IMRT delivery verification using a spiral phantom

Susan L. Richardson, Wolfgang A. Tomé, Nigel P. Orton, Todd R. McNutt, Bhudatt R. Paliwal

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


In this paper we report on the testing and verification of a system for IMRT delivery quality assurance that uses a cylindrical solid water phantom with a spiral trajectory for radiographic film placement. This spiral film technique provides more complete dosimetric verification of the entire IMRT treatment than perpendicular film methods, since it samples a three-dimensional dose subspace rather than using measurements at only one or two depths. As an example, the complete analysis of the predicted and measured spiral films is described for an intracranial IMRT treatment case. The results of this analysis are compared to those of a single field perpendicular film technique that is typically used for IMRT QA. The comparison demonstrates that both methods result in a dosimetric error within a clinical tolerance of 5%, however the spiral phantom QA technique provides a more complete dosimetric verification while being less time consuming. To independently verify the dosimetry obtained with the spiral film, the same IMRT treatment was delivered to a similar phantom in which LiF thermoluminescent dosimeters were arranged along the spiral trajectory. The maximum difference between the predicted and measured TLD data for the 1.8 Gy fraction was 0.06 Gy for a TLD located in a high dose gradient region. This further validates the ability of the spiral phantom QA process to accurately verify delivery of an IMRT plan.

Original languageEnglish (US)
Pages (from-to)2553-2558
Number of pages6
JournalMedical physics
Issue number9
StatePublished - Sep 1 2003
Externally publishedYes


  • IMRT
  • QA phantoms
  • Quality assurence

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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