A comparison of surface doses for very small field size x-ray beams: Monte Carlo calculations and radiochromic film measurements

  • J. E. MoralesEmail author
  • R. Hill
  • S. B. Crowe
  • T. Kairn
  • J. V. Trapp
Scientific Paper


Stereotactic radiosurgery treatments involve the delivery of very high doses for a small number of fractions. To date, there is limited data in terms of the skin dose for the very small field sizes used in these treatments. In this work, we determine relative surface doses for small size circular collimators as used in stereotactic radiosurgery treatments. Monte Carlo calculations were performed using the BEAMnrc code with a model of the Novalis Trilogy linear accelerator and the BrainLab circular collimators. The surface doses were calculated at the ICRP skin dose depth of 70 μm all using the 6 MV SRS x-ray beam. The calculated surface doses varied between 15 and 12 % with decreasing values as the field size increased from 4 to 30 mm. In comparison, surface doses were measured using Gafchromic EBT3 film positioned at the surface of a Virtual Water phantom. The absolute agreement between calculated and measured surface doses was better than 2.0 % which is well within the uncertainties of the Monte Carlo calculations and the film measurements. Based on these results, we have shown that the Gafchromic EBT3 film is suitable for surface dose estimates in very small size fields as used in SRS.


Stereotactic radiosurgery SRS Surface dosimetry skin dose Monte Carlo calculations Radiochromic film EBT3 



Computational resources and services used in this work were provided by the High Performance Computing and Research Support Unit, Queensland University of Technology, Brisbane, Australia. Also, we’d like to acknowledge that Dr S. B. Crowe’s contribution to this work was supported by the Australian Research Council through Linkage Grant No. LP110100401.


