual paths traced by movements of the target boundary points is developed. Methods and Materials: A standard uniform margin expansion was compared with a PTV constructed from the space swept out by a concave moving target. A new method formed the PTV by aggregating the separate convex hulls taken of the positions of the individual target boundary points in a sampling of CTV displacements. Results: A 0.5-cm uniform margin adequate for translations was inadequate given CTV rotation about a fixed off-center axis. A PTV formed of the target's swept-out area was 22% smaller than needed for coverage by a uniform margin, but computationally is not readily extended to translations combined with rotations about a shifting axis. Forming instead the union of convex hulls of the boundary points in a sampling of CTV displacements represented these movements in the PTV design and retained the target's concave shape. Conclusions: Planning target volumes should accommodate target rotation. The union of convex hulls of the boundary point positions in a sampling of displacements can effectively represent multiple sources of deviations while preserving target concavities.

Original languageEnglish (US)
Pages (from-to)1592-1603
Number of pages12
JournalInternational Journal of Radiation Oncology Biology Physics
Volume63
Issue number5
DOIs
StatePublished - Dec 1 2005

Keywords

  • Concavities
  • IMRT
  • Margins
  • Target design

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation

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