Iranian Journal of Medical Physics

Iranian Journal of Medical Physics

Effect of Phantom Size and Tube Voltage on the Size-Conversion Factor for Patient Dose Estimation in Computed Tomography Examinations

Document Type : Technical Notes

Authors
Dwi Adhianto 1
Choirul Anam 1
Heri Sutanto 1
Mohd Hanafi Ali 2
1 Department of Physics, Faculty of Mathematics and Natural Sciences, Diponegoro University, Jl. Prof. Soedarto SH, Tembalang, Semarang 50275, Central Java, Indonesia.
2 Discipline of Medical Imaging Science, Faculty of Health Sciences, The University of Sydney, 75 East St, Lidcombe 2141 NSW, Australia
10.22038/ijmp.2019.43059.1649
Abstract
Introduction: This study aimed to establish the conversion factors to normalize the output dose of volumetric computed tomography dose index (CTDIvol) to the patient dose (i.e. size-specific dose estimate (SSDE)) for various phantom diameters and tube voltages.
Material and Methods: In-house cylindrical acrylic phantoms with physical diameters ranging from 8 to 40 cm were developed in this study. Each phantom had a hole in the center and four holes in the peripheral areas. The phantoms were scanned by a Siemens Somatom Definition AS CT Scanner using different tube voltages (i.e. 80, 100, 120, and 140 kVps) and with 200 mAs and 10 mm slice thickness. In addition, the doses in every hole and phantom were measured using a Raysafe X2 CT Sensor. The weighted SSDE (SSDEw) values were calculated using the five holes in every measurement. The size-conversion factors for the body and the head CTDI phantoms were established by dividing the SSDEw for various sizes with the SSDEw at the water-equivalent diameter of 33.90 cm and 16.95 cm, respectively.
Results: The results revealed that the size-conversion factor exponentially decreased with an increase in the phantom size. It was also found that the size-conversion factor was affected by the tube voltages. Furthermore, the different size-conversion factor between 80 and 140 kVp was more than 15% in very thin and obese patients.
Conclusion: Higher accuracy of the size-specific dose estimation can be achieved considering the impact of the tube voltages beside the size of the patient.
Keywords
X
ray Computed Tomography Patient Dose Radiation Dosimetry Radiation Dosage
Subjects

  1.  

     