  1. 1.
    Warrington J (2007) Stereotactic Techniques. In: Mayles P, Nahum AE, Rosenwald J (eds) Handbook of Radiotherapy Physics, CRC Press, Boca Raton, pp 987–1003Google Scholar
  2. 2.
    Devic S et al (2006) Accurate skin dose measurements using radiochromic film in clinical applications. Med Phys 33(4):1116–1124PubMedCrossRefGoogle Scholar
  3. 3.
    Hsu SH et al (2008) Assessment of skin dose for breast chest wall radiotherapy as a function of bolus material. Phys Med Biol 53(10):2593–2606PubMedCrossRefGoogle Scholar
  4. 4.
    Kry SF et al (2012) Skin dose during radiotherapy: a summary and general estimation technique. J Appl Clin Med Phys 13(3):20–34Google Scholar
  5. 5.
    ICRP The biological basis for dose limitation in the skin (1992). ICRPGoogle Scholar
  6. 6.
    Kim KA et al (2013) Development of a fibre-optic dosemeter to measure the skin dose and percentage depth dose in the build-up region of therapeutic photon beams. Radiat Prot Dosim 153(3):294–299CrossRefGoogle Scholar
  7. 7.
    Dogan N, Glasgow GP (2003) Surface and build-up region dosimetry for obliquely incident intensity modulated radiotherapy 6 MV x-rays. Med Phys 30(12):3091–3096PubMedCrossRefGoogle Scholar
  8. 8.
    Moylan R, Aland T, Kairn T (2013) Dosimetric accuracy of Gafchromic EBT2 and EBT3 film for in vivo dosimetry. Australasian Phys Eng Sci Med 36(3):331–337CrossRefGoogle Scholar
  9. 9.
    Chung H et al (2005) Evaluation of surface and build-up region dose for intensity-modulated radiation therapy in head and neck cancer. Med Phys 32:2682PubMedCrossRefGoogle Scholar
  10. 10.
    Court LE et al (2008) Experimental evaluation of the accuracy of skin dose calculation for a commercial treatment planning system. J Appl Clin Med Phys 9(1):29–35CrossRefGoogle Scholar
  11. 11.
    Deng J et al (2003) Commissioning 6 MV photon beams of a stereotactic radiosurgery system for Monte Carlo treatment planning. Med Phys 30(12):3124–3134PubMedCrossRefGoogle Scholar
  12. 12.
    Gerbi BJ, Khan FM (1990) Measurement of dose in the buildup region using fixed-separation plane-parallel ionization chambers. Med Phys 17(1):17–26PubMedCrossRefGoogle Scholar
  13. 13.
    Kim S et al (1998) Photon beam skin dose analyses for different clinical setups. Med Phys 25(6):860–866PubMedCrossRefGoogle Scholar
  14. 14.
    Kron T et al (1993) X-ray surface dose measurements using TLD extrapolation. Med Phys 20:703PubMedCrossRefGoogle Scholar
  15. 15.
    Kwan IS et al (2008) Skin dosimetry with new MOSFET detectors. Radiat Meas 43(2–6):929–932CrossRefGoogle Scholar
  16. 16.
    Nelson VK, Hill RF (2011) Backscatter factor measurements for kilovoltage X-ray beams using thermoluminescent dosimeters (TLDs). Radiat Meas 46(12):2097–2099CrossRefGoogle Scholar
  17. 17.
    Roberson PL, Moran JM, Kulasekere R (2008) Radiographic film dosimetry for IMRT fields in the near-surface buildup region. J Appl Clin Med Phys 9(4):87–97CrossRefGoogle Scholar
  18. 18.
    Xiang HF et al (2007) Build-up and surface dose measurements on phantoms using micro-MOSFET in 6 and 10 MV x-ray beams and comparisons with Monte Carlo calculations. Med Phys 34(4):1266–1273PubMedCrossRefGoogle Scholar
  19. 19.
    Sors A et al (2013) An optimized calibration method for surface measurements with MOSFETs in shaped-beam radiosurgery. Physica MedicaGoogle Scholar
  20. 20.
    Nakano M et al (2012) A study of surface dosimetry for breast cancer radiotherapy treatments using Gafchromic EBT2 film. J Appl Clin Med Phys 13(3):83–97Google Scholar
  21. 21.
    Rogers DWO (2006) Fifty years of Monte Carlo simulations for medical physics. Phys Med Biol 51(13)Google Scholar
  22. 22.
    Rogers DWO et al (1995) BEAM: a Monte Carlo code to simulate radiotherapy treatment units. Med Phys 22(5):503–524PubMedCrossRefGoogle Scholar
  23. 23.
    Verhaegen F, Seuntjens J (2003) Monte Carlo modelling of external radiotherapy photon beams. Phys Med Biol 48(21)Google Scholar
  24. 24.
    Abdel-Rahman W et al (2005) Validation of Monte Carlo calculated surface doses for megavoltage photon beams. Med Phys 32(1):286–298PubMedCrossRefGoogle Scholar
  25. 25.
    Kim JH, Hill R, Kuncic Z (2012) Practical considerations for reporting surface dose in external beam radiotherapy: a 6 MV X-ray beam study. Australasian Phys Eng Sci Med 35(3):271–282CrossRefGoogle Scholar
  26. 26.
    Kim JH, Hill R, Kuncic Z (2012) An evaluation of calculation parameters in the EGSnrc/BEAMnrc Monte Carlo codes and their effect on surface dose calculation. Phys Med Biol 57(14):N267–N278PubMedCrossRefGoogle Scholar
  27. 27.
