Iranian Journal of Medical Physics

Iranian Journal of Medical Physics

Evaluation of Effect of Different Computed Tomography Scanning Protocols on Hounsfield Unit and Its Impact on Dose Calculation by Treatment Planning System

Document Type : Original Paper

Authors
Mamta Mahur 1
Om Prakash Gurjar 2
RK GROVER 1
PS Negi 1
Richa Sharma 1
Anshu Singh 1
Munendra Singh 3
1 Department of Radiotherapy, Delhi State Cancer Institute(s), Dilshad Garden, Delhi – 110095, India
2 Roentgen-SAIMS Radiation Oncology Centre, Sri Aurobindo Institute of Medical Sciences
3 Department of Physics, School of Basic Sciences & Research, Sharda University, Greater Noida, Uttar Pradesh – 201306, India
10.22038/ijmp.2017.21942.1207
Abstract
Introduction: In radiotherapy treatment planning system (TPS), basic input is the data from computed tomography (CT) scan, which takes into account the effect of inhomogeneities in dose calculations. Measurement of CT numbers may be affected by scanner-specific parameters. Therefore, it is important to verify the effect of different CT scanning protocols on Hounsfield unit (HU) and its impact on dose calculation. This study was carried out to analyse the effect of different tube voltages on HU for various tissue substitutes in phantom and their dosimetric impact on dose calculation in TPS due to variation in HU–relative electron density (RED) calibration curves.
Materials and Methods: HU for different density materials was obtained from CT images of the phantom acquired at various tube voltages. HU-RED calibration curves were drawn from CT images with various tissue substitutes acquired at different tube voltages used to quantify the error in dose calculation for different algorithms. Doses were calculated on CT images acquired at 120 kVp and by applying CT number to RED curve obtained from 80, 100, 120, and 140 kVp voltages.
Results: No significant variation was observed in HU of different density materials for various kVp values. Doses calculated with applying different HU-RED calibration curves were well within 1%. Conclusion: Variation in doses calculated by algorithms with various HU-RED calibration curves was found to be well within 1%. Therefore, it can be concluded that clinical practice of using the standard HU-RED calibration curve by a 120 kVp CT acquisition technique is viable.
Keywords
Computed Tomography Hounsfield Units
Phantom
Treatment Planning System
Subjects
  1. Watanabe Y. Derivation of linear attenuation coefficients from CT numbers for low energy photons. Phys Med Biol. 1999; 44:2201-11.
  2. Das IJ, Cheng CW, Cao M, Johnstone PAS. Computed tomography imaging parameters for inhomogeneities correction in radiation treatment planning. J Med Phys. 2016;41:3-11. DOI:10.4103/0971-6203.177277.
  3. Roa AMA, Andersen HK, Martinsen AC. CT image quality over time: comparison of image quality for six different CT scanners over a six-year period. J Appl Clin Med Phys. 2015;16: 4972. DOI: 10.1120/jacmp.v16i2.4972.
  4. Constantinou C, Harrington JC, DeWerd LA. An electron density calibration phantom for CT-based treatment planning computers. Med Phys. 1992;19:325–7. DOI: 10.1118/1.596862.
  5. Guan H, Yin FF, Kim JH. Accuracy of inhomogeneity correction in photon radiotherapy from CT scans with different settings. Phys Med Biol. 2002;47:223–31.
  6. Moyers MF, Miller DW, Siebers JV, Galindo R, Sun S, Sardesai S. Water equivalence of various materials for 155 to 250 MeV protons. Med Phys.1992;19: 829.
  7. Nobah A, Moftah B, Tomic N, Devic A. Influence of electron density spatial distribution and x-ray beam quality during CT simulation on dose calculation accuracy. J Appl Clin Med Phys. 2011;12: 3432. DOI: 10.1120/jacmp.v12i3.3432.
  8. Goodenough DJ. Catphan 500 and 600 manual. Greenwich, NY: The Phantom Laboratory; 2012.
  9. Sande EP, Martinsen AC, Hole EO, Olerud HM. Inter phantom and inter scanner variations for Hounsfield units-establishment of reference values for HU in a commercial QA phantom. Phys Med Biol. 2010;55: 5123-35. DOI: 10.1088/0031-9155/55/17/015.
  10. Cozzi L, Fogliata A, Buffa F, Bieri S. Dosimetric impact of computed tomography calibration on a commercial treatment planning system for external radiation therapy. Radiother Oncol. 1998;48: 335–8. DOI: 10.1016/S0167-8140(98)00072-3.
  11. Sharma DS, Sharma SD, Sanu KK, Saju S, Deshpande DD, Kannan S , Performance evaluation of a dedicated computed tomography scanner used for virtual simulation using inhouse fabricated CT phantoms. J Med Phys 2006;31:28–35.
  12. Cropp RJ, Seslija P, Tso D, Thakur Yogesh. Scanner and kVp dependence of measured CT numbers in the ACR CT phantom. J Appl Clin Med Phys 2013;14:4417.
  13. Maria AR, Anderson HK, Martinsen AC. CT image quality over time: comparison of image quality for six different CT scanners over a six-year period.  J Appl Clin Med Phys 2015;16:4972.
  14. Gulliksurd K, Stokke C, Martinsen AC. How to measure CT image quality: Variations in CT-numbers, uniformity and low contrast resolution for a CT quality assurance phantom. Phys Med 2014;30:521-6.

 

 

Iranian Journal of Medical Physics
Volume 14, Issue 3
September and October 2017
Pages 149-154

  • Receive Date 25 February 2017
  • Revise Date 28 April 2017
  • Accept Date 01 May 2017