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Use of calculations to validate beam quality and relative dose measurements for a kilovoltage X-ray therapy unit

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Abstract

Relative dosimetry measurements are required to fully commission kilovoltage X-ray units for superficial and orthovoltage X-ray therapy. Validation of these relative dosimetry measurements with Monte Carlo methods is advantageous being independent of the measurement process. In this study use is made of the X-ray spectrum generating program SpekPy along with the EGSnrc Monte Carlo code to calculate depth doses and explore the dosimetry effect of changes in backscatter. These calculations are compared with previously reported measurements for the Pantak SXT 150 X-ray therapy unit. SpekPy can also be used to generate half value layer (HVL) values and these are also compared to previously reported HVL measurements for the same X-ray therapy unit. It was found that agreements of the order of 5% in HVL, 3% in depth dose and 1% in backscatter doses were found between Monte Carlo calculations and the previously published measured data. Exit doses in conditions of lack of full backscatter were explored with Monte Carlo calculations demonstrating reduced exit dose up to 20% in these conditions. It is concluded that SpekPy with Monte Carlo codes such as EGSnrc provides a straightforward approach to validating various relative dosimetry measurements in kilovoltage X-ray dosimetry.

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Fig. 1
Fig. 2

Measured data are from a Scalchi et al. [16], b Healy et al. [11], c Natto [14], and d Jurado et al. [13]. SSD and field diameter are as given in Table 2

Fig. 3
Fig. 4

Measured data taken from Healy et al. [11]. In all cases the SSD is 15 cm and the field diameter is 5 cm

Fig. 5

taken from Healy et al. [12] and Monte Carlo (MC) calculations (this work). The SSD is 15 cm the field diameter is 5 cm, with 1 cm of water backscatter thickness. For underlying lead, the thickness of lead is 1 mm for all beam energies except 150 kV where there is 2 mm of lead. Thickness of ICRP cortical bone is 1 cm. Included is data for underlying air from Klevenhagen [24] and Subiel et al. [25]

Fig. 6

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References

  1. International Atomic Energy Agency (2000) Absorbed dose determination in external beam radiotherapy: An international code of practice based on standards of absorbed dose to water, Technical Reports Series No. 398. IAEA, Vienna

  2. Ma C-M, Coffey CW, DeWerd LA, Liu C, Nath R, Setzer SM, Seuntjens JP (2001) AAPM protocol for 40–300 kV x-ray beam dosimetry in radiotherapy and radiobiology. Med Phys 28:868–893. https://doi.org/10.1118/1.1374247

    Article  CAS  PubMed  Google Scholar 

  3. Hill R, Healy B, Holloway L, Kuncic Z, Thwaites D, Baldock C (2014) Advances in kilovoltage x-ray beam dosimetry. Phys Med Biol 59:R183–R231. https://doi.org/10.1088/0031-9155/59/6/R183

    Article  PubMed  Google Scholar 

  4. Hill R, Healy B, Butler D, Odgers D, Gill S, Lye J, Gorjiara T, Pope D, Hill B (2018) Australasian recommendations for quality assurance in kilovoltage radiation therapy from the Kilovoltage Dosimetry Working Group of the Australasian College of Physical Scientists and Engineers in Medicine. Australas Phys Eng Sci Med 41:781–808. https://doi.org/10.1007/s13246-018-0692-1

    Article  PubMed  Google Scholar 

  5. Poludniowski G, Landry G, DeBlois F, Evans P, Verhaegen F (2009) SpekCalc: a program to calculate photon spectra from tungsten anode x-ray tubes. Phys Med Biol 54:N433–N438. https://doi.org/10.1088/0031-9155/54/19/N01

    Article  CAS  PubMed  Google Scholar 

  6. Poludniowski G, Omar A, Bujila R, Andreo P (2021) SpekPy v2.0—a software tool for modelling x-ray tube spectra. Med Phys 48:3630–3637. https://doi.org/10.1002/mp.14945

    Article  PubMed  Google Scholar 

  7. Bujila R, Omar A, Poludniowski G (2020) A validation of SpekPy: a software toolkit for modelling X-ray tube spectra. Phys Med 75:44–54. https://doi.org/10.1016/j.ejmp.2020.04.026

    Article  PubMed  Google Scholar 

  8. Andreo P (2018) Monte Carlo simulations in radiotherapy dosimetry. Radia Oncol 13:121. https://doi.org/10.1186/s13014-018-1065-3

    Article  CAS  Google Scholar 

  9. Kawrakow I (2000) Accurate condensed history Monte Carlo simulation of electron transport. I. EGSnrc, the new EGS4 version. Med Phys 27:485–498. https://doi.org/10.1118/1.598917

    Article  CAS  PubMed  Google Scholar 

  10. Kawrakow I (2000) Accurate condensed history Monte Carlo simulation of electron transport. II. Application to ion chamber response simulations. Med Phys 27:499–513. https://doi.org/10.1118/1.598918