    Apipunyasopon L, Srisatit S, Phaisangittisakul N (2013) An investigation of the depth dose in the build-up region, and surface dose for a 6 MV therapeutic photon beam: Monte Carlo simulation and measurements. J Radiat Res 54(2):374–382PubMedCrossRefPubMedCentralGoogle Scholar
  28. 28.
    Ding GX, Duggan DM, Coffey CW (2006) Commissioning stereotactic radiosurgery beams using both experimental and theoretical methods. Phys Med Biol 51(10):2549–2566PubMedCrossRefGoogle Scholar
  29. 29.
    Paskalev KA et al (2003) Physical aspects of dynamic stereotactic radiosurgery with very small photon beams (1.5 and 3 mm in diameter). Med Phys 30(2):111–118PubMedCrossRefGoogle Scholar
  30. 30.
    Chang Z et al (2008) Dosimetric characteristics of novalis Tx system with high definition multileaf collimator. Med Phys 35(10):4460–4463PubMedCrossRefGoogle Scholar
  31. 31.
    Dhabaan A et al (2010) Dosimetric performance of the new high-definition multileaf collimator for intracranial stereotactic radiosurgery. J Appl Clin Med Phys 11(3):197–211Google Scholar
  32. 32.
    Yin F–F et al (2002) Dosimetric characteristics of Novalis shaped beam surgery unit. Med Phys 29(8):1729–1738PubMedCrossRefGoogle Scholar
  33. 33.
    Kawrakow I (2000) Accurate condensed history Monte Carlo simulation of electron transport I EGSnrc, the new EGS4 version. Med Phys 27(3):485–498PubMedCrossRefGoogle Scholar
  34. 34.
    Rogers DWO, Walters BRB, Kawrakow I (2005) BEAMnrc users manual ionizing radiation standards. National Research Council of Canada, OttawaGoogle Scholar
  35. 35.
    Kawrakow I, Rogers DWO, Walters BRB (2004) Large efficiency improvements in BEAMnrc using directional bremsstrahlung splitting. Med Phys 31:2883–2898PubMedCrossRefGoogle Scholar
  36. 36.
    Kawrakow I, Walters BRB (2006) Efficient photon beam dose calculations using DOSXYZnrc with BEAMnrc. Med Phys 33(8):3046–3056PubMedCrossRefGoogle Scholar
  37. 37.
    Walters BRB, Kawrakow I (2007) Technical note: overprediction of dose with default PRESTA-I boundary crossing in DOSXYZnrc and BEAMnrc. Med Phys 34(2):647–650PubMedCrossRefGoogle Scholar
  38. 38.
    ICRP59 (1991) The biological basis for dose limitation in the skin. Ann 22(2)Google Scholar
  39. 39.
    Casanova BV et al (2013) Dosimetric characterization and use of GAFCHROMIC EBT3 film for IMRT dose verification. J Appl Clin Med phys/American Coll Med Phys 14(2):4111Google Scholar
  40. 40.
    Reinhardt S et al (2012) Comparison of Gafchromic EBT2 and EBT3 films for clinical photon and proton beams. Med Phys 39:5257PubMedCrossRefGoogle Scholar
  41. 41.
    Hill R, Kuncic Z, Baldock C (2010) The water equivalence of solid phantoms for low energy photon beams. Med Phys 37(8):4355–4363PubMedCrossRefGoogle Scholar
  42. 42.
    ISO Guide to the expression of uncertainties in measurement (1995). International Organisation for Standardization, Geneva Google Scholar
  43. 43.
    McEwen MR, Kawrakow I, Ross CK (2008) The effective point of measurement of ionization chambers and the build-up anomaly in MV X-ray beams. Med Phys 35(3):950–958PubMedCrossRefGoogle Scholar
  44. 44.
    Hill R et al (2009) An evaluation of ionization chambers for the relative dosimetry of kilovoltage X-ray beams. Med Phys 36(9):3971–3981PubMedCrossRefGoogle Scholar
  45. 45.
    Low DA et al (1998) A techinique for the quantitative evaluation of dose distributions. Med Phys 25(5):656–661PubMedCrossRefGoogle Scholar
  46. 46.
    Ding GX (2002) Energy spectra, angular spread, fluence profiles and dose distributions of 6 and 18 MV photon beams: results of Monte Carlo simulations for a Varian 2100EX accelerator. Phys Med Biol 47:1025–1046PubMedCrossRefGoogle Scholar
  47. 47.
    Hoppe BS et al (2008) Acute skin toxicity following stereotactic body radiation therapy for stage I non-small-cell lung cancer: Who is at risk?. Int J Rad Oncol Bio Phys 72:1283–1286Google Scholar
  48. 48.
    Kelly A et al (2011) Surface dosimetry for breast radiotherapy in the presence of immobilization cast material. Phys Med Biol 56(4):1001–1013PubMedCrossRefGoogle Scholar

Copyright information

© Australasian College of Physical Scientists and Engineers in Medicine 2014

Authors and Affiliations

  • J. E. Morales
    • 1
    • 2
    Email author
  • R. Hill
    • 2
  • S. B. Crowe
    • 1
  • T. Kairn
    • 1
    • 3
  • J. V. Trapp
    • 1
  1. 1.School of Chemistry, Physics and Mechanical EngineeringQueensland University of TechnologyBrisbaneAustralia
  2. 2.Department of Radiation OncologyChris O’Brien LifehouseSydneyAustralia
  3. 3.Genesis Cancer Care (Queensland)The Wesley Medical CentreBrisbaneAustralia

Personalised recommendations