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Medical Physics / Volume 37 / Issue 7 / RADIATION MEASUREMENT PHYSICS

Med. Phys. 37, 3560 (2010); http://dx.doi.org/10.1118/1.3455285 (9 pages)

Determination of multislice computed tomography dose index (CTDI) using optically stimulated luminescence technology

Chun Ruan and William J. Clouse

Department of Radiological Sciences, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104

Eduardo G. Yukihara and Patricia B. R. Gasparian

Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078

Salahuddin Ahmad

Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104

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(Received 1 March 2010; accepted 27 May 2010; revised 26 May 2010; published online 15 June 2010)

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Purpose: The extensive use of multislice computed tomography (MSCT) and the associated increase in patient dose calls for an accurate dose evaluation technique. Optically stimulated luminescence (OSL) dosimetry provides a potential solution to the arising concerns over patient dose. This study was intended to evaluate the feasibility and accuracy of OSL dosimeter systems in the diagnostic CT x-ray beam energy range.
Methods: MSCT dose profiles were measured by irradiating OSL strips placed inside the extended PMMA head and body phantoms at different scan conditions by varying kVp settings (100, 120, and 140 kVp) and collimated beam widths (5, 10, 20, and 40 mm). All scans in this study were performed using a GE Lightspeed VCT scanner in axial mode. The exposed strips were then read out using a custom-made OSL strip reader and corrected with field-specific conversion factors. Based on the corrected OSL dose profile, the CTDI450-OSL and CTDI100-OSL were evaluated. CTDI100-IC was also obtained using a 100 mm long pencil ionization chamber for accuracy verification. CTDI100-efficiency can be further evaluated by calculating the ratio of CTDI100-OSL and CTDI450-OSL, which was compared to results from previous studies as well.
Results: The OSL detectors were found to have good sensitivity and dose response over a wide range of diagnostic CT x-ray beam energy viz. the primary beam and the scatter tail section of the dose profile. The differences between CTDI100 values obtained using the OSL strips and those obtained with 100 mm long pencil ionization chamber were <±5% for all scan conditions, indicating good accuracy of the OSL system. It was also found that the CTDI100-efficiency did not significantly change as the beam width increased and tube voltage changed. The average CTDI100-efficiency at the center of the head and body phantoms were 72.6% and 56.2%, respectively. The corresponding values for the periphery of the head and body phantoms were 85.0% and 81.7%. These results agreed very well with previous results from the literature using other detection techniques or Monte Carlo simulations.
Conclusions: The LED-based OSL system can be an accurate alternative device for CT dose evaluations. CTDI100 measurement with the use of a 100 mm pencil ionization chamber substantially underestimates the CTDI∞ value even with 5 mm collimated beam width. The established complete set of CTDI100-efficiency correction factors for various scan parameters allows for accurately estimating CTDI∞ with the current use of pencil chamber and dose phantoms. Combined with the simple calibration, it gives this work great potential to be used not only in routine clinical quality assurance checks but also as a promising tool for patient organ dose assessment.

© 2010 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

The authors would like to thank Landauer Inc. for the Al2O3:C detector material provided for these investigations and Mike Lucas (Oklahoma State University’s Physics and Chemistry Instrument Shop) for the construction of parts of the OSL strip reader and of the OSL strip holder.

Article Outline

  1. INTRODUCTION
  2. MATERIALS AND METHODS
    1. OSL dosimetry system
    2. OSL dose profile measurement
      1. Dose profile measured at different kVp settings
      2. Dose profile measured at different beam widths
    3. OSL dose profile generation
    4. OSL dose profile verification
    5. CTDI100-efficiency
  3. RESULTS
    1. OSL dose profile
    2. OSL dose profile verification
    3. CTDI100-efficiency
  4. DISCUSSION
  5. CONCLUSIONS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3455285

KEYWORDS and PACS

Keywords

computerised tomography, dosimetry, phantoms, photoluminescence, optically stimulated luminescence (OSL), computed tomography (CT), computed tomography dose index (CTDI), dose profile, radiation dose

PACS

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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Medical Physics is an official science journal of the AAPM and of the COMP/CCPM/IOMP
William R. Hendee, Editor
Departments of Radiology, Radiation Oncology, Biophysics, Community and Public Health, Medical College of Wisconsin
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College Park, Maryland 20740
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