Quantification of the impact of MLC modeling and tissue heterogeneities on dynamic IMRT dose calculations

I. B. Mihaylov, F. A. Lerma, M. Fatyga, J. V. Siebers

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


This study quantifies the dose prediction errors (DPEs) in dynamic IMRT dose calculations resulting from (a) use of an intensity matrix to estimate the multi-leaf collimator (MLC) modulated photon fluence (DPEIGfluence) instead of an explicit MLC particle transport, and (b) handling of tissue heterogeneities (DPEhetero) by superposition/convolution (SC) and pencil beam (PB) dose calculation algorithms. Monte Carlo (MC) computed doses are used as reference standards. Eighteen head-and-neck dynamic MLC IMRT treatment plans are investigated. DPEs are evaluated via comparing the dose received by 98% of the GTV (GTV D98%), the CTV D95%, the nodal D90%, the cord and the brainstem D02%, the parotid D50%, the parotid mean dose (DMean), and generalized equivalent uniform doses (gEUDs) for the above structures. For the MC-generated intensity grids, DPEIGfluence is within ±2.1% for all targets and critical structures. The SC algorithm DPEhetero is within ±3% for 98.3% of the indices tallied, and within ±3.4% for all of the tallied indices. The PB algorithm DPEhetero is within ±3% for 92% of the tallied indices. Statistical equivalence tests indicate that PB DPEhetero requires a ±3.6% interval to state equivalence with the MC standard, while the intervals are <1.5% for SC DPEhetero and DPEIGfluence. Overall, these results indicate that SC and MC IMRT dose calculations which use MC-derived intensity matrices for fluence prediction do not introduce significant dose errors compared with full Monte Carlo dose computations; however, PB algorithms may result in clinically significant dose deviations.

Original languageEnglish (US)
Pages (from-to)1244-1252
Number of pages9
JournalMedical physics
Issue number4
StatePublished - 2007
Externally publishedYes


  • Dose computation
  • Fluence
  • IMRT
  • MLC
  • Monte Carlo
  • Tissue heterogeneities

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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