Analytical Consideration of Surface Dose and Kerma for Megavoltage Photon Beams in Clinical Radiation Therapy

  • Birgani, Mohammad Javad Tahmasebi ;
  • Behrooz, Mohammad Ali ;
  • Razmjoo, Sasan ;
  • Zabihzadeh, Mansour ;
  • Fatahiasl, Jafar ;
  • Maskni, Reza ;
  • Abdalvand, Neda ;
  • Asgarian, Zeynab ;
  • Shamsi, Azin
  • Published : 2016.02.05


Background: In radiation therapy, estimation of surface doses is clinically important. This study aimed to obtain an analytical relationship to determine the skin surface dose, kerma and the depth of maximum dose, with energies of 6 and 18 megavoltage (MV). Materials and Methods: To obtain the dose on the surface of skin, using the relationship between dose and kerma and solving differential equations governing the two quantities, a general relationship of dose changes relative to the depth was obtained. By dosimetry all the standard square fields of $5cm{\times}5cm$ to $40cm{\times}40cm$, an equation similar to response to differential equations of the dose and kerma were fitted on the measurements for any field size and energy. Applying two conditions: a) equality of the area under dose distribution and kerma changes in versus depth in 6 and 18 MV, b) equality of the kerma and dose at $x=d_{max}$ and using these results, coefficients of the obtained analytical relationship were determined. By putting the depth of zero in the relation, amount of PDD and kerma on the surface of the skin, could be obtained. Results: Using the MATLAB software, an exponential binomial function with R-Square >0.9953 was determined for any field size and depth in two energy modes 6 and 18MV, the surface PDD and kerma was obtained and both of them increase due to the increase of the field, but they reduce due to increased energy and from the obtained relation, depth of maximum dose can be determined. Conclusions: Using this analytical formula, one can find the skin surface dose, kerma and thickness of the buildup region.


Dosimetry;skin surface dose;kerma;percentage depth dose;buildup region


  1. Apipunyasopon L, Phaisangittisakul N, Srisatit S (2013). Equivalent square formula for determining the surface dose of rectangular field from 6 MV therapeutic photon beam. J Appl Clin Med Physics, 14.
  2. Attix FH 2008. Introduction to radiological physics and radiation dosimetry, John Wiley & Sons.
  3. Bilge H, Cakir A, Okutan M, et al (2009). Surface dose measurements with GafChromic EBT film for 6 and 18MV photon beams. Physica Med, 25, 101-4.
  4. Butson M, Mathur J, Metcalfe P (1997). Skin dose from radiotherapy X-ray beams: The influence of energy. Australasian Radiol, 41, 148-50.
  5. Butson MJ, Cheung T, Peter K, et al (2004). Surface dose extrapolation measurements with radiographic film. Physics Med Biol, 49, 197.
  6. Charles M, Khan Z (1978). Implementation of the ICRP recommendation on skin dose measurement using thermoluminescent dosemeters. Physics Med Biol, 23, 972.
  7. Cora S, Francescon P (1995). Accurate build-up and surface dose measurements of megavolt photon beams from variety of accelerators. Phys Med, 11, 17-22.
  8. Devic S, Seuntjens J, Abdel-Rahman W, et al (2006). Accurate skin dose measurements using radiochromic film in clinical applications. Medical Physics, 33, 1116-24.
  9. Ishmael Parsai E, Shvydka D, Pearson D, et al (2008). Surface and build-up region dose analysis for clinical radiotherapy photon beams. Applied Radiat Isotopes, 66, 1438-42.
  10. Jornet N, Ribas M, Eudaldo T (2000). In vivo dosimetry: intercomparison between p-type based and n-type based diodes for the 16-25 MV energy range. Med Physics, 27, 1287-93.
  11. Klein EE, Esthappan J, Li Z (2003). Surface and buildup dose characteristics for 6, 10, and 18 MV photons from an Elekta Precise linear accelerator. J Applied Clin Med Physics, 4, 1-7.
  12. Lin J-P, Chu T-C, Lin S-Y, et al (2001). Skin dose measurement by using ultra-thin TLDs. Applied Radiat Isotopes, 55, 383-91.
  13. Loevinger R (1981). A formalism for calculation of absorbed dose to a medium from photon and electron beams. Medical physics,8, 1-12.
  14. Nilsson B, Montelius A (1986). Fluence perturbation in photon beams under nonequilibrium conditions. Med Physics, 13, 191-5.
  15. Ravikumar M, Ravichandran R (2000). Dose measurements in the build-up region for the photon beams from Clinac-1800 dual energy medical linear accelerator. Strahlentherapie und Onkologie, 176, 223-8.
  16. Scalchi P, Francescon P, Rajaguru P (2005). Characterization of a new MOSFET detector configuration for in vivo skin dosimetry. Medical physics, 32, 1571-8.
  17. Tannous N, Gagnon W, Almond P (1981). Buildup region and skin-dose measurements for the Therac 6 Linear Accelerator for radiation therapy. Medical Physics, 8, 378-81.
  18. Xiang HF, Song JS, Chin DW, et al (2007). Build-up and surface dose measurements on phantoms using micro-MOSFET in 6 and 10MV x-ray beams and comparisons with Monte Carlo calculations. Medical Physics,34, 1266-73.


Supported by : Ahvaz Jundishapur university of medical sciences