    1. Kalender WA. X-ray computed tomography. Physics in Medicine and Biology. 2006; 51: 29–43.
    2. Seeram E. Computed tomography: Physical principles and recent technical advances. Journal of Medical Imaging and Radiation Sciences. 2010; 41: 87-109.
    3. Martin CJ. Management of patient dose in radiology in the UK. Radiation Protection Dosimetry. 2011; 147: 355–72.
    4. Le Coultre R, Bize J, Champendal M, Wittwer D, Ryckx N, Aroua A, Trueb P, Verdun FR. Exposure of the Swiss population by radiodiagnostics: 2013 review. Radiation protection dosimetry. 2016;169(1-4):221-4.
    5. Parry RA, Glaze SA, Archer BR. Typical patient radiation doses in diagnostic radiology. RadioGraphics. 1999; 19: 1289–302.
    6. Anam C, Fujibuchi T, Haryanto F, Widita R, Arif I, Dougherty G. An evaluation of computed tomography dose index measurements using a pencil ionisation chamber and small detectors. Journal of Radiological Protection. 2019; 39: 112–24.
    7. Figueira C, Di Maria S, Baptista M, Mendes M, Madeira P, Vaz P. Paediatric CT exposures: comparison between CTDIVOL and SSDE methods using measurements and Monte Carlo simulations. Radiation Protection Dosimetry. 2015; 165: 210-5.
    8. Bashier EH, Suliman II. Multi‑slice CT examinations of adult patients at Sudanese hospitals: Radiation exposure based on size‑specific dose estimates (SSDE). La Radiologia Medica. 2018; 123: 424–31.
    9. AAPM. Size-specific dose estimates (SSDE) in pediatric and adult body CT examinations. AAPM Report no 204. 2011.
    10. Anam C, Haryanto F, Widita R, Arief I. Automated estimation of patient’s size from 3D image of patient for size specific dose estimate. Advanced Science, Engineering and Medicine. 2015; 7: 892-6.
    11. Anam C, Haryanto F, Widita R, Arief I, Dougherty G. Automated calculation of water-equivalent diameter (DW) based on AAPM task group 220. Journal of Applied Clinical Medical Physics. 2016; 17: 320-33.
    12. Anam C, Haryanto F, Widita R, Arif I, Dougherty G, McLean D. Volume computed tomography dose index (CTDIvol) and size-specific dose estimate (SSDE) for tube current modulation (TCM) in CT scanning. International Journal of Radiation Research. 2018; 16: 289-97.
    13. Gao Y, Quinn B, Pandit-Taska N, Behr G, Mahmood U, Long D, et al. Patient-specific organ and effective dose estimates in pediatric oncology computed tomography. Physica Medica. 2018; 45: 146–55.
    14. Abuhaimed A, Martin CJ, Demirkaya O. Influence of cone beam CT (CBCT) scan parameters on size specific dose estimate (SSDE): A Monte Carlo study. Physics in Medicine and Biology. 2019; 64: 115002.
    15. Nasir M, Pratama D, Anam C, Haryanto F. Calculation of size specific dose estimates (SSDE) value at cylindrical phantom from CBCT Varian OBI v1.4 X-ray tube EGSnrc Monte Carlo simulation based. Journal of Physics: Conference Series. 2016; 694: 012040.
    16. Haba T, Koyama S, Kinomura Y, Ida Y, Kobayashi M. Influence of 320-detector-row volume scanning and AAPM report 111 CT dosimetry metrics on size-specific dose estimate: a Monte Carlo study.  Australasian Physical & Engineering Sciences in Medicine. 2016; 39: 697–703.
    17. Andriani I, Budi WS, Sutanto H, Anam C. Analysis of the effect of phantom CT scan diameter variations on radiation dose with IndoseCT. International Journal of Allied Medical Sciences and Clinical Research. 2017; 7: 21-7.
    18. Hossain A, Saha SK. Polymethyl Methacrylate phantom on CT imaging to evaluate size-specific effective dose in pediatric and adult body. International Journal of Biomedical Science and Engineering. 2015; 3: 82-8.
    19. Kamezawa H, Arimura H, Arakawa H, Kameda N. Investigation of a practical patient dose index for assessment of patient organ dose from cone-beam computed tomography in radiation therapy using a Monte Carlo simulation. Radiation Protection Dosimetry. 2018; 181: 333-42.
    20. Anam C, Arif I, Haryanto F, Widita R, Lestari FP, Adi K, et al. A simplified method for the water-equivalent diameter calculation to estimate patient dose in CT examinations. Radiation Protection Dosimetry. 2019; 185: 42-9.
    21. Menke J. Comparison of different body size parameters for individual dose adaptation in body CT of adults. Radiology 2005; 236: 565–71.
    22. Schindera ST, Nelson RC, Toth TL, Nguyen GT, Toncheva GI, DeLong DM, et al. Effect of patient size on radiation dose for abdominal MDCT with automatic tube current modulation: Phantom study. American Journal of Roentgenology. 2008; 190: 100–5.
    23. Anam C, Fujibuchi T, Toyoda T, Sato N, Haryanto F, Widita R, et al. A simple method for calibrating pixel values of the CT localizer radiograph for calculating water-equivalent diameter and size-specific dose estimate. Radiation Protection Dosimetry. 2018; 179: 158–68.
    24. Li X, Yang K, Liu B. A study of the midpoint dose to CTDIvol ratio: Implications for CT dose evaluation. Medical Physics. 2016; 43(11): 5878-88.

     

Iranian Journal of Medical Physics
Volume 17, Issue 5
September and October 2020
Pages 282-288

  • Receive Date 09 September 2019
  • Revise Date 19 October 2019
  • Accept Date 06 November 2019