Localization of electron virtual SSD in a Siemens-Primus linear accelerator: Comparison of measurements with Monte Carlo simulation

Document Type : Conference Proceedings


1 Mahdieh Radiotherapy and Oncology charity Centre, Hamadan. Iran Islamic Azad University, Science and Research Branch, Tehran, Iran

2 Department of Medical Physics, Royal Adelaide Hospital, Adelaide, SA 5000 AUSTRALIA. School of Physical Sciences, the University of Adelaide, SA 5005 AUSTRALIA. Department of Medical Physics, Reza Radiotherapy and Oncology Center, Mashhad, Iran.

3 Department of radiation oncology, University of medical science, Hamedan, Iran.


Introduction: Because of importance of impact of the Source to Surface Distance (SSD) in determining of monitor unit for electron-therapy, it is essential to know the Virtual Source Position (VSP) for electron beam for a linear therapeutic accelerator for each energy and field size.
, especially using the Khan method (photo distance squared method) And compare the results with Monte Carlo.
Materials and Methods: The VSP was measured for a Siemens- Primus linear accelerator for all available electron beams (5, 7, 8, 10 and 12 MeV) and for five applicator sizes (5×5, 10×10, 15×15, 20×20, 25×25 cm2) available at the department in Mahdieh Radiotherapy and Oncology Charity center in Hamadan. A theoretical method (known as Khan’s method) was applied to estimate VSP for all electron energies and for all potential applicators. A valid MCNPX Monte Carlo code was then used to evaluate the results achieved through the measurements.
Results:The results showed a significant difference between Monte Carlo those were found to be ~4% and 5.2% for F4 and F8 tally approaches, respectively.
Conclusion: MonteCarlo simulation code with correction factor can be used as an alternative approach to verify measurements acquired for VSD and other datasets applied for treatment Planning Systems.


  • Receive Date: 21 May 2018
  • Revise Date: 28 November 2018
  • Accept Date: 06 July 2018
  • First Publish Date: 01 December 2018