    Article  CAS  PubMed  Google Scholar 

  11. Healy BJ, Gibbs A, Murry RL, Prunster JE, Nitschke KN (2005) Output factor measurements for a kilovoltage x-ray therapy unit. Australas Phys Eng Sci Med 28:115–121. https://doi.org/10.1007/BF03178702

    Article  CAS  PubMed  Google Scholar 

  12. Healy BJ, Sylvander S, Nitschke KN (2009) Dose reduction from loss of backscatter in superficial x-ray radiation therapy with the Pantak SXT 150 unit. Australas Phys Eng Sci Med 31:49–55. https://doi.org/10.1007/BF03178453

    Article  Google Scholar 

  13. Jurado D, Eudaldo T, Carrasco P, Jornat N, Ruiz A, Ribas M (2005) Pantak Therapax SXT 150: performance assessment and dose determination using IAEA TRS 398. Br J Radiol 78:721–732. https://doi.org/10.1259/bjr/15782649

    Article  CAS  PubMed  Google Scholar 

  14. Natto SS (2002) Performance characteristics of the Pantak Therapax-150 superficial X-ray treatment machine: measurements and calculations. Australas Phys Eng Sci Med 25:162–167. https://doi.org/10.1007/BF03178289

    Article  CAS  PubMed  Google Scholar 

  15. Baines J, Sim L (2014) The variation of HVL with focal spot to chamber distance as a function of beam quality for the Pantak Therapax 150 x-ray unit and the implications on dose to water determination using the IPEMB code of practice. Australas Phys Eng Sci Med 37:559–566. https://doi.org/10.1007/s13246-014-0289-2

    Article  PubMed  Google Scholar 

  16. Scalchi P, Avossa C, Hill R, Francescon P, Piermattei A (2016) Advances in kilovoltage x-ray beam dosimetry by Monte Carlo calculations and multiple detector intercomparison. Phys Med 32(Suppl. 1):e60–e61

    Article  Google Scholar 

  17. Kawrakow I, Rogers D, Mainegra-Hing E, Tessier F, Townson R, Walters B (2000) EGSnrc toolkit for Monte Carlo simulation of ionizing radiation transport. https://doi.org/10.4224/40001303

  18. Rogers D, Kawrakow I, Seuntjens J, Walters B, Mainegra-Hing E (2021) NRC user codes for EGSnrc, NRCC report PIRS-702 (RevC). National Research Council Canada, Ottawa

    Google Scholar 

  19. Lye J, Butler D, Webb D (2010) Monte Carlo correction factors for the ARPANSA kilovoltage free-air chambers and the effect of moving the limiting aperture. Metrologia 47:11–20. https://doi.org/10.1088/0026-1394/47/1/002

    Article  Google Scholar 

  20. Kim J, Hill R, Claridge Mackonis E, Kuncic Z (2010) An investigation of backscatter factors for kilovoltage x-rays: a comparison between Monte Carlo simulations and Gafchromic EBT measurements. Phys Med Biol 55:783–797. https://doi.org/10.1088/0031-9155/55/3/016

    Article  CAS  PubMed  Google Scholar 

  21. Baines J, Zawlodzka S, Markwell T, Chan M (2018) Measured and Monte Carlo simulated surface dose reduction for superficial X-rays incident on tissue with underlying air or bone. Med Phys 45:926–933. https://doi.org/10.1002/mp.12725

    Article  CAS  PubMed  Google Scholar 

  22. Butson M, Cheung T, Yu P (2008) Measurement of dose reductions for superficial x-rays backscattered from bone interfaces. Phys Med Biol 53:N329–N336. https://doi.org/10.1088/0031-9155/53/17/N0

    Article  PubMed  Google Scholar 

  23. Hill R, Holloway L, Baldock C (2005) A dosimetric evaluation of water equivalent phantoms for kilovoltage x-ray beams. Phys Med Biol 50:N331–N344. https://doi.org/10.1088/0031-9155/50/21/N06

    Article  CAS  PubMed  Google Scholar 

  24. Klevenhagen S (1982) The build-up of backscatter in the energy range 1 mm Al to 8 mm Al HVT. Phys Med Biol 27:1035–1043. https://doi.org/10.1088/0031-9155/27/8/005

    Article  CAS  Google Scholar 

  25. Subiel A, Silvestre Patallo I, Palmans H, Barry M, Tulk A et al (2020) The influence of lack of reference conditions on dosimetry in pre-clinical radiotherapy with medium energy x-ray beams. Phys Med Biol 65:085016. https://doi.org/10.1088/1361-6560/ab7b30

    Article  CAS  PubMed  Google Scholar 

  26. Mainegra-Hing E, Kawrakow I (2006) Efficient x-ray tube simulations. Med Phys 33:2683–2690. https://doi.org/10.1118/1.2219331

