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Utilising pseudo-CT data for dose calculation and plan optimization in adaptive radiotherapy

  • Brendan WhelanEmail author
  • Shivani Kumar
  • Jason Dowling
  • Jarrad Begg
  • Jonathan Lambert
  • Karen Lim
  • Shalini K. Vinod
  • Peter B. Greer
  • Lois Holloway
Scientific Paper

Abstract

To quantify the dose calculation error and resulting optimization uncertainty caused by performing inverse treatment planning on inaccurate electron density data (pseudo-CT) as needed for adaptive radiotherapy and Magnetic Resonance Imaging (MRI) based treatment planning. Planning Computer Tomography (CT) data from 10 cervix cancer patients was used to generate 4 pseudo-CT data sets. Each pseudo-CT was created based on an available method of assigning electron density to an anatomic image. An inversely modulated radiotherapy (IMRT) plan was developed on each planning CT. The dose calculation error caused by each pseudo-CT data set was quantified by comparing the dose calculated each pseudo-CT data set with that calculated on the original planning CT for the same IMRT plan. The optimization uncertainty introduced by the dose calculation error was quantified by re-optimizing the same optimization parameters on each pseudo-CT data set and comparing against the original planning CT. Dose differences were quantified by assessing the Equivalent Uniform Dose (EUD) for targets and relevant organs at risk. Across all pseudo-CT data sets and all organs, the absolute mean dose calculation error was 0.2 Gy, and was within 2 % of the prescription dose in 98.5 % of cases. Then absolute mean optimisation error was 0.3 Gy EUD, indicating that that inverse optimisation is impacted by the dose calculation error. However, the additional uncertainty introduced to plan optimisation is small compared the sources of variation which already exist. Use of inaccurate electron density data for inverse treatment planning results in a dose calculation error, which in turn introduces additional uncertainty into the plan optimization process. In this study, we showed that both of these effects are clinically acceptable for cervix cancer patients using four different pseudo-CT data sets. Dose calculation and inverse optimization on pseudo-CT is feasible for this patient cohort.

Keywords

Electron density MRI treatment planning Adaptive radiotherapy Inverse treatment Planning 

Notes

Acknowledgments

The authors would like to acknowledge Dr Mike Milosevic & Dr Anthony Fyles from Prince Margaret Hospital for supplying the patient CT data used in this study. Brendan Whelan would like to acknowledge The Cancer Institute NSW, Liverpool and Macarthur Cancer Therapy Centres, and the Ingham Institute for scholarship support.

Compliance with ethical standards

Conflicts of interest

None.

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Copyright information

© Australasian College of Physical Scientists and Engineers in Medicine 2015

Authors and Affiliations

  • Brendan Whelan
    • 1
    • 2
    • 3
    Email author
  • Shivani Kumar
    • 1
    • 8
  • Jason Dowling
    • 4
  • Jarrad Begg
    • 1
  • Jonathan Lambert
    • 5
  • Karen Lim
    • 1
    • 8
    • 9
  • Shalini K. Vinod
    • 1
    • 8
    • 9
  • Peter B. Greer
    • 5
    • 6
  • Lois Holloway
    • 1
    • 3
    • 7
    • 8
  1. 1.Liverpool and Macarthur Cancer Therapy Centers and Ingham Institute for Applied Medical ScienceSydneyAustralia
  2. 2.Radiation Physics LaboratoryUniversity of SydneySydneyAustralia
  3. 3.Institute of Medical Physics, School of PhysicsUniversity of SydneySydneyAustralia
  4. 4.Australian e-Health Research CentreCSIRO Computational InformaticsSydneyAustralia
  5. 5.University of NewcastleNewcastleAustralia
  6. 6.Calvary Mater NewcastleNewcastleAustralia
  7. 7.Centre for Medical Radiation PhysicsUniversity of WollongongWollongongAustralia
  8. 8.University of New South WalesSydneyAustralia
  9. 9.University of Western SydneySydneyAustralia

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