Advertisement

Output factor measurements for a kilovoltage x-ray therapy unit

  • B. J. Healy
  • A. Gibbs
  • R. L. Murry
  • J. E. Prunster
  • K. N. Nitschke
Technical Report

Abstract

Output factors at the surface for treatment cones and lead cut-outs have been measured for a Pantak Therapax SXT 150 superficial therapy unit with x-ray beam qualities from 1 to 13 mm Al HVL. A variety of phantom materials and two ionisation chambers were tested for their suitability in output factor and percentage depth dose measurement. Solid water proved a useful water-equivalent phantom material with discrepancies between measurements in water and solid water less than 2.3% for percentage depth dose and less than 0.6% for output factors. Larger measurement discrepancies were found for Plastic Water and Perspex. A PTW Markus chamber was found to compare well with a NE 2532/3 low energy chamber in percentage depth dose measurement, but discrepancies arose between the chambers in output factor measurements, up to 5% for small field sizes. Measurements indicated that the Markus chamber had an energy dependent response in the kilovoltage range, which could account for the discrepancy in output factor measurement.

Key words

output factors kilovoltage x-rays ionisation chambers water substitutes 

References

  1. 1.
    IPEMB 1996,The IPEMB code of practice for the determination of absorbed dose for x-rays below 300 kV generating potential (0.035 m Al — 4 mm Cu HVL; 10 –300 kV generating potential), Phys. Med. Biol., 41:2605–2625, 1996.CrossRefGoogle Scholar
  2. 2.
    IAEA TRS 398,Absorbed Dose Determination in External Beam Radiotherapy Technical Report Series no. 398, International Atomic Energy Agency, Vienna, 2000.Google Scholar
  3. 3.
    AAPM TG 61,AAPM protocol for 40–300 kV x-ray beam dosimetry in radiotherapy and radiobiology, Med. Phys., 28:868–893, 2001.CrossRefGoogle Scholar
  4. 4.
    Allen Li, X., Ma, C-M., Salhani, D.,Relative dosimetry measurement for kilovoltage x-ray units, in Kilovoltage x-ray beam dosimetry for radiotherapy and radiobiology C—M Ma and J.P. Seuntjens (Eds.), Proceedings, Medical Physics Publishing, Madison, 1999.Google Scholar
  5. 5.
    Ipe, N. E., Rosser, K. E., Moretti, C. J., Manning, J. W., Palmer, M. J.,Air kerma calibration factors and chamber correction values for PTW soft x-ray, NACP and Roos ionisation chambers at very low x-ray energies, Phys. Med. Biol., 46:2107–2117, 2001.CrossRefPubMedGoogle Scholar
  6. 6.
    Jones, D. E. A., Raine, H. C., (letter), Br. J. Radiol. 22:540–50, 1949.CrossRefGoogle Scholar
  7. 7.
    Perrin, B. A., Whitehurst, P., Cooper, P., Hounsell, A. R.,The measurement of k ch factors for application with the IPEMB very low energy dosimetry protocol, Phys. Med. Biol., 46:1985–1995, 2001.CrossRefPubMedGoogle Scholar
  8. 8.
    Klevenhagen, S. C.,The build-up of backscatter in the energy range 1 mm Al to 8 mm Al HVT, Phys. Med. Biol., 27:1035–1043, 1982.CrossRefGoogle Scholar
  9. 9.
    Podgorsak, E. B., Gosselin, M., Evans, M. D. C.,Superficial and orthovoltage x-ray beam dosimetry, Med. Phys., 25:1206–1211, 1998.CrossRefPubMedGoogle Scholar
  10. 10.
    Meigooni, A. S., Li, Z., Mishra, V., Williamson, J. F.,A comparative study of dosimetric properties of Plastic Water and Solid Water in brachytherapy applications, Med. Phys., 21:1983–1987, 1994.CrossRefPubMedGoogle Scholar
  11. 11.
    Allen Li, X., Ma, C-M., Salhani, D.,Measurement of percentage depth dose and lateral beam profile for kilovoltage x-ray therapy beams, Phys. Med. Biol., 42:2561–68, 1997.CrossRefGoogle Scholar
  12. 12.
    Hill, R., Keall, P.J., Beckham, W.A., Perez, M.D.,Photon build up in orthovoltage x-ray beams, Australas. Phys. Eng. Sci. Med., 21:51–56, 1998.PubMedGoogle Scholar
  13. 13.
    Klevenhagen, S. C., D’Souza, D., Bonnefaux, I.,Complications in low energy x-ray dosimetry caused by electron contamination, Phys. Med. Biol., 36:1111–1116, 1991.CrossRefGoogle Scholar
  14. 14.
    White, D. R.,The formulation of substitute materials with predetermined characteristics of radiation absorption and scattering, PhD thesis, University of London, London, 1974.Google Scholar
  15. 15.
    Constantinou, C., Attix, F. H., Paliwal, B. R.,A solid water phantom material for radiotherapy x-ray and ?-ray beam calibrations, Med. Phys., 9:436–441, 1982.CrossRefPubMedGoogle Scholar
  16. 16.
    Boone, J. M., Chavez, A. E.,Comparison of x-ray cross sections for diagnostic and therapeutic medical physics, Med. Phys., 23:1997–2005, 1996.CrossRefPubMedGoogle Scholar
  17. 17.
    BJR Supplement 25,Central axis depth dose data for use in Radiotherapy, British Institute of Radiology, London, 1996.Google Scholar
  18. 18.
    Khan, F. M.,The Physics of Radiation Therapy, 2nd ed., Williams and Wilkins, Baltimore, p.126, 1994.Google Scholar
  19. 19.
    Tello, V. M., Tailor, R. C., and Hanson, W.F.,How water equivalent are water-equivalent solid materials for output calibration of photon and electron beams? Med. Phys., 22:1177–89, 1995.CrossRefPubMedGoogle Scholar

Copyright information

© Australasian College of Physical Scientists and Engineers in Medicine 2005

Authors and Affiliations

  • B. J. Healy
    • 1
  • A. Gibbs
    • 1
  • R. L. Murry
    • 1
  • J. E. Prunster
    • 1
  • K. N. Nitschke
    • 1
  1. 1.Southern Zone Radiation Oncology Service-Mater CentrePrincess Alexandra HospitalSouth BrisbaneAustralia

Personalised recommendations