A numerical investigation for the optimal positions and weighting coefficients of point dose measurements in the weighted CTDI

Jang Hwan Choi, Dragos Constantin, Rebecca Fahrig

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

2 Scopus citations


The mean dose over the central phantom plane (i.e., z = 0, dose maximum image) is useful in that it allows us to compare radiation dose levels across different CT scanners and acquisition protocols. The mean dose from a conventional CT scan with table translation is typically estimated by weighted CTDI (CTDIW). However, conventional CTDIW has inconsistent performance, depending on its weighting coefficients («1/2 and 1/2» or «1/3 and 2/3») and acquisition protocols. We used a Monte Carlo (MC) model based on Geant4 (GEometry ANd Tracking) to generate dose profiles in the central plane of the CTDI phantom. MC simulations were carried out for three different sizes of z-collimator and different tube voltages (80, 100, or 120 kVp), a tube current of 80 mA, and an exposure time of 25 ms. We derived optimal weighting coefficients by taking the integral of the radial dose profiles. The first-order linear equation and the quadratic equation were used to fit the dose profiles along the radial direction perpendicular to the central plane, and the fitted profiles were revolved about the Z-axis to compute the mean dose (i.e., total volume under the fitted profiles/the central plane area). The integral computed using the linear equation resulted in the same equation as conventional CTDIW, and the integral computed using the quadratic equation resulted in a new CTDIW (CTDIM W) that incorporates different weightings («2/3 and 1/3») and the middle dose point instead of the central dose point. Compared to the results of MC simulations, our new CTDIM W showed less error than the previous CTDIW methods by successfully incorporating the curvature of the dose profiles regardless of acquisition protocols. Our new CTDIM W will also be applicable to the AAPM-ICRU phantom, which has a middle dose point.

Original languageEnglish
Title of host publicationMedical Imaging 2015
Subtitle of host publicationPhysics of Medical Imaging
EditorsChristoph Hoeschen, Despina Kontos, Christoph Hoeschen
ISBN (Electronic)9781628415025
StatePublished - 2015
EventMedical Imaging 2015: Physics of Medical Imaging - Orlando, United States
Duration: 22 Feb 201525 Feb 2015

Publication series

NameProgress in Biomedical Optics and Imaging - Proceedings of SPIE
ISSN (Print)1605-7422


ConferenceMedical Imaging 2015: Physics of Medical Imaging
Country/TerritoryUnited States

Bibliographical note

Publisher Copyright:
© 2015 SPIE.


  • AAPM-ICRU phantom
  • CT dose index
  • Cone-beam CT
  • Dosimetry
  • Monte Carlo
  • Weighted CTDI


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