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.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
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.
IAEA TRS 398,Absorbed Dose Determination in External Beam Radiotherapy Technical Report Series no. 398, International Atomic Energy Agency, Vienna, 2000.
AAPM TG 61,AAPM protocol for 40–300 kV x-ray beam dosimetry in radiotherapy and radiobiology, Med. Phys., 28:868–893, 2001.
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.
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.
Jones, D. E. A., Raine, H. C., (letter), Br. J. Radiol. 22:540–50, 1949.
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.
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.
Podgorsak, E. B., Gosselin, M., Evans, M. D. C.,Superficial and orthovoltage x-ray beam dosimetry, Med. Phys., 25:1206–1211, 1998.
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.
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.
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.
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.
White, D. R.,The formulation of substitute materials with predetermined characteristics of radiation absorption and scattering, PhD thesis, University of London, London, 1974.
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.
Boone, J. M., Chavez, A. E.,Comparison of x-ray cross sections for diagnostic and therapeutic medical physics, Med. Phys., 23:1997–2005, 1996.
BJR Supplement 25,Central axis depth dose data for use in Radiotherapy, British Institute of Radiology, London, 1996.
Khan, F. M.,The Physics of Radiation Therapy, 2nd ed., Williams and Wilkins, Baltimore, p.126, 1994.
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.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Healy, B.J., Gibbs, A., Murry, R.L. et al. Output factor measurements for a kilovoltage x-ray therapy unit. Australas. Phys. Eng. Sci. Med. 28, 115–121 (2005). https://doi.org/10.1007/BF03178702
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF03178702