    Article  PubMed  Google Scholar 

  27. Grosswendt B (1990) Dependence of the photon backscatter factor for water on source-to-phantom distance and irradiation field size. Phys Med Biol 35:1233–1245. https://doi.org/10.1088/0031-9155/35/9/004

    Article  Google Scholar 

  28. Andreo P (2019) Data for the dosimetry of low- and medium-energy kV x rays. Phys Med Biol 64:205019. https://doi.org/10.1088/1361-6560/ab421d

    Article  CAS  PubMed  Google Scholar 

  29. British Institute of Radiology and the Institution of Physics and Engineering in Medicine and Biology (1996) Central Axis Depth Dose Data for Use in Radiotherapy: 1996, British Journal of Radiology Supplement 25. British Institute of Radiology, London

    Google Scholar 

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Acknowledgements

Thanks to Paolo Scalchi (Integrated University Health Authority of Udine, Italy) for providing his depth dose measurements in the form of MS Excel spreadsheets.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Author information

Authors and Affiliations

  1. Icon Group, Brisbane, QLD, Australia

    B. J. Healy

  2. Chris O’Brien Lifehouse, Sydney, NSW, Australia

    R. F. Hill

  3. Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia

    R. F. Hill

  4. Biomedical Innovation, Chris O′Brien Lifehouse, Sydney, NSW, Australia

    R. F. Hill

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  1. B. J. Healy
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Contributions

All authors contributed to the study conception and design. Data collection and analysis was performed by BH. The first draft of the manuscript was written by BH and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to B. J. Healy.

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Appendix

Appendix

This appendix provides practical information on how to utilize SpekPy and EGSnrc for validation of clinical X-ray beams.

SpekPy

SpekPy is a free Python software toolkit and can be downloaded from here: https://bitbucket.org/spekpy/spekpy_release/wiki/Home.

It can be run from within a local Python installation or also run online as a Jupyter package from the website.

Common SpekPy commands:

  • #intiate SpekPy from the python command line

  • import spekpy as sp

  • #create spectrum with kV and target angle

  • s=sp.Spek(kv=100,th=25)

  • #add filters

  • s.filter(‘Be’,1.0).filter(‘Al’,4.5),filter(‘Air’,1000)

  • #check calculated HVL in aluminium

  • hvl=s.get_hvl1(‘Al’); print(hvl)

  • #export spectrum

  • s.export_spectrum(‘output.txt’)

The format of the spectrum that is output from SpekPy must converted into the required EGSnrc format. This is done as follows with the output.txt file.

  • Open the text file into a suitable text editor or MS Excel.

  • Remove the SpekPy header.

  • Convert each energy value from middle of bin to top of each bin.

  • Convert each energy value from units of keV to MeV.

  • Add EGSnrc spectrum header into row 1 which can be any free text.

  • The second row has three parameters being (1) the number of bins, (2) the lower energy of the first bin and (3) either 0 or 1 depending on normalization of your data.

  • For further information on the format of EGSnrc spectrum files refer to NRCC Report PIRS 702 (https://nrc-cnrc.github.io/EGSnrc/doc/pirs702-egsnrc-codes.pdf).

Also note that by default the spectrum files are limited to 300 entries. The energy bin width of spectra generated can be changed with the dk parameter in the Spek function.

EGSnrc

The EGSnrc installation instructions can be found here: https://github.com/nrc-cnrc/EGSnrc/wiki/Installation-overview.

New users to EGSnrc are recommended to spend time going through the tutorial program first in “Getting Started with EGSnrc”.

Copy and rename the dosrznrc_template.egsinp file to an appropriate name. The egsinp files are located in the EGSrnc\EGS_HOME\dosrznrc directory.

Open the egs_inprz gui which will be used to run the DOSRZnrc user code. The gui can be found in the EGSnrc\HEN_HOUSE\bin directory or sub-directory and load the egsinp file. Detailed information on these codes can be found in the EGSnrc documentation.

Adjust the parameters in the various tabs of egs_inprz gui as per the example given in Table 3. The various parameters have been set for optimal dose calculations in the kilovoltage X-ray beam energy range.

Table 3 Example parameters for the egs_inprz_nrc gui
Full size table

Save the egsinp file, compile (first time only) and execute. After completion, analyse voxel doses recorded in the egslst file or plotdata files in the dosrznrc directory. Further information: SpekPy: https://bitbucket.org/spekpy/spekpy_release/wiki/Home EGSnrc: https://github.com/nrc-cnrc/EGSnrchttps://www.reddit.com/r/EGSnrc/

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Healy, B.J., Hill, R.F. Use of calculations to validate beam quality and relative dose measurements for a kilovoltage X-ray therapy unit. Phys Eng Sci Med 45, 537–546 (2022). https://doi.org/10.1007/s13246-022-01120-